GML Publications for 2022

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A
Asher, Elizabeth, Troy Thornberry, David W. Fahey, Allison McComiskey, Kenneth Carslaw, Sophie Grunau, Kai‐Lan Chang, Hagen Telg, Ping Chen and Ru‐Shan Gao, (2022), A Novel Network‐Based Approach to Determining Measurement Representation Error for Model Evaluation of Aerosol Microphysical Properties, Journal of Geophysical Research: Atmospheres, 127, 3, 10.1029/2021JD035485

Abstract

Atmospheric aerosol size and abundance influence radiative effects and climate change. To date, efforts to constrain global climate models' radiative forcing with in situ aerosol observations have been hamstrung by uncertainty. One source of error, the regional “representation error,” arises when accurate but sparse single-point measurements of atmospheric aerosol distributions are compared with a model value, assuming that the single-point measurement is representative of the model domain. The Portable Optical Particle Spectrometer network in the Southern Great Plains (POPSnet-SGP) campaign has demonstrated that a network of nearly autonomous aerosol instruments operating at ambient temperature and relative humidity (with low measurement error) may be used to quantify measurement representation error and investigate the factors introducing heterogeneity in aerosol distributions across a rural, continental background region. Measurements were made using Portable Optical Particle Spectrometer (POPS) instruments at several sites for five months across the Department of Energy's Aerosol Radiation Measurement Southern Great Plains (ARM-SGP) User Facility in the central USA. Measurement representation error decreased with longer averaging periods (20%–40% between 1 s and 1 day), varied between sites by 10%–20% for aerosol concentration 140–2,500 nm in diameter (N_140), and was higher for aerosols >400 nm in diameter (N_400). Our measurements also show the influence of local meteorology on aerosol surface area (A_140) and size distributions: A_140 is positively correlated with wind speed and relative humidity, negatively correlated with precipitation, and lower given westerly winds. We conclude that the POPSnet approach provides considerably more insight into the spatial variability in the aerosol population that can be used to constrain climate models than would be available from similar networks of PM 2.5 monitors.

Augustine, John A. and Antonietta Capotondi, (2022), Forcing for Multidecadal Surface Solar Radiation Trends Over Northern Hemisphere Continents, Journal of Geophysical Research: Atmospheres, 127, 16, 10.1029/2021JD036342

Abstract

The long-term variation of North Pacific and North Atlantic sea surface temperatures (SSTs) is shown to be associated with multidecadal trends of surface solar radiation in North America, Europe, and Asia. Long-term, large-scale warm SST anomalies lead to a mid-level planetary wave anomaly pattern of geopotential height ridges over the warm water and dynamically-induced lower heights on either side, sometimes extending over adjacent continents. Geopotential height troughs over the continents encourage more cloud cover and dimming of surface solar radiation. Conversely, cool SST anomalies correspond to a pattern of lower mid-level geopotential heights over the cool water and compensating high pressure on either side that encourages decreasing cloud cover and brightening over the continents, if the wave positioning is favorable. Additionally, these effects are observed to be latitude dependent, showing stronger SST-geopotential height associations in the northern half of the Northern Hemisphere. The change from continental dimming to brightening and the reversal of North Pacific SST trends are nearly simultaneous. A similar SST-geopotential height association is seen in the North Atlantic and leads to brightening and dimming in Europe and North America, but there is a ∼12-year lag between the transition of dimming to brightening and SST reversals there, which is yet unexplained. The next step is to support these connections and their latitudinal dependence with carefully designed numerical experiments that consider variable greenhouse gas and aerosol concentrations.

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Bahramvash Shams, Shima, Von P. Walden, James W. Hannigan, William J. Randel, Irina V. Petropavlovskikh, Amy H. Butler and Alvaro de la Cámara, (2022), Analyzing ozone variations and uncertainties at high latitudes during sudden stratospheric warming events using MERRA-2, Atmospheric Chemistry and Physics, 22, 8, 5435-5458, 10.5194/acp-22-5435-2022

Abstract

Abstract. Stratospheric circulation is a critical part of the Arctic ozone cycle. Sudden stratospheric warming events (SSWs) manifest the strongest alteration of stratospheric dynamics. During SSWs, changes in planetary wave propagation vigorously influence zonal mean zonal wind, temperature, and tracer concentrations in the stratosphere over the high latitudes. In this study, we examine six persistent major SSWs from 2004 to 2020 using the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2). Using the unique density of observations around the Greenland sector at high latitudes, we perform comprehensive comparisons of high-latitude observations with the MERRA-2 ozone dataset during the six major SSWs. Our results show that MERRA-2 captures the high variability of mid-stratospheric ozone fluctuations during SSWs over high latitudes. However, larger uncertainties are observed in the lower stratosphere and troposphere. The zonally averaged stratospheric ozone shows a dramatic increase of 9 %–29 % in total column ozone (TCO) near the time of each SSW, which lasts up to 2 months. This study shows that the average shape of the Arctic polar vortex before SSWs influences the geographical extent, timing, and magnitude of ozone changes. The SSWs exhibit a more significant impact on ozone over high northern latitudes when the average polar vortex is mostly elongated as seen in 2009 and 2018 compared to the events in which the polar vortex is displaced towards Europe. Strong correlation (R2=90  %) is observed between the magnitude of change in average equivalent potential vorticity before and after SSWs and the associated averaged total column ozone changes over high latitudes. This paper investigates the different terms of the ozone continuity equation using MERRA-2 circulation, which emphasizes the key role of vertical advection in mid-stratospheric ozone during the SSWs and the magnified vertical advection in elongated vortex shape as seen in 2009 and 2018.

Bernays, Noah, Daniel A. Jaffe, Irina Petropavlovskikh and Peter Effertz, (2022), Comment on “Comparison of ozone measurement methods in biomass burning smoke: an evaluation under field and laboratory conditions” by Long et al. (2021), Atmospheric Measurement Techniques, 15, 10, 3189-3192, 10.5194/amt-15-3189-2022

Abstract

Abstract. Long et al. (2021) conducted a detailed study of possible interferences in measurements of surface O3 by UV spectroscopy, which measures the UV transmission in ambient and O3-scrubbed air. While we appreciate the careful work done in this analysis, there were several omissions, and in one case, the type of scrubber used was misidentified as manganese dioxide (MnO2) when in fact it was manganese chloride (MnCl2). This misidentification led to the erroneous conclusion that all UV-based O3 instruments employing solid-phase catalytic scrubbers exhibit significant positive artifacts, whereas previous research found this not to be the case when employing MnO2 scrubber types. While the Long et al. (2021) study, and our results, confirm the substantial bias in instruments employing an MnCl2 scrubber, a replication of the earlier work with an MnO2 scrubber type and no humidity correction is needed.

Bernhard, Germar H., Richard L. McKenzie, Kathleen Lantz and Scott Stierle, (2022), Updated analysis of data from Palmer Station, Antarctica (64° S), and San Diego, California (32° N), confirms large effect of the Antarctic ozone hole on UV radiation, Photochemical & Photobiological Sciences, 10.1007/s43630-022-00178-3

Abstract

The status of the stratospheric ozone layer is assessed by a panel of experts every 4 years. Reports prepared by this panel include a section with common questions and answers (Q&A) about ozone depletion and related matters. Since 2002, this Q&A supplement has featured a plot comparing historical and current ultraviolet (UV) Index data from Palmer Station, Antarctica (64° S), with measurements at San Diego, California (32° N), and Barrow, Alaska (79° N). The assumptions in generating these plots are discussed and an updated version is presented. The revised plot uses additional data up to the year 2020 and the methods used to create it are better defined and substantiated compared to those used for the legacy plot. Differences between the old and new UV Index values are small (typically < 5%). Both versions illustrate that the ozone hole has led to a large increase in the UV Index at Palmer Station. Between mid-September and mid-November, the maximum UV Index at this site has more than doubled compared to the pre-ozone-hole era (i.e., prior to 1980). When Palmer Station was below the ozone hole in December 1998, an “extreme” UV Index of 14 was observed, exceeding the highest UV Index of 12 ever measured at San Diego despite the city’s subtropical latitude. Increases in the UV Index at Barrow and San Diego remain below 40% and 3%, respectively.

C
Chang, Kai‐Lan, Owen R. Cooper, Audrey Gaudel, Marc Allaart, Gerard Ancellet, Hannah Clark, Sophie Godin‐Beekmann, Thierry Leblanc, Roeland Van Malderen, Philippe Nédélec, Irina Petropavlovskikh, Wolfgang Steinbrecht, René Stübi, David W. Tarasick and Carlos Torres, (2022), Impact of the COVID‐19 Economic Downturn on Tropospheric Ozone Trends: An Uncertainty Weighted Data Synthesis for Quantifying Regional Anomalies Above Western North America and Europe, AGU Advances, 3, 2, 10.1029/2021AV000542

Abstract

This study quantifies the association between the COVID-19 economic downturn and 2020 tropospheric ozone anomalies above Europe and western North America, and their impact on long-term trends. Anomaly detection for an atmospheric time series is usually carried out by identifying potentially aberrant data points relative to climatological values. However, detecting ozone anomalies from sparsely sampled ozonesonde profiles (once per week at most sites) is challenging due to ozone's high temporal variability. We first demonstrate the challenges for summarizing regional trends based on independent time series from multiple nearby ozone profiling stations. We then propose a novel regional-scale anomaly detection framework based on generalized additive mixed models, which accounts for the sampling frequency and inherent data uncertainty associated with each vertical profile data set, measured by ozonesondes, lidar or commercial aircraft. This method produces a long-term monthly time series with high vertical resolution that reports ozone anomalies from the surface to the middle-stratosphere under a unified framework, which can be used to quantify the regional-scale ozone anomalies during the COVID-19 economic downturn. By incorporating extensive commercial aircraft data and frequently sampled ozonesonde profiles above Europe, we show that the complex interannual variability of ozone can be adequately captured by our modeling approach. The results show that free tropospheric ozone negative anomalies in 2020 are the most profound since the benchmark year of 1994 for both Europe and western North America, and positive trends over 1994–2019 are diminished in both regions by the 2020 anomalies.

