GML Seminars

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Seminars for 2009

Title:

Atmospheric Chemistry over the Oceans
Speaker: Eric Hintsa
NSF, Arlington, VA
Date/Time: Tuesday, February 10, 2009 03:30 PM MST (-0700)
Location: NOAA David Skaggs Research Center, Room 3D512 – GMD third floor conference room
Abstract
The composition of the marine atmosphere is influenced by fluxes to and from the oceans, transport, and chemical and physical processing. I will describe work in two areas that addresses these issues: measurements of atmospheric composition from ocean buoys and towers, and determination of the flux of dimethylsulfide (DMS) and other gases from the ocean. At the Woods Hole Oceanographic Institution, I developed, built and deployed ozone instruments combined with a simple meteorological package for long-term operation at sea. Deployment locations included the Chesapeake Light Tower and a buoy in the Gulf of Maine during ICARTT. Results from these studies will be presented focusing on ozone chemistry and transport over coastal areas. In order to improve our understanding of the marine sulfur cycle and the physical processes that govern air-sea gas exchange, DMS fluxes were measured by three techniques from ships and coastal sites. We implemented the Gradient Flux (GF) method and compared it with Relaxed Eddy Accumulation (REA) and Eddy Covariance (EC). In GF, samples are obtained simultaneously at different elevations and subsequently analyzed by gas chromatography. Reasonably good agreement was obtained between the GF and REA techniques.
Title:

Biogenic Matter Influences on SO2 Oxidation and Removal from the Marine Boundary Layer and its Role in Over Ocean CCN Aerosol Characterization
Speaker: Herman Sievering
U.of Colorado, Boulder, CO
Date/Time: Tuesday, May 5, 2009 10:00 AM MDT (-0600)
Location: NOAA David Skaggs Research Center, Room 2A305
Abstract

Marine boundary layer (MBL) aerosol measurements have shown that O3-oxidation of SO2 in seasalt aerosols plays an important role in global MBL sulfur cycling and budgets. Field studies at Baring Head, NZ and, recently, at Cape Grim, AU show that biogenic matter from upwind surface waters' primary productivity (PP) not only provides alkalinity to "feed" this seasalt O3-oxidation of SO2 but also produces submicron biogenic-derived aerosols that are active CCN. At Baring Head, substantial upwind PP provided enough alkalinity for O3-oxidation to remove all DMS-derived SO2 back to ocean surface waters. Model estimates of effective SO2 dry deposition velocities (effVd), once accounting for removal in seasalt aerosols, show effVd is 3- to 10-times that of direct SO2 gaseous dry deposition velocities. These large effVd indicate that DMS-derived, submicron non-seasalt sulfate aerosols contribute far less to cloud condensation nuclei (CCN) in the MBL than previously thought.

Cape Grim aerosol sampling took place at 110 m asl (completely removed from local soil and seaspray aerosols) with upwind ocean surface waters' PP at global ocean mean PP levels. Ratios of submicron aerosol excess K+ to excess Ca++ (beyond bulk seawater K+ and Ca++) indicate that 50-500 nm aerosols have very different characteristics when upwind PP is or is not active. During periods of much reduced upwind PP (e.g., winter), fragmented plankton debris dominates the surface waters biogenic matter contribution to these CCN size aerosols. During PP active periods, our ion data suggest several biogenic matter sources produce 50-500 nm aerosols. Electron microscope analysis of Cape Grim aerosols show the large majority of 10-100 nm aerosols to be a mix of fragmented marine organisms coated with highly surface active polymer gels, or gels themselves; thus active CCN. Very few <100 nm seasalt or ammonium sulfate aerosols were found. The biogenic matter aerosol source has important consequences for the concentration and character of CCN in the MBL.

Co-authors: J. Cainey (Cape Grim Baseline Stn., AU), M. Harvey (NIWA, NZ), M. Keywood (CSIRO, AU), C. Leck (Stockholm U.) and R. von Glasow (U. of East Anglia, UK)

Title:

Increase in Background Stratospheric Aerosol Since 2000: Is it Related to Increased Coal Burning in China?
Speaker: Dave Hofmann
CIRES, ESRL/GMD
Date/Time: Tuesday, May 19, 2009 03:30 PM MDT (-0600)
Location: Multi-purpose Room (GC-402) David Skaggs Research Center (DSRC)
Abstract
The stratospheric aerosol layer has been monitored with lidars at Mauna Loa Observatory in Hawaii and Boulder in Colorado since 1975 and 2000, respectively. Following the decay of aerosol related to the Pinatubo volcanic eruption in June 1991, the global stratosphere has not been perturbed by a major volcanic eruption and has provided an excellent opportunity to study the background aerosol free of major volcanic perturbations. Since about 2000, an increase of 4-8 % per year in the aerosol backscatter in the altitude range 20-30 km has been detected at both Mauna Loa and Boulder. This increase is superimposed on a winter seasonal maximum which is modulated by the quasi-biennial oscillation (QBO) in tropical winds. Of the three major causes for a stratospheric aerosol increase: volcanic emissions to the stratosphere, increased tropical upwelling, and an increase in anthropogenic sulfur gas emissions in the troposphere, it appears that a large increase in coal burning since 2002, mainly in China, is the likely source of sulfur dioxide which ultimately ends up as the sulfate aerosol responsible for the increased backscatter from the stratospheric aerosol layer.
Title:

