Abstract View
Reconciling Assumptions in Bottom Up and Top Down Approaches for Estimating Aerosol Emissions from Wildland Fires in the Western US Using Observations from FIREX-AQ
ELIZABETH WIGGINS, Bruce Anderson, Matthew Brown, Gao Chen, Ewan Crosbie, Josh DiGangi, Glenn Diskin, Marta Fenn, Michael Shook, Amber Soja, Francesca Gallo, Emily Gargulinski, Hongyu Guo, Johnathan Hair, Demetrios Pagonis, Anne Perring, Claire Robinson, Kevin Sanchez, Melinda Schueneman, Chelsea Stockwell, Kenneth Thornhill, Carsten Warneke, Joshua P. Schwarz, Taylor Shingler, et al., NASA
Abstract Number: 492
Working Group: Wildfire Aerosols
Abstract
Wildland fires in the Western United States emit a substantial quantity of trace gas and particulate matter that can severely degrade local to regional air quality and ultimately influence climate. However, it is difficult to accurately quantify biomass burning emissions due to the highly variable composition of the fuels they consume and their dynamic behavior. There are two traditional methods to calculate fire emissions, the “bottom up” approach and the “top down” approach. The bottom up approach aims to calculate the mass of fuel consumed by the fire on the ground to quantify emissions, while the top down approach uses fire radiative power (FRP) observed from remote sensing as a proxy for the mass of fuel consumed. The fraction of the total mass emitted in the form of particulate matter (PM) can then be determined via the use of an emission factor for the bottom up approach or through aerosol optical depth observations for the top down approach. The two approaches often disagree by an order of magnitude or more on the mass of PM emitted by fires, but validation is challenging, and it remains difficult to determine which approach is correct.
In situ and remote sensing airborne measurements from the recent NASA/NOAA campaign Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) provide the opportunity to evaluate the two traditional approaches to calculate emissions. In this study, we calculate fire PM emission rates from Western US wildland fires sampled during FIREX-AQ using an independent approach that relies on the integration of smoke plume observations and information gleaned from airborne LIDAR measurements from HSRL. We also calculate fire PM emission rates using the traditional bottom up and top down style approaches. We compare our PM emission rate estimates from the in situ based approach with the traditional approaches to investigate potential bias. We find the bottom up approach has the best agreement with the in situ approach, but with a high level of noise. The top down approach systematically overpredicts fire emissions on the lower end of the range compared to the in situ approach, but the data is much more tightly clustered. The results of our analysis improve our understanding of how to correctly quantify fire aerosol emissions, and have larger implications for using aerosol optical depth remote sensing observations to estimate the mass of PM emitted by fires.