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Godin-Beekmann, Sophie, Niramson Azouz, Viktoria F. Sofieva, Daan Hubert, Irina Petropavlovskikh, Peter Effertz, Gérard Ancellet, Doug A. Degenstein, Daniel Zawada, Lucien Froidevaux, Stacey Frith, Jeannette Wild, Sean Davis, Wolfgang Steinbrecht, Thierry Leblanc, Richard Querel, Kleareti Tourpali, Robert Damadeo, Eliane Maillard Barras, René Stübi, Corinne Vigouroux, Carlo Arosio, Gerald Nedoluha, Ian Boyd, Roeland Van Malderen, Emmanuel Mahieu, Dan Smale and Ralf Sussmann, (2022), Updated trends of the stratospheric ozone vertical distribution in the 60° S–60° N latitude range based on the LOTUS regression model, Atmospheric Chemistry and Physics, 22, 17, 11657-11673, 10.5194/acp-22-11657-2022

Abstract

Abstract. This study presents an updated evaluation of stratospheric ozone profile trends in the 60∘ S–60∘ N latitude range over the 2000–2020 period using an updated version of the Long-term Ozone Trends and Uncertainties in the Stratosphere (LOTUS) regression model that was used to evaluate such trends up to 2016 for the last WMO Ozone Assessment (2018). In addition to the derivation of detailed trends as a function of latitude and vertical coordinates, the regressions are performed with the datasets averaged over broad latitude bands, i.e. 60–35∘ S, 20∘ S–20∘ N and 35–60∘ N. The same methodology as in the last assessment is applied to combine trends in these broad latitude bands in order to compare the results with the previous studies. Longitudinally resolved merged satellite records are also considered in order to provide a better comparison with trends retrieved from ground-based records, e.g. lidar, ozonesondes, Umkehr, microwave and Fourier transform infrared (FTIR) spectrometers at selected stations where long-term time series are available. The study includes a comparison with trends derived from the REF-C2 simulations of the Chemistry Climate Model Initiative (CCMI-1). This work confirms past results showing an ozone increase in the upper stratosphere, which is now significant in the three broad latitude bands. The increase is largest in the Northern and Southern Hemisphere midlatitudes, with ∼2.2 ± 0.7 % per decade at ∼2.1 hPa and ∼2.1 ± 0.6 % per decade at ∼3.2 hPa respectively compared to ∼1.6 ± 0.6 % per decade at ∼2.6 hPa in the tropics. New trend signals have emerged from the records, such as a significant decrease in ozone in the tropics around 35 hPa and a non-significant increase in ozone in the southern midlatitudes at about 20 hPa. Non-significant negative ozone trends are derived in the lowermost stratosphere, with the most pronounced trends in the tropics. While a very good agreement is obtained between trends from merged satellite records and the CCMI-1 REF-C2 simulation in the upper stratosphere, observed negative trends in the lower stratosphere are not reproduced by models at southern and, in particular, at northern midlatitudes, where models report an ozone increase. However, the lower-stratospheric trend uncertainties are quite large, for both measured and modelled trends. Finally, 2000–2020 stratospheric ozone trends derived from the ground-based and longitudinally resolved satellite records are in reasonable agreement over the European Alpine and tropical regions, while at the Lauder station in the Southern Hemisphere midlatitudes they show some differences.

H
Hu, Lei, Stephen A. Montzka, Fred Moore, Eric Hintsa, Geoff Dutton, M. Carolina Siso, Kirk Thoning, Robert W. Portmann, Kathryn McKain, Colm Sweeney, Isaac Vimont, David Nance, Bradley Hall and Steven Wofsy, (2022), Continental-scale contributions to the global CFC-11 emission increase between 2012 and 2017, Atmospheric Chemistry and Physics, 22, 4, 2891-2907, 10.5194/acp-22-2891-2022

Abstract

Abstract. The detection of increasing global CFC-11 emissions after 2012 alerted society to a possible violation of the Montreal Protocol on Substances that Deplete the Ozone Layer (MP). This alert resulted in parties to the MP taking urgent actions. As a result, atmospheric measurements made in 2019 suggest a sharp decline in global CFC-11 emissions. Despite the success in the detection and mitigation of part of this problem, regions fully responsible for the recent global emission changes in CFC-11 have not yet been identified. Roughly two thirds (60 ± 40 %) of the emission increase between 2008–2012 and 2014–2017 and two thirds (60 ± 30 %) of the decline between 2014–2017 and 2019 were explained by regional emission changes in eastern mainland China. Here, we used atmospheric CFC-11 measurements made from two global aircraft surveys – the HIAPER (High-performance Instrumented Airborne Platform for Environmental Research) Pole-to-Pole Observations (HIPPO) in November 2009–September 2011 and the Atmospheric Tomography Mission (ATom) in August 2016–May 2018, in combination with the global CFC-11 measurements made by the US National Oceanic and Atmospheric Administration during these two periods – to derive global and regional emission changes in CFC-11. Our results suggest Asia accounted for the largest fractions of global CFC-11 emissions in both periods: 43 (37–52) % during November 2009–September 2011 and 57 (49–62) % during August 2016–May 2018. Asia was also primarily responsible for the emission increase between these two periods, accounting for 86 (59–115) % of the global CFC-11 emission rise between the two periods. Besides eastern mainland China, temperate western Asia and tropical Asia also contributed significantly to global CFC-11 emissions during both periods and likely to the global CFC-11 emission increase. The atmospheric observations further provide strong constraints on CFC-11 emissions from North America and Europe, suggesting that each of them accounted for 10 %–15 % of global CFC-11 emissions during the HIPPO period and smaller fractions in the ATom period. For South America, Africa, and Australia, the derived regional emissions had larger dependence on the prior assumptions of emissions and emission changes due to a lower sensitivity of the observations considered here to emissions from these regions. However, significant increases in CFC-11 emissions from southern hemispheric lands were not likely due to the observed increase of north-to-south interhemispheric gradients in atmospheric CFC-11 mole fractions from 2012–2017.

K
Konopka, Paul, Mengchu Tao, Felix Ploeger, Dale F. Hurst, Michelle L. Santee, Jonathon S. Wright and Martin Riese, (2022), Stratospheric Moistening After 2000, Geophysical Research Letters, 49, 8, 10.1029/2021GL097609

Abstract

The significant climate feedback of stratospheric water vapor (SWV) necessitates quantitative estimates of SWV budget changes. Model simulations driven by the newest European Centre for Medium-Range Weather Forecast reanalysis ERA5, satellite observations from the Stratospheric Water and OzOne Satellite Homogenized data set, Microwave Limb Sounder, and in situ frost point hygrometer observations from Boulder all show substantial and persistent stratospheric moistening after a sharp drop in water vapor at the turn of the millennium. This moistening occurred mainly during 2000–2006 and SWV abundances then remained high over the last decade. We find strong positive trends in the Northern Hemisphere and weak negative trends over the South Pole, mainly during austral winter. Moistening of the tropical stratosphere after 2000 occurred during late boreal winter/spring, reached values of ∼0.2 ppm/decade, was well correlated with a warming of the cold point tropopause by ∼0.4 K/decade and can only be partially attributed to El Nino-Southern Oscillation and volcanic eruptions.

Kuai, Le, Nicholas C. Parazoo, Mingjie Shi, Charles E. Miller, Ian Baker, Anthony A. Bloom, Kevin Bowman, Meemong Lee, Zhao‐Cheng Zeng, Roisin Commane, Stephen A. Montzka, Joe Berry, Colm Sweeney, John B. Miller and Yuk L. Yung, (2022), Quantifying Northern High Latitude Gross Primary Productivity (GPP) Using Carbonyl Sulfide (OCS), Global Biogeochemical Cycles, 36, 9, 10.1029/2021GB007216

Abstract

The northern high latitude (NHL, 40°N to 90°N) is where the second peak region of gross primary productivity (GPP) other than the tropics. The summer NHL GPP is about 80% of the tropical peak, but both regions are still highly uncertain (Norton et al. 2019, https://doi.org/10.5194/bg-16-3069-2019). Carbonyl sulfide (OCS) provides an important proxy for photosynthetic carbon uptake. Here we optimize the OCS plant uptake fluxes across the NHL by fitting atmospheric concentration simulation with the GEOS-CHEM global transport model to the aircraft profiles acquired over Alaska during NASA's Carbon in Arctic Reservoirs Vulnerability Experiment (2012–2015). We use the empirical biome-specific linear relationship between OCS plant uptake flux and GPP to derive the six plant uptake OCS fluxes from different GPP data. Such GPP-based fluxes are used to drive the concentration simulations. We evaluate the simulations against the independent observations at two ground sites of Alaska. The optimized OCS fluxes suggest the NHL plant uptake OCS flux of −247 Gg S year−1, about 25% stronger than the ensemble mean of the six GPP-based OCS fluxes. GPP-based OCS fluxes systematically underestimate the peak growing season across the NHL, while a subset of models predict early start of season in Alaska, consistent with previous studies of net ecosystem exchange. The OCS optimized GPP of 34 PgC yr−1 for NHL is also about 25% more than the ensembles mean from six GPP data. Further work is needed to fully understand the environmental and biotic drivers and quantify their rate of photosynthetic carbon uptake in Arctic ecosystems.

Kumar, Joshin, Theo Paik, Nishit J. Shetty, Patrick Sheridan, Allison C. Aiken, Manvendra K. Dubey and Rajan K. Chakrabarty, (2022), Correcting for filter-based aerosol light absorption biases at the Atmospheric Radiation Measurement program's Southern Great Plains site using photoacoustic measurements and machine learning, Atmospheric Measurement Techniques, 15, 15, 4569-4583, 10.5194/amt-15-4569-2022

Abstract

Abstract. Measurement of light absorption of solar radiation by aerosols is vital for assessing direct aerosol radiative forcing, which affects local and global climate. Low-cost and easy-to-operate filter-based instruments, such as the Particle Soot Absorption Photometer (PSAP), that collect aerosols on a filter and measure light attenuation through the filter are widely used to infer aerosol light absorption. However, filter-based absorption measurements are subject to artifacts that are difficult to quantify. These artifacts are associated with the presence of the filter medium and the complex interactions between the filter fibers and accumulated aerosols. Various correction algorithms have been introduced to correct for the filter-based absorption coefficient measurements toward predicting the particle-phase absorption coefficient (Babs). However, the inability of these algorithms to incorporate into their formulations the complex matrix of influencing parameters such as particle asymmetry parameter, particle size, and particle penetration depth results in prediction of particle-phase absorption coefficients with relatively low accuracy. The analytical forms of corrections also suffer from a lack of universal applicability: different corrections are required for rural and urban sites across the world. In this study, we analyzed and compared 3 months of high-time-resolution ambient aerosol absorption data collected synchronously using a three-wavelength photoacoustic absorption spectrometer (PASS) and PSAP. Both instruments were operated on the same sampling inlet at the Department of Energy's Atmospheric Radiation Measurement program's Southern Great Plains (SGP) user facility in Oklahoma. We implemented the two most commonly used analytical correction algorithms, namely, Virkkula (2010) and the average of Virkkula (2010) and Ogren (2010)–Bond et al. (1999) as well as a random forest regression (RFR) machine learning algorithm to predict Babs values from the PSAP's filter-based measurements. The predicted Babs was compared against the reference Babs measured by the PASS. The RFR algorithm performed the best by yielding the lowest root mean square error of prediction. The algorithm was trained using input datasets from the PSAP (transmission and uncorrected absorption coefficient), a co-located nephelometer (scattering coefficients), and the Aerosol Chemical Speciation Monitor (mass concentration of non-refractory aerosol particles). A revised form of the Virkkula (2010) algorithm suitable for the SGP site has been proposed; however, its performance yields approximately 2-fold errors when compared to the RFR algorithm. To generalize the accuracy and applicability of our proposed RFR algorithm, we trained and tested it on a dataset of laboratory measurements of combustion aerosols. Input variables to the algorithm included the aerosol number size distribution from the Scanning Mobility Particle Sizer, absorption coefficients from the filter-based Tricolor Absorption Photometer, and scattering coefficients from a multiwavelength nephelometer. The RFR algorithm predicted Babs values within 5 % of the reference Babs measured by the multiwavelength PASS during the laboratory experiments. Thus, we show that machine learning approaches offer a promising path to correct for biases in long-term filter-based absorption datasets and accurately quantify their variability and trends needed for robust radiative forcing determination.

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Langford, Andrew O., Christoph J. Senff, Raul J. Alvarez II, Ken C. Aikin, Sunil Baidar, Timothy A. Bonin, W. Alan Brewer, Jerome Brioude, Steven S. Brown, Joel D. Burley, Dani J. Caputi, Stephen A. Conley, Patrick D. Cullis, Zachary C. J. Decker, Stéphanie Evan, Guillaume Kirgis, Meiyun Lin, Mariusz Pagowski, Jeff Peischl, Irina Petropavlovskikh, R. Bradley Pierce, Thomas B. Ryerson, Scott P. Sandberg, Chance W. Sterling, Ann M. Weickmann and Li Zhang, (2022), The Fires, Asian, and Stratospheric Transport–Las Vegas Ozone Study (FAST-LVOS), Atmospheric Chemistry and Physics, 22, 3, 1707-1737, 10.5194/acp-22-1707-2022

Abstract

Abstract. The Fires, Asian, and Stratospheric Transport–Las Vegas Ozone Study (FAST-LVOS) was conducted in May and June of 2017 to study the transport of ozone (O3) to Clark County, Nevada, a marginal non-attainment area in the southwestern United States (SWUS). This 6-week (20 May–30 June 2017) field campaign used lidar, ozonesonde, aircraft, and in situ measurements in conjunction with a variety of models to characterize the distribution of O3 and related species above southern Nevada and neighboring California and to probe the influence of stratospheric intrusions and wildfires as well as local, regional, and Asian pollution on surface O3 concentrations in the Las Vegas Valley (≈ 900 m above sea level, a.s.l.). In this paper, we describe the FAST-LVOS campaign and present case studies illustrating the influence of different transport processes on background O3 in Clark County and southern Nevada. The companion paper by Zhang et al. (2020) describes the use of the AM4 and GEOS-Chem global models to simulate the measurements and estimate the impacts of transported O3 on surface air quality across the greater southwestern US and Intermountain West. The FAST-LVOS measurements found elevated O3 layers above Las Vegas on more than 75 % (35 of 45) of the sample days and show that entrainment of these layers contributed to mean 8 h average regional background O3 concentrations of 50–55 parts per billion by volume (ppbv), or about 85–95 µg m−3. These high background concentrations constitute 70 %–80 % of the current US National Ambient Air Quality Standard (NAAQS) of 70 ppbv (≈ 120 µg m−3 at 900 m a.s.l.) for the daily maximum 8 h average (MDA8) and will make attainment of the more stringent standards of 60 or 65 ppbv currently being considered extremely difficult in the interior SWUS.

Liang, Qing, Cynthia Nevison, Ed Dlugokencky, Bradley D. Hall and Geoff Dutton, (2022), 3‐D Atmospheric Modeling of the Global Budget of NO and Its Isotopologues for 1980–2019: The Impact of Anthropogenic Emissions, Global Biogeochemical Cycles, 36, 7, 10.1029/2021GB007202

Abstract

Nitrous oxide (N2O) is the third most important anthropogenic greenhouse gas and a major ozone-depleting substance. Its main sources include anthropogenic activities (mostly agriculture) and natural emissions from ocean and soils. However, emission estimates for individual sources are highly variable due to uncertainties in N2O lifetime estimates and partitioning among sources. We derive annual global N2O emissions for 1990–2019 using NOAA Global Monitoring Laboratory (GML) surface N2O observations and the N2O lifetime calculated in the NASA GEOS-5 chemistry climate model. The inferred global mean N2O emissions has gradually increased from ∼15.8 TgN/yr in the early 1990s to ∼17.8 TgN/yr in the 2010s. This implies that anthropogenic N2O emissions have grown rapidly from ∼6.7 TgN/yr in the 1990s to about ∼8.7 TgN/yr in the 2010s, a ∼30% increase. With specially designed N2O isotopic tracers in 3-D GEOSCCM, we estimate that, on global average, stratospheric enrichment contributes about +7.7‰/yr, +7.6‰/yr, +8.0‰/yr to tropospheric δ15Nα, δ15Nβ, and δ18O budget, respectively. To balance the global mean isotopic signature for pre-industrial terrestrial sources of δ15Nα ∼ 6.7‰, δ15Nβ ∼ −12.6‰, δ18O ∼ 35.4‰, our 3-dimensional isotopic budget simulation using the GEOSCCM suggests global mean anthropogenic isotopic signatures in the recent decades are δ15Nα ∼ −18‰, δ15Nβ ∼ −20‰, δ18O ∼ 19‰. These anthropogenic isotopic estimates are significantly lighter than results from one-box atmospheric model-based estimates with the largest difference seen for δ15Nβ. More surface isotopic measurements are needed to better quantify the N2O isotopic signatures.