Increase in Background Stratospheric Aerosol Since 2000: Is it Related to Increased Coal Burning in China?
Speaker: David Hoffman
NOAA/ESRL and CU/CIRES
Date/Time: Tuesday, June 9, 2009 10:00 AM MDT (-0600)
Location: David Skaggs Research Center, Room GC402
Abstract
The stratospheric aerosol layer has been monitored with lidars at Mauna Loa Observatory in Hawaii and Boulder in Colorado since 1975 and 2000, respectively. Following the decay of aerosol related to the Pinatubo volcanic eruption in June 1991, the global stratosphere has not been perturbed by a major volcanic eruption and has provided an excellent opportunity to study the background aerosol free of major volcanic perturbations. Since about 2000, an increase of 4-8 % per year in the aerosol backscatter in the altitude range 20-30 km has been detected at both Mauna Loa and Boulder. This increase is superimposed on a winter seasonal maximum which is modulated by the quasi-biennial oscillation (QBO) in tropical winds. Of the three major causes for a stratospheric aerosol increase: volcanic emissions to the stratosphere, increased tropical upwelling, and an increase in anthropogenic sulfur gas emissions in the troposphere, it appears that a large increase in coal burning since 2002, mainly in China, is the likely source of sulfur dioxide which ultimately ends up as the sulfate aerosol responsible for the increased backscatter from the stratospheric aerosol layer.
Title:

Sulfate aerosol effects on climate: The observational pathway to the first estimates of forcing

Speaker: Robert J. Charlson
Professor, Department of Atmospheric Sciences and Department of Chemistry, University of Washington, Seattle, WA
Date/Time: Thursday, June 18, 2009 03:30 PM MDT (-0600)
Location: Multi-purpose Room (GC-402), David Skaggs Research Center (DSRC), NOAA Building, DOC Boulder Campus
Abstract
In the 1960's, development of the integrating nephelometer for atmospheric aerosols made possible the measurement of relationships between mass concentration and the scattering component of optical extinction at visible wavelengths. While the initial application of this device was atmospheric visual range, application to the issue of aerosol effects was undertaken in the 1970's, with the first paper by Bolin and Charlson suggesting a dominant role for anthropogenic sulfates from the atmospheric oxidation of sulfur dioxide. Even though the data needed for a global climate forcing calculation were all available by 1976, the first quantitative global estimates did not result until 1988 (with a model) and 1990 (with observational data). This talk traces the development and many applications of the integrating nephelometer to the point of observationally quantifying the effect of sulfates on light scattering, the wavelength and angular scattering characteristics of the scattered light and the dependence of scattering coefficient on relative humidity. Subsequent melding of the optical data with a simple chemical box model of the atmospheric sulfur cycle then provided the necessary means to scale upward from local measurements to large scale effects. Conclusions will include identifying the needed observational links for connecting the in-situ observational optical and chemical data to the global observations made with satellite-based instruments.
Title:

Why Hasn't Earth Warmed as Much as Expected?
Speaker: Stephen E. Schwartz
Brookhaven National Laboratory, Upton NY
Date/Time: Friday, October 2, 2009 02:00 PM MDT (-0600)
Location: David Skaggs Research Center, Room GC402
Abstract
The observed increase in global mean surface temperature (GMST) over the industrial era, about 0.8 K, is less than 40% of that expected from observed increases in long-lived greenhouse gases together with the best-estimate equilibrium climate sensitivity given by the 2007 Assessment Report of the Intergovernmental Panel on Climate Change. This warming discrepancy is due mainly to some combination of two factors: too high a climate sensitivity and/or partial offset of the greenhouse gas forcing by increased concentrations of atmospheric aerosols; thermal disequilibrium accounts for less than 25% of the discrepancy, and cooling by natural temperature variation might account for 15%. Current uncertainty in climate sensitivity precludes determining the amount of future fossil fuel CO2 emissions that would be compatible with any chosen maximum allowable increase in GMST; even the sign of such allowable future emissions is unconstrained. Resolving this situation requires substantial reduction in the uncertainty of aerosol forcing.

Speaker's home page is http://www.ecd.bnl.gov/steve

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