Remote monitoring towers provide data that advance the understanding of boreal forest fires

June 21, 2021
boreal forest fire
Fire in the boreal forest in Alaska. Photo credit: Scott Rupp | Alaska Climate Adaptation Science Center | June 17, 2009 from https://www.usgs.gov/media/images/fire-boreal-forest-alaska

On June 7, 2021, a new study on carbon monoxide and methane emission from boreal forest fires was published in Atmospheric Chemistry and Physics. Global Monitoring Laboratory scientists Arlyn Andrews, Colm Sweeney, and John Miller were co-authors of the paper and Global Monitoring Laboratory staff provided ongoing remote maintenance of the Carbon in Arctic Reservoirs Vulnerability Experiment (CRV) tower, which provided continuous high-resolution gas observations for this study.

Boreal forest fires influence the global carbon cycle and climate system by consuming aboveground and underground biomass and directly releasing carbon dioxide, other trace gases, and aerosols into the atmosphere. Previous studies have also shown that fire plumes from Alaska and western Canada can influence air quality over Nova Scotia, the south-central United States, and Europe.

This new research quantified emission factors of carbon monoxide and methane using ground-based observations from the CRV tower and identified at least 34 contributing fires in interior Alaska during the summer of 2015. The number of individual wildfires sampled in this study is comparable to the number of individual wildfires sampled in North American in previous studies.

Results suggested that smoldering combustion processes in North American boreal forest fires contribute more trace gas emissions than previous estimates derived from aircraft sampling. The time-series data and derived emission factors may provide a means to test models that integrate together fire processes, emissions, and regional atmospheric transport.

Emission factors convert fire consumption of dry biomass into emissions of specific trace gas species, such as carbon monoxide, methane, and carbon dioxide. Applying these values in fire emission models and comparing the model with observations can help improve the model accuracy and better evaluate how boreal wildfires impact climate and air quality.

Long-term monitoring from remote towers can potentially provide new information about wildfires in other ecosystems, integrating across day-night variations in fire behavior, across periods with different environmental conditions, and across multiple fires in different stages of growth and extinction.

More work is needed to combine tower and aircraft sampling to attain accurate estimates of the total budget of fire-emitted trace gases and aerosols.

The research was supported by the National Science Foundation Graduate Research Fellowship, NASA, and OAR's Climate Program Office. National Environmental Satellite Data and Information Service provided critical labor and infrastructure for the research.

Boreal forest fire CO and CH4 emission factors derived from tower observations in Alaska during the extreme fire season of 2015

Wiggins, E. B., Andrews, A., Sweeney, C., Miller, J. B., Miller, C. E., Veraverbeke, S., Commane, R., Wofsy, S., Henderson, J. M., and Randerson, J. T.: Atmos. Chem. Phys., 21, 8557–8574, https://doi.org/10.5194/acp-21-8557-2021, 2021.

Abstract

Recent increases in boreal forest burned area, which have been linked with climate warming, highlight the need to better understand the composition of wildfire emissions and their atmospheric impacts. Here we quantified emission factors for CO and CH4 from a massive regional fire complex in interior Alaska during the summer of 2015 using continuous high-resolution trace gas observations from the Carbon in Arctic Reservoirs Vulnerability Experiment (CRV) tower in Fox, Alaska. Averaged over the 2015 fire season, the mean CO / CO2 emission ratio was 0.142 ± 0.051, and the mean CO emission factor was 127 ± 40 g kg−1 dry biomass burned. The CO / CO2 emission ratio was about 39 % higher than the mean of previous estimates derived from aircraft sampling of wildfires from boreal North America. The mean CH4 / CO2 emission ratio was 0.010 ± 0.004, and the CH4 emission factor was 5.3 ± 1.8 g kg−1 dry biomass burned, which are consistent with the mean of previous reports. CO and CH4 emission ratios varied in synchrony, with higher CH4 emission factors observed during periods with lower modified combustion efficiency (MCE). By coupling a fire emissions inventory with an atmospheric model, we identified at least 34 individual fires that contributed to trace gas variations measured at the CRV tower, representing a sample size that is nearly the same as the total number of boreal fires measured in all previous field campaigns. The model also indicated that typical mean transit times between trace gas emission within a fire perimeter and tower measurement were 1–3 d, indicating that the time series sampled combustion across day and night burning phases. The high CO emission ratio estimates reported here provide evidence for a prominent role of smoldering combustion and illustrate the importance of continuously sampling fires across time-varying environmental conditions that are representative of a fire season.

For questions or concerns, please contact Xinyi Zeng ( xinyi.zeng@noaa.gov ).