Lu, Xiao, Daniel J. Jacob, Haolin Wang, Joannes D. Maasakkers, Yuzhong Zhang, Tia R. Scarpelli, Lu Shen, Zhen Qu, Melissa P. Sulprizio, Hannah Nesser, A. Anthony Bloom, Shuang Ma, John R. Worden, Shaojia Fan, Robert J. Parker, Hartmut Boesch, Ritesh Gautam, Deborah Gordon, Michael D. Moran, Frances Reuland, Claudia A. Octaviano Villasana and Arlyn Andrews, (2022), Methane emissions in the United States, Canada, and Mexico: evaluation of national methane emission inventories and 2010–2017 sectoral trends by inverse analysis of in situ (GLOBALVIEWplus CH4 ObsPack) and satellite (GOSAT) atmospheric observations, Atmospheric Chemistry and Physics, 22, 1, 395-418, 10.5194/acp-22-395-2022

Abstract

Abstract. We quantify methane emissions and their 2010–2017 trends by sector in the contiguous United States (CONUS), Canada, and Mexico by inverse analysis of in situ (GLOBALVIEWplus CH4 ObsPack) and satellite (GOSAT) atmospheric methane observations. The inversion uses as a prior estimate the national anthropogenic emission inventories for the three countries reported by the US Environmental Protection Agency (EPA), Environment and Climate Change Canada (ECCC), and the Instituto Nacional de Ecología y Cambio Climático (INECC) in Mexico to the United Nations Framework Convention on Climate Change (UNFCCC) and thus serves as an evaluation of these inventories in terms of their magnitudes and trends. Emissions are optimized with a Gaussian mixture model (GMM) at 0.5∘×0.625∘ resolution and for individual years. Optimization is done analytically using lognormal error forms. This yields closed-form statistics of error covariances and information content on the posterior (optimized) estimates, allows better representation of the high tail of the emission distribution, and enables construction of a large ensemble of inverse solutions using different observations and assumptions. We find that GOSAT and in situ observations are largely consistent and complementary in the optimization of methane emissions for North America. Mean 2010–2017 anthropogenic emissions from our base GOSAT + in situ inversion, with ranges from the inversion ensemble, are 36.9 (32.5–37.8) Tg a−1 for CONUS, 5.3 (3.6–5.7) Tg a−1 for Canada, and 6.0 (4.7–6.1) Tg a−1 for Mexico. These are higher than the most recent reported national inventories of 26.0 Tg a−1 for the US (EPA), 4.0 Tg a−1 for Canada (ECCC), and 5.0 Tg a−1 for Mexico (INECC). The correction in all three countries is largely driven by a factor of 2 underestimate in emissions from the oil sector with major contributions from the south-central US, western Canada, and southeastern Mexico. Total CONUS anthropogenic emissions in our inversion peak in 2014, in contrast to the EPA report of a steady decreasing trend over 2010–2017. This reflects offsetting effects of increasing emissions from the oil and landfill sectors, decreasing emissions from the gas sector, and flat emissions from the livestock and coal sectors. We find decreasing trends in Canadian and Mexican anthropogenic methane emissions over the 2010–2017 period, mainly driven by oil and gas emissions. Our best estimates of mean 2010–2017 wetland emissions are 8.4 (6.4–10.6) Tg a−1 for CONUS, 9.9 (7.8–12.0) Tg a−1 for Canada, and 0.6 (0.4–0.6) Tg a−1 for Mexico. Wetland emissions in CONUS show an increasing trend of +2.6 (+1.7 to +3.8)% a−1 over 2010–2017 correlated with precipitation.

M
Ma, Dianyan, Jianchun Bian, Dan Li, Zhixuan Bai, Qian Li, Jinqiang Zhang, Haoyue Wang, Xiangdong Zheng, Dale F. Hurst and Holger Vömel, (2022), Mixing characteristics within the tropopause transition layer over the Asian summer monsoon region based on ozone and water vapor sounding data, Atmospheric Research, 271, 106093, 10.1016/j.atmosres.2022.106093

Abstract

The structure of the tropopause transition layer (TTL) over the Asian summer monsoon (ASM) anticyclone is analyzed on the basis of high-resolution balloon soundings of temperature, ozone, and water vapor at Kunming and Lhasa, China during 11 summer monsoon seasons between 2009 and 2019. Two definitions of the TTL, one based on thermal structure and one based on tracer correlations of O3 and H2O, are analyzed and compared. In tracer–tracer space, the air masses of mixed stratospheric and tropospheric characteristics are identified by using the O3–H2O correlations. The mixed air formed a transitional layer and shows strong spatial variation in the altitude space. Statistical result shows that the altitude range of mixed air parcels spans a layer of approximately 5.5 km depth between 12.5 km and 18 km. This vertical distribution of mixed air masses is basically consistent with thermally-based TTL, which takes the level of minimum stability (LMS) and the cold point tropopause (CPT) as its lower and upper boundaries, respectively. The thermal definition regards the TTL as a thermal transition zone, but does not consider the tracer mixing features between stratosphere and troposphere. Tracer correlations can identify the mixed air mass, which is a basic feature of the TTL, whether they are from the range of the thermally-based TTL, or below the LMS, or above the CPT. Based on the O3–H2O correlations, statistical analysis shows that about 30%–50% of air masses between the LMS and the CPT are identified as mixed. And up to 1–1.5 km above the CPT, a small fraction of air masses is also mixed, which means that air masses from the troposphere can be lifted and mixed into the free stratosphere within the ASM anticyclone region.

Malone, Sparkle L., Youmi Oh, Kyle A. Arndt, George Burba, Roisin Commane, Alexandra R. Contosta, Jordan P. Goodrich, Henry W. Loescher, Gregory Starr and Ruth K. Varner, (2022), Gaps in network infrastructure limit our understanding of biogenic methane emissions for the United States, Biogeosciences, 19, 9, 2507-2522, 10.5194/bg-19-2507-2022

Abstract

Abstract. Understanding the sources and sinks of methane (CH4) is critical to both predicting and mitigating future climate change. There are large uncertainties in the global budget of atmospheric CH4, but natural emissions are estimated to be of a similar magnitude to anthropogenic emissions. To understand CH4 flux from biogenic sources in the United States (US) of America, a multi-scale CH4 observation network focused on CH4 flux rates, processes, and scaling methods is required. This can be achieved with a network of ground-based observations that are distributed based on climatic regions and land cover. To determine the gaps in physical infrastructure for developing this network, we need to understand the landscape representativeness of the current infrastructure. We focus here on eddy covariance (EC) flux towers because they are essential for a bottom-up framework that bridges the gap between point-based chamber measurements and airborne or satellite platforms that inform policy decisions and global climate agreements. Using dissimilarity, multidimensional scaling, and cluster analysis, the US was divided into 10 clusters distributed across temperature and precipitation gradients. We evaluated dissimilarity within each cluster for research sites with active CH4 EC towers to identify gaps in existing infrastructure that limit our ability to constrain the contribution of US biogenic CH4 emissions to the global budget. Through our analysis using climate, land cover, and location variables, we identified priority areas for research infrastructure to provide a more complete understanding of the CH4 flux potential of ecosystem types across the US. Clusters corresponding to Alaska and the Rocky Mountains, which are inherently difficult to capture, are the most poorly represented, and all clusters require a greater representation of vegetation types.

Michalsky, Joseph J. and Peter W. Kiedron, (2022), Moderate spectral resolution solar irradiance measurements, aerosol optical depth, and solar transmission, from 360 to 1070 nm, using the refurbished rotating shadow band spectroradiometer (RSS), Atmospheric Measurement Techniques, 15, 2, 353-364, 10.5194/amt-15-353-2022

Abstract

Abstract. This paper reports on a third-generation rotating shadow band spectroradiometer (RSS) used to measure global and diffuse horizontal plus direct normal irradiances and transmissions at 1002 wavelengths between 360 and 1070 nm. The prism-dispersed spectral data are from the Atmospheric Radiation Measurement (ARM) Southern Great Plains site in north-central Oklahoma (36.605∘ N, 97.486∘ W) and cover dates between August 2009 and February 2014. The refurbished RSS isolates the detector in a vacuum chamber with pressures near 10−7 torr. This prevents the deposition of outgassed vapors from the interior of the spectrometer shell on the cooled detector that affected the operation of the first commercial RSS. Methods for (1) ensuring the correct wavelength registration of the data and (2) deriving extraterrestrial responses over the entire spectrum, including throughout strong water vapor and oxygen bands, are described. The resulting data produced are archived as ARM data records and include cloud-screened aerosol optical depths, spectral irradiances and direct normal solar transmission, as well as normalized diffuse and global irradiances.

Miner, Kimberley R., Merritt R. Turetsky, Edward Malina, Annett Bartsch, Johanna Tamminen, A. David McGuire, Andreas Fix, Colm Sweeney, Clayton D. Elder and Charles E. Miller, (2022), Permafrost carbon emissions in a changing Arctic, Nature Reviews Earth & Environment, 3, 1, 55-67, 10.1038/s43017-021-00230-3

Abstract

Arctic permafrost stores nearly 1,700 billion metric tons of frozen and thawing carbon. Anthropogenic warming threatens to release an unknown quantity of this carbon to the atmosphere, influencing the climate in processes collectively known as the permafrost carbon feedback. In this Review, we discuss advances in tracking permafrost carbon dynamics, including mechanisms of abrupt thaw, instrumental observations of carbon release and model predictions of the permafrost carbon feedback. Abrupt thaw and thermokarst could emit a substantial amount of carbon to the atmosphere rapidly (days to years), mobilizing the deep legacy carbon sequestered in Yedoma. Carbon dioxide emissions are proportionally larger than other greenhouse gas emissions in the Arctic, but expansion of anoxic conditions within thawed permafrost and soils stands to increase the proportion of future methane emissions. Increasingly frequent wildfires in the Arctic will also lead to a notable but unpredictable carbon flux. More detailed monitoring though in situ, airborne and satellite observations will provide a deeper understanding of the Arctic s future role as a carbon source or sink, and the subsequent impact on the Earth system. Large stores of carbon could be released to the atmosphere from Arctic warming, driving permafrost thaw. This Review examines the processes that impact Arctic permafrost carbon emissions, how they might change in the future and ways to monitor and predict these changes.

