Fires in the Western US: Analyzing Emitted Speciated Organic Trace Gases and Aerosols and their Atmospheric Chemical Transformations

Wildfires, particularly in the forested regions of the western U.S., are becoming larger and increasingly more frequent. Understanding local and regional effects on air quality is needed to inform fire management practices and to ensure the health and safety of humans in affected regions. Understanding the global contributions of these wildfires is important to assessing effects on climate. Biomass burning (BB) is the main global source of primary carbonaceous aerosol and the second largest global source of non-methane organic compounds, including volatile and semi-volatile organic compounds that are now understood to be a major contributor to secondary particle formation in the atmosphere. Measured changes in physical properties and chemical composition suggest substantial and rapid chemical aging of BB organic aerosol. While research into the specific trace gases emitted using comprehensive techniques has begun, much work remains especially in the area of characterizing the chemical composition of the semi-volatile and particulate phase of BB organic emissions and their secondary products.

The proposed research aims to elucidate the speciated chemical composition and transformations of intermediate to