N
Nicewonger, M. R., Eric S. Saltzman and S. A. Montzka, (2022), ENSO‐Driven Fires Cause Large Interannual Variability in the Naturally Emitted, Ozone‐Depleting Trace Gas CHBr, Geophysical Research Letters, 49, 3, 10.1029/2021GL094756

Abstract

Methyl bromide (CH3Br) is an ozone depleting trace gas that is now mainly emitted from natural sources. Roughly 80% of anthropogenic production of CH3Br was phased-out in response to the Montreal Protocol on Substances that Deplete the Ozone Layer beginning in 1999 and atmospheric levels of CH3Br have declined considerably since. Here we use surface measurements of CH3Br from NOAA's global air sampling network, along with a six-box atmosphere/ocean model to explore interannual variability in atmospheric CH3Br mole fractions. We find that CH3Br mole fractions are strongly correlated with the El Niño Southern Oscillation (ENSO) phenomenon, but variability in winds, sea surface temperature, and biological production during ENSO are unlikely to drive the observed changes in atmospheric CH3Br directly. Rather, the results indicate that ENSO-driven changes to biomass burning are an important cause of the observed interannual CH3Br variability.

O
Oh, Youmi, Qianlai Zhuang, Lisa R. Welp, Licheng Liu, Xin Lan, Sourish Basu, Edward J. Dlugokencky, Lori Bruhwiler, John B. Miller, Sylvia E. Michel, Stefan Schwietzke, Pieter Tans, Philippe Ciais and Jeffrey P. Chanton, (2022), Improved global wetland carbon isotopic signatures support post-2006 microbial methane emission increase, Communications Earth & Environment, 3, 1, 10.1038/s43247-022-00488-5

Abstract

Atmospheric concentrations of methane, a powerful greenhouse gas, have strongly increased since 2007. Measurements of stable carbon isotopes of methane can constrain emissions if the isotopic compositions are known; however, isotopic compositions of methane emissions from wetlands are poorly constrained despite their importance. Here, we use a process-based biogeochemistry model to calculate the stable carbon isotopic composition of global wetland methane emissions. We estimate a mean global signature of −61.3 ± 0.7‰ and find that tropical wetland emissions are enriched by ~11‰ relative to boreal wetlands. Our model shows improved resolution of regional, latitudinal and global variations in isotopic composition of wetland emissions. Atmospheric simulation scenarios with the improved wetland isotopic composition suggest that increases in atmospheric methane since 2007 are attributable to rising microbial emissions. Our findings substantially reduce uncertainty in the stable carbon isotopic composition of methane emissions from wetlands and improve understanding of the global methane budget.

Ouimette, James R., William C. Malm, Bret A. Schichtel, Patrick J. Sheridan, Elisabeth Andrews, John A. Ogren and W. Patrick Arnott, (2022), Evaluating the PurpleAir monitor as an aerosol light scattering instrument, Atmospheric Measurement Techniques, 15, 3, 655-676, 10.5194/amt-15-655-2022

Abstract

Abstract. The Plantower PMS5003 sensors (PMS) used in the PurpleAir monitor PA-II-SD configuration (PA-PMS) are equivalent to cell-reciprocal nephelometers using a 657 nm perpendicularly polarized light source that integrates light scattering from 18 to 166∘. Yearlong field data at the National Oceanic and Atmospheric Administration's (NOAA) Mauna Loa Observatory (MLO) and Boulder Table Mountain (BOS) sites show that the 1 h average of the PA-PMS first size channel, labeled “> 0.3 µm” (“CH1”), is highly correlated with submicrometer aerosol scattering coefficients at the 550 and 700 nm wavelengths measured by the TSI 3563 integrating nephelometer, from 0.4 to 500 Mm−1. This corresponds to an hourly average submicrometer aerosol mass concentration of approximately 0.2 to 200 µg m−3. A physical–optical model of the PMS is developed to estimate light intensity on the photodiode, accounting for angular truncation of the volume scattering function as a function of particle size. The model predicts that the PMS response to particles > 0.3 µm decreases relative to an ideal nephelometer by about 75 % for particle diameters ≥ 1.0 µm. This is a result of using a laser that is polarized, the angular truncation of the scattered light, and particle losses (e.g., due to aspiration) before reaching the laser. It is shown that CH1 is linearly proportional to the model-predicted intensity of the light scattered by particles in the PMS laser to its photodiode over 4 orders of magnitude. This is consistent with CH1 being a measure of the scattering coefficient and not the particle number concentration or particulate matter concentration. The model predictions are consistent with data from published laboratory studies which evaluated the PMS against a variety of aerosols. Predictions are then compared with yearlong fine aerosol size distribution and scattering coefficient field data at the BOS site. Field data at BOS confirm the model prediction that the ratio of CH1 to the scattering coefficient would be highest for aerosols with median scattering diameters < 0.3 µm. The PMS detects aerosols smaller than 0.3 µm diameter in proportion to their contribution to the scattering coefficient. The results of this study indicate that the PMS is not an optical particle counter and that its six size fractions are not a meaningful representation of particle size distribution. The relationship between the PMS 1 h average CH1 and bsp1, the scattering coefficient in Mm−1 due to particles below 1 µm aerodynamic diameter, at wavelength 550 nm, is found to be bsp1 = 0.015 ± 2.07 × 10−5 × CH1, for relative humidity below 40 %. The coefficient of determination r2 is 0.97. This suggests that the low-cost and widely used PA monitors can be used to measure and predict the submicron aerosol light scattering coefficient in the mid-visible nearly as well as integrating nephelometers. The effectiveness of the PA-PMS to serve as a PM2.5 mass concentration monitor is due to both the sensor behaving like an imperfect integrating nephelometer and the mass scattering efficiency of ambient PM2.5 aerosols being roughly constant.

P
PATRA, Prabir K., Edward J. DLUGOKENCKY, James W. ELKINS, Geoff S. DUTTON, Yasunori TOHJIMA, Motoki SASAKAWA, Akihiko ITO, Ray F. WEISS, Manfredi MANIZZA, Paul B. KRUMMEL, Ronald G. PRINN, Simon O'DOHERTY, Daniele BIANCHI, Cynthia NEVISON, Efisio SOLAZZO, Haeyoung LEE, Sangwon JOO, Eric A. KORT, Suman MAITY and Masayuki TAKIGAWA, (2022), Forward and Inverse Modelling of Atmospheric Nitrous Oxide Using MIROC4-Atmospheric Chemistry-Transport Model, Journal of the Meteorological Society of Japan. Ser. II, 100, 2, 361-386, 10.2151/jmsj.2022-018

Abstract

Atmospheric nitrous oxide (N2O) contributes to global warming and stratospheric ozone depletion, so reducing uncertainty in estimates of emissions from different sources is important for climate policy. Here, we simulate atmospheric N2O using an atmospheric chemistry-transport model (ACTM), and the results are first compared with the in situ measurements. Five combinations of known (a priori) N2O emissions due to natural soil, agricultural land, other human activities and sea-air exchange are used. The N2O lifetime is 127.6 ± 4.0 yr in the control ACTM simulation (range indicate interannual variability). Regional N2O emissions are optimised by Bayesian inverse modelling for 84 partitions of the globe at monthly intervals, using measurements at 42 sites around the world covering 1997-2019. The best estimate global land and ocean emissions are 12.99 ± 0.22 and 2.74 ± 0.27 TgN yr−1, respectively, for 2000-2009, and 14.30 ± 0.20 and 2.91 ± 0.27 TgN yr−1, respectively, for 2010-2019. On regional scales, we find that the most recent ocean emission estimation, with lower emissions in the Southern Ocean regions, fits better with that predicted by the inversions. Marginally higher (lower) emissions than the inventory/model for the tropical (extra-tropical) land regions is estimated and validated using independent aircraft observations. Global land and ocean emission variabilities show statistically significant correlation with El Niño Southern Oscillation (ENSO). Analysis of regional land emissions shows increases over America (Temperate North, Central, Tropical), Central Africa, and Asia (South, East and Southeast) between the 2000s and 2010s. Only Europe as a whole recorded a slight decrease in N2O emissions due to chemical industry. Our inversions suggest revisions to seasonal emission variations for 3 of the 15 land regions (East Asia, Temperate North America and Central Africa), and the Southern Ocean region. The terrestrial ecosystem model (VISIT) is able to simulate annual total emissions in agreement with the observed N2O growth rate since 1978, but the lag-time scales of N2O emissions from nitrogen fertiliser application may need to be revised.

Petropavlovskikh, Irina, Koji Miyagawa, Audra McClure-Beegle, Bryan Johnson, Jeannette Wild, Susan Strahan, Krzysztof Wargan, Richard Querel, Lawrence Flynn, Eric Beach, Gerard Ancellet and Sophie Godin-Beekmann, (2022), Optimized Umkehr profile algorithm for ozone trend analyses, Atmospheric Measurement Techniques, 15, 6, 1849-1870, 10.5194/amt-15-1849-2022

Abstract

Abstract. The long-term record of Umkehr measurements from four NOAA Dobson spectrophotometers was reprocessed after updates to the instrument calibration procedures. In addition, a new data quality-control tool was developed for the Dobson automation software (WinDobson). This paper presents a comparison of Dobson Umkehr ozone profiles from NOAA ozone network stations – Boulder, the Haute-Provence Observatory (OHP), the Mauna Loa Observatory (MLO), Lauder – against several satellite records, including Aura Microwave Limb Sounder (MLS; ver. 4.2), and combined solar backscatter ultraviolet (SBUV) and Ozone Mapping and Profiler Suite (OMPS) records (NASA aggregated and NOAA cohesive datasets). A subset of satellite data is selected to match Dobson Umkehr observations at each station spatially (distance less than 200 km) and temporally (within 24 h). Umkehr Averaging kernels (AKs) are applied to vertically smooth all overpass satellite profiles prior to comparisons. The station Umkehr record consists of several instrumental records, which have different optical characterizations, and thus instrument-specific stray light contributes to the data processing errors and creates step changes in the record. This work evaluates the overall quality of Umkehr long-term measurements at NOAA ground-based stations and assesses the impact of the instrumental changes on the stability of the Umkehr ozone profile record. This paper describes a method designed to correct biases and discontinuities in the retrieved Umkehr profile that originate from the Dobson calibration process, repair, or optical realignment of the instrument. The Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA-2) Global Modeling Initiative (M2GMI) and NASA Global Modeling Initiative chemistry transport model (GMI CTM) ozone profile model output matched to station location and date of observation is used to evaluate instrumental step changes in the Umkehr record. Homogenization of the Umkehr record and discussion of the apparent stray light error in retrieved ozone profiles are the focus of this paper. Homogenization of ground-based records is of great importance for studies of long-term ozone trends and climate change.

R
Read, William G., Gabriele Stiller, Stefan Lossow, Michael Kiefer, Farahnaz Khosrawi, Dale Hurst, Holger Vömel, Karen Rosenlof, Bianca M. Dinelli, Piera Raspollini, Gerald E. Nedoluha, John C. Gille, Yasuko Kasai, Patrick Eriksson, Christopher E. Sioris, Kaley A. Walker, Katja Weigel, John P. Burrows and Alexei Rozanov, (2022), The SPARC Water Vapor Assessment II: assessment of satellite measurements of upper tropospheric humidity, Atmospheric Measurement Techniques, 15, 11, 3377-3400, 10.5194/amt-15-3377-2022

Abstract

Abstract. Nineteen limb-viewing data sets (occultation, passive thermal, and UV scattering) and two nadir upper tropospheric humidity (UTH) data sets are intercompared and also compared to frost-point hygrometer balloon sondes. The upper troposphere considered here covers the pressure range from 300–100 hPa. UTH is a challenging measurement, because concentrations vary between 2–1000 ppmv (parts per million by volume), with sharp changes in vertical gradients near the tropopause. Cloudiness in this region also makes the measurement challenging. The atmospheric temperature is also highly variable ranging from 180–250 K. The assessment of satellite-measured UTH is based on coincident comparisons with balloon frost-point hygrometer sondes, multi-month mapped comparisons, zonal mean time series comparisons, and coincident satellite-to-satellite comparisons. While the satellite fields show similar features in maps and time series, quantitatively they can differ by a factor of 2 in concentration, with strong dependencies on the amount of UTH. Additionally, time-lag response-corrected Vaisala RS92 radiosondes are compared to satellites and the frost-point hygrometer measurements. In summary, most satellite data sets reviewed here show on average ∼30 % agreement amongst themselves and frost-point data but with an additional ∼30 % variability about the mean bias. The Vaisala RS92 sonde, even with a time-lag correction, shows poor behavior for pressures less than 200 hPa.

S
Saltzman, E. S., M. R. Nicewonger, S. A. Montzka and S. A. Yvon‐Lewis, (2022), A Post‐Phaseout Retrospective Reassessment of the Global Methyl Bromide Budget, Journal of Geophysical Research: Atmospheres, 127, 3, 10.1029/2021JD035567

Abstract

Methyl bromide is a stratospheric ozone-depleting substance with both natural and anthropogenic sources. The global budget of methyl bromide has never been fully understood as evidenced by the significant budget gap between the bottom-up source estimates and calculated atmospheric losses. Atmospheric methyl bromide levels have declined significantly since Phase-out under the Montreal Protocol began in 1999, and the atmosphere appears to have reached a new steady state during the past five years. Here, we reassess the global methyl bromide budget utilizing the 25-year record of atmospheric methyl bromide measurements from the National Oceanic and Atmospheric Administration Global Monitoring Laboratory global flask network and a zonal 6-box coupled global ocean/atmosphere model. Model inversions were used to estimate the total emissions required to account for the observed atmospheric methyl bromide levels. From 1995 to 2019, global land-based emissions (natural and anthropogenic) declined from about 120 to 85 Gg y−1 and net ocean emissions increased from −5 to +5 Gg y−1. There remains an imbalance between the bottom-up estimates of terrestrial sources and the inversion result. Based on the timing, magnitude, and spatial distribution of the imbalance we partition it into (a) a persistent or time invariant source located primarily in the tropics, and (b) a smaller time-varying component that scales with the anthropogenic source during phase-out. We hypothesize that the persistent source is likely natural and the time variant component is an artifact resulting from a slight underestimation of anthropogenic emissions.

Schmale, Julia, Sangeeta Sharma, Stefano Decesari, Jakob Pernov, Andreas Massling, Hans-Christen Hansson, Knut von Salzen, Henrik Skov, Elisabeth Andrews, Patricia K. Quinn, Lucia M. Upchurch, Konstantinos Eleftheriadis, Rita Traversi, Stefania Gilardoni, Mauro Mazzola, James Laing and Philip Hopke, (2022), Pan-Arctic seasonal cycles and long-term trends of aerosol properties from 10 observatories, Atmospheric Chemistry and Physics, 22, 5, 3067-3096, 10.5194/acp-22-3067-2022

Abstract

Abstract. Even though the Arctic is remote, aerosol properties observed there are strongly influenced by anthropogenic emissions from outside the Arctic. This is particularly true for the so-called Arctic haze season (January through April). In summer (June through September), when atmospheric transport patterns change, and precipitation is more frequent, local Arctic sources, i.e., natural sources of aerosols and precursors, play an important role. Over the last few decades, significant reductions in anthropogenic emissions have taken place. At the same time a large body of literature shows evidence that the Arctic is undergoing fundamental environmental changes due to climate forcing, leading to enhanced emissions by natural processes that may impact aerosol properties. In this study, we analyze 9 aerosol chemical species and 4 particle optical properties from 10 Arctic observatories (Alert, Kevo, Pallas, Summit, Thule, Tiksi, Barrow/Utqiaġvik, Villum, and Gruvebadet and Zeppelin Observatory – both at Ny-Ålesund Research Station) to understand changes in anthropogenic and natural aerosol contributions. Variables include equivalent black carbon, particulate sulfate, nitrate, ammonium, methanesulfonic acid, sodium, iron, calcium and potassium, as well as scattering and absorption coefficients, single scattering albedo and scattering Ångström exponent. First, annual cycles are investigated, which despite anthropogenic emission reductions still show the Arctic haze phenomenon. Second, long-term trends are studied using the Mann–Kendall Theil–Sen slope method. We find in total 41 significant trends over full station records, i.e., spanning more than a decade, compared to 26 significant decadal trends. The majority of significantly declining trends is from anthropogenic tracers and occurred during the haze period, driven by emission changes between 1990 and 2000. For the summer period, no uniform picture of trends has emerged. Twenty-six percent of trends, i.e., 19 out of 73, are significant, and of those 5 are positive and 14 are negative. Negative trends include not only anthropogenic tracers such as equivalent black carbon at Kevo, but also natural indicators such as methanesulfonic acid and non-sea-salt calcium at Alert. Positive trends are observed for sulfate at Gruvebadet. No clear evidence of a significant change in the natural aerosol contribution can be observed yet. However, testing the sensitivity of the Mann–Kendall Theil–Sen method, we find that monotonic changes of around 5 % yr−1 in an aerosol property are needed to detect a significant trend within one decade. This highlights that long-term efforts well beyond a decade are needed to capture smaller changes. It is particularly important to understand the ongoing natural changes in the Arctic, where interannual variability can be high, such as with forest fire emissions and their influence on the aerosol population. To investigate the climate-change-induced influence on the aerosol population and the resulting climate feedback, long-term observations of tracers more specific to natural sources are needed, as well as of particle microphysical properties such as size distributions, which can be used to identify changes in particle populations which are not well captured by mass-oriented methods such as bulk chemical composition.

Sedlar, J., L. D. Riihimaki, D. D. Turner, J. Duncan, B. Adler, L. Bianco, K. Lantz, J. Wilczak, E. Hall, C. Herrera and Gary B. Hodges, (2022), Investigating the Impacts of Daytime Boundary Layer Clouds on Surface Energy Fluxes and Boundary Layer Structure During CHEESEHEAD19, Journal of Geophysical Research: Atmospheres, 127, 5, 10.1029/2021JD036060

Abstract

Studies of land-atmosphere interactions under a clear sky and low cumulus cloud conditions are common from long-term observatories like at the southern great plains. How well the relationships and responses of surface radiative and turbulent heat fluxes determined from these investigations hold for more heterogeneous surfaces in other climate regimes, however, is uncertain. In this study, detailed observations of the surface energy budget and daytime boundary layer properties are analyzed using measurements from the Chequamegon Heterogenous Ecosystem Energy-Balance Study Enabled by a High-Density Extensive Array of Detectors 2019 (CHEESEHEAD19) field campaign, July-October 2019, across a heterogeneous forested landscape of northern Wisconsin. A cloud regime framework is employed to classify consecutive periods of clear skies from lower atmosphere stratiform and cumulus clouds. A seasonal transition from low cumulus to low stratiform periods occurred, together with a diurnal pattern in cloudy or clear sky period dominance. Radiative forcing was highly dependent on sky conditions, leading to changes in the redistribution efficiency of radiative energy by the surface turbulent heat fluxes. During CHEESEHEAD19, small Bowen ratios dominated with daytime latent heat fluxes three times as large as sensible heat fluxes for all sky conditions studied; the forested region, therefore, falls within an energy-limited regime. The depth of the daytime mixed layer depended upon the sky condition and thermodynamic setting; deeper mixed layers occurred during periods of low cumulus and not clear skies. Profiles of vertical velocity were found to have enhanced variance under low cumulus compared to clear sky periods, suggesting potential for cloud feedbacks on boundary layer structure and surface energy fluxes.

Sterzinger, Lucas J., Joseph Sedlar, Heather Guy, Ryan R. Neely III and Adele L. Igel, (2022), Do Arctic mixed-phase clouds sometimes dissipate due to insufficient aerosol? Evidence from comparisons between observations and idealized simulations, Atmospheric Chemistry and Physics, 22, 13, 8973-8988, 10.5194/acp-22-8973-2022

Abstract

Abstract. Mixed-phase clouds are ubiquitous in the Arctic. These clouds can persist for days and dissipate in a matter of hours. It is sometimes unknown what causes this sudden dissipation, but aerosol–cloud interactions may be involved. Arctic aerosol concentrations can be low enough to affect cloud formation and structure, and it has been hypothesized that, in some instances, concentrations can drop below some critical value needed to maintain a cloud. We use observations from a Department of Energy ARM site on the northern slope of Alaska at Oliktok Point (OLI), the Arctic Summer Cloud Ocean Study (ASCOS) field campaign in the high Arctic Ocean, and the Integrated Characterisation of Energy, Clouds, Atmospheric state, and Precipitation at Summit – Aerosol Cloud Experiment (ICECAPS-ACE) project at the NSF (National Science Foundation) Summit Station in Greenland (SMT) to identify one case per site where Arctic boundary layer clouds dissipated coincidentally with a decrease in surface aerosol concentrations. These cases are used to initialize idealized large eddy simulations (LESs) in which aerosol concentrations are held constant until, at a specified time, all aerosols are removed instantaneously – effectively creating an extreme case of aerosol-limited dissipation which represents the fastest a cloud could possibly dissipate via this process. These LESs are compared against the observed data to determine whether cases could, potentially, be dissipating due to insufficient aerosol. The OLI case's observed liquid water path (LWP) dissipated faster than its simulation, indicating that other processes are likely the primary drivers of the dissipation. The ASCOS and SMT observed LWP dissipated at similar rates to their respective simulations, suggesting that aerosol-limited dissipation may be occurring in these instances. We also find that the microphysical response to this extreme aerosol forcing depends greatly on the specific case being simulated. Cases with drizzling liquid layers are simulated to dissipate by accelerating precipitation when aerosol is removed while the case with a non-drizzling liquid layer dissipates quickly, possibly glaciating via the Wegener–Bergeron–Findeisen (WBF) process. The non-drizzling case is also more sensitive to ice-nucleating particle (INP) concentrations than the drizzling cases. Overall, the simulations suggest that aerosol-limited cloud dissipation in the Arctic is plausible and that there are at least two microphysical pathways by which aerosol-limited dissipation can occur.

T
Thompson, Chelsea R., Steven C. Wofsy, Michael J. Prather, Paul A. Newman, Thomas F. Hanisco, Thomas B. Ryerson, David W. Fahey, Eric C. Apel, Charles A. Brock, William H. Brune, Karl Froyd, Joseph M. Katich, Julie M. Nicely, Jeff Peischl, Eric Ray, Patrick R. Veres, Siyuan Wang, Hannah M. Allen, Elizabeth Asher, Huisheng Bian, Donald Blake, Ilann Bourgeois, John Budney, T. Paul Bui, Amy Butler, Pedro Campuzano-Jost, Cecilia Chang, Mian Chin, Róisín Commane, Gus Correa, John D. Crounse, Bruce Daube, Jack E. Dibb, Joshua P. DiGangi, Glenn S. Diskin, Maximilian Dollner, James W. Elkins, Arlene M. Fiore, Clare M. Flynn, Hao Guo, Samuel R. Hall, Reem A. Hannun, Alan Hills, Eric J. Hintsa, Alma Hodzic, Rebecca S. Hornbrook, L. Greg Huey, Jose L. Jimenez, Ralph F. Keeling, Michelle J. Kim, Agnieszka Kupc, Forrest Lacey, Leslie R. Lait, Jean-Francois Lamarque, Junhua Liu, Kathryn McKain, Simone Meinardi, David O. Miller, Stephen A. Montzka, Fred L. Moore, Eric J. Morgan, Daniel M. Murphy, Lee T. Murray, Benjamin A. Nault, J. Andrew Neuman, Louis Nguyen, Yenny Gonzalez, Andrew Rollins, Karen Rosenlof, Maryann Sargent, Gregory Schill, Joshua P. Schwarz, Jason M. St. Clair, Stephen D. Steenrod, Britton B. Stephens, Susan E. Strahan, Sarah A. Strode, Colm Sweeney, Alexander B. Thames, Kirk Ullmann, Nicholas Wagner, Rodney Weber, Bernadett Weinzierl, Paul O. Wennberg, Christina J. Williamson, Glenn M. Wolfe and Linghan Zeng, (2022), The NASA Atmospheric Tomography (ATom) Mission: Imaging the Chemistry of the Global Atmosphere, Bulletin of the American Meteorological Society, 103, 3, E761-E790, 10.1175/BAMS-D-20-0315.1

Abstract

This article provides an overview of the NASA Atmospheric Tomography (ATom) mission and a summary of selected scientific findings to date. ATom was an airborne measurements and modeling campaign aimed at characterizing the composition and chemistry of the troposphere over the most remote regions of the Pacific, Southern, Atlantic, and Arctic Oceans, and examining the impact of anthropogenic and natural emissions on a global scale. These remote regions dominate global chemical reactivity and are exceptionally important for global air quality and climate. ATom data provide the in situ measurements needed to understand the range of chemical species and their reactions, and to test satellite remote sensing observations and global models over large regions of the remote atmosphere. Lack of data in these regions, particularly over the oceans, has limited our understanding of how atmospheric composition is changing in response to shifting anthropogenic emissions and physical climate change. ATom was designed as a global-scale tomographic sampling mission with extensive geographic and seasonal coverage, tropospheric vertical profiling, and detailed speciation of reactive compounds and pollution tracers. ATom flew the NASA DC-8 research aircraft over four seasons to collect a comprehensive suite of measurements of gases, aerosols, and radical species from the remote troposphere and lower stratosphere on four global circuits from 2016 to 2018. Flights maintained near-continuous vertical profiling of 0.15–13-km altitudes on long meridional transects of the Pacific and Atlantic Ocean basins. Analysis and modeling of ATom data have led to the significant early findings highlighted here.

Tribby, Ariana L., Justin S. Bois, Stephen A. Montzka, Elliot L. Atlas, Isaac Vimont, Xin Lan, Pieter P. Tans, James W. Elkins, Donald R. Blake and Paul O. Wennberg, (2022), Hydrocarbon Tracers Suggest Methane Emissions from Fossil Sources Occur Predominately Before Gas Processing and That Petroleum Plays Are a Significant Source, Environmental Science & Technology, 56, 13, 9623-9631, 10.1021/acs.est.2c00927

Abstract

We use global airborne observations of propane (C3H8) and ethane (C2H6) from the Atmospheric Tomography (ATom) and HIAPER Pole-to-Pole Observations (HIPPO), as well as U.S.-based aircraft and tower observations by NOAA and from the NCAR FRAPPE campaign as tracers for emissions from oil and gas operations. To simulate global mole fraction fields for these gases, we update the default emissions’ configuration of C3H8 used by the global chemical transport model, GEOS-Chem v13.0.0, using a scaled C2H6 spatial proxy. With the updated emissions, simulations of both C3H8 and C2H6 using GEOS-Chem are in reasonable agreement with ATom and HIPPO observations, though the updated emission fields underestimate C3H8 accumulation in the arctic wintertime, pointing to additional sources of this gas in the high latitudes (e.g., Europe). Using a Bayesian hierarchical model, we estimate global emissions of C2H6 and C3H8 from fossil fuel production in 2016–2018 to be 13.3 ± 0.7 (95% CI) and 14.7 ± 0.8 (95% CI) Tg/year, respectively. We calculate bottom-up hydrocarbon emission ratios using basin composition measurements weighted by gas production and find their magnitude is higher than expected and is similar to ratios informed by our revised alkane emissions. This suggests that emissions are dominated by pre-processing activities in oil-producing basins.

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Velders, Guus J. M., John S. Daniel, Stephen A. Montzka, Isaac Vimont, Matthew Rigby, Paul B. Krummel, Jens Muhle, Simon O'Doherty, Ronald G. Prinn, Ray F. Weiss and Dickon Young, (2022), Projections of hydrofluorocarbon (HFC) emissions and the resulting global warming based on recent trends in observed abundances and current policies, Atmospheric Chemistry and Physics, 22, 9, 6087-6101, 10.5194/acp-22-6087-2022

Abstract

Abstract. The emissions of hydrofluorocarbons (HFCs) have increased significantly in the past 2 decades, primarily as a result of the phaseout of ozone-depleting substances under the Montreal Protocol and the use of HFCs as their replacements. In 2015, large increases were projected in HFC use and emissions in this century in the absence of regulations, contributing up to 0.5 ∘C to global surface warming by 2100. In 2019, the Kigali Amendment to the Montreal Protocol came into force with the goal of limiting the use of HFCs globally, and currently, regulations to limit the use of HFCs are in effect in several countries. Here, we analyze trends in HFC emissions inferred from observations of atmospheric abundances and compare them with previous projections. Total CO2 eq. inferred HFC emissions continue to increase through 2019 (to about 0.8 GtCO2eq.yr-1) but are about 20 % lower than previously projected for 2017–2019, mainly because of the lower global emissions of HFC-143a. This indicates that HFCs are used much less in industrial and commercial refrigeration (ICR) applications than previously projected. This is supported by data reported by the developed countries and the lower reported consumption of HFC-143a in China. Because this time period preceded the beginning of the Kigali provisions, this reduction cannot be linked directly to the provisions of the Kigali Amendment. However, it could indicate that companies transitioned away from the HFC-143a with its high global warming potential (GWP) for ICR applications in anticipation of national or global mandates. There are two new HFC scenarios developed based (1) on current trends in HFC use and Kigali-independent (K-I) control policies currently existing in several countries and (2) current HFC trends and compliance with the Kigali Amendment (KA-2022). These current policies reduce projected emissions in 2050 from the previously calculated 4.0–5.3 GtCO2eq.yr-1 to 1.9–3.6 GtCO2eq.yr-1. The added provisions of the Kigali Amendment are projected to reduce the emissions further to 0.9–1.0 GtCO2eq.yr-1 in 2050. Without any controls, projections suggest a HFC contribution of 0.28–0.44 ∘C to global surface warming by 2100, compared to a temperature contribution of 0.14–0.31 ∘C that is projected considering the national K-I policies current in place. Warming from HFCs is additionally limited by the Kigali Amendment controls to a contribution of about 0.04 ∘C by 2100.

Virkkula, Aki, Henrik Grythe, John Backman, Tuukka Petäjä, Maurizio Busetto, Christian Lanconelli, Angelo Lupi, Silvia Becagli, Rita Traversi, Mirko Severi, Vito Vitale, Patrick Sheridan and Elisabeth Andrews, (2022), Aerosol optical properties calculated from size distributions, filter samples and absorption photometer data at Dome C, Antarctica, and their relationships with seasonal cycles of sources, Atmospheric Chemistry and Physics, 22, 7, 5033-5069, 10.5194/acp-22-5033-2022

Abstract

Abstract. Optical properties of surface aerosols at Dome C, Antarctica, in 2007–2013 and their potential source areas are presented. Scattering coefficients (σsp) were calculated from measured particle number size distributions with a Mie code and from filter samples using mass scattering efficiencies. Absorption coefficients (σap) were determined with a three-wavelength Particle Soot Absorption Photometer (PSAP) and corrected for scattering by using two different algorithms. The scattering coefficients were also compared with σsp measured with a nephelometer at the South Pole Station (SPO). The minimum σap was observed in the austral autumn and the maximum in the austral spring, similar to other Antarctic sites. The darkest aerosol, i.e., the lowest single-scattering albedo ωo≈0.91, was observed in September and October and the highest ωo≈0.99 in February and March. The uncertainty of the absorption Ångström exponent αap is high. The lowest αap monthly medians were observed in March and the highest in August–October. The equivalent black carbon (eBC) mass concentrations were compared with eBC measured at three other Antarctic sites: the SPO and two coastal sites, Neumayer and Syowa. The maximum monthly median eBC concentrations are almost the same (∼3±1 ng m−3) at all these sites in October–November. This suggests that there is no significant difference in eBC concentrations between the coastal and plateau sites. The seasonal cycle of the eBC mass fraction exhibits a minimum f(eBC) ≈0.1 % in February–March and a maximum ∼4 %–5 % in August–October. Source areas were calculated using 50 d FLEXPART footprints. The highest eBC concentrations and the lowest ωo were associated with air masses coming from South America, Australia and Africa. Vertical simulations that take BC particle removal processes into account show that there would be essentially no BC particles arriving at Dome C from north of latitude 10∘ S at altitudes <1600 m. The main biomass-burning regions Africa, Australia and Brazil are more to the south, and their smoke plumes have been observed at higher altitudes than that, so they can get transported to Antarctica. The seasonal cycle of BC emissions from wildfires and agricultural burning and other fires in South America, Africa and Australia was calculated from data downloaded from the Global Fire Emissions Database (GFED). The maximum total emissions were in August–September, but the peak of monthly average eBC concentrations is observed 2–3 months later in November, not only at Dome C, but also at the SPO and the coastal stations. The air-mass residence-time-weighted BC emissions from South America are approximately an order of magnitude larger than from Africa and Oceania, suggesting that South American BC emissions are the largest contributors to eBC at Dome C. At Dome C the maximum and minimum scattering coefficients were observed in austral summer and winter, respectively. At the SPO σsp was similar to that observed at Dome C in the austral summer, but there was a large difference in winter, suggesting that in winter the SPO is more influenced by sea-spray emissions than Dome C. The seasonal cycles of σsp at Dome C and at the SPO were compared with the seasonal cycles of secondary and primary marine aerosol emissions. The σsp measured at the SPO correlated much better with the sea-spray aerosol emission fluxes in the Southern Ocean than σsp at Dome C. The seasonal cycles of biogenic secondary aerosols were estimated from monthly average phytoplankton biomass concentrations obtained from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) satellite sensor data. The analysis suggests that a large fraction of the biogenic scattering aerosol observed at Dome C has been formed in the polar zone, but it may take a month for the aerosol to be formed, be grown and get transported from the sea level to Dome C.

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Western, Luke M., Alison L. Redington, Alistair J. Manning, Cathy M. Trudinger, Lei Hu, Stephan Henne, Xuekun Fang, Lambert J. M. Kuijpers, Christina Theodoridi, David S. Godwin, Jgor Arduini, Bronwyn Dunse, Andreas Engel, Paul J. Fraser, Christina M. Harth, Paul B. Krummel, Michela Maione, Jens Mühle, Simon O'Doherty, Hyeri Park, Sunyoung Park, Stefan Reimann, Peter K. Salameh, Daniel Say, Roland Schmidt, Tanja Schuck, Carolina Siso, Kieran M. Stanley, Isaac Vimont, Martin K. Vollmer, Dickon Young, Ronald G. Prinn, Ray F. Weiss, Stephen A. Montzka and Matthew Rigby, (2022), A renewed rise in global HCFC-141b emissions between 2017–2021, Atmospheric Chemistry and Physics, 22, 14, 9601-9616, 10.5194/acp-22-9601-2022

Abstract

Abstract. Global emissions of the ozone-depleting gas HCFC-141b (1,1-dichloro-1-fluoroethane, CH3CCl2F) derived from measurements of atmospheric mole fractions increased between 2017 and 2021 despite a fall in reported production and consumption of HCFC-141b for dispersive uses. HCFC-141b is a controlled substance under the Montreal Protocol, and its phase-out is currently underway, after a peak in reported consumption and production in developing (Article 5) countries in 2013. If reported production and consumption are correct, our study suggests that the 2017–2021 rise is due to an increase in emissions from the bank when appliances containing HCFC-141b reach the end of their life, or from production of HCFC-141b not reported for dispersive uses. Regional emissions have been estimated between 2017–2020 for all regions where measurements have sufficient sensitivity to emissions. This includes the regions of northwestern Europe, east Asia, the United States and Australia, where emissions decreased by a total of 2.3 ± 4.6 Gg yr−1, compared to a mean global increase of 3.0 ± 1.2 Gg yr−1 over the same period. Collectively these regions only account for around 30 % of global emissions in 2020. We are not able to pinpoint the source regions or specific activities responsible for the recent global emission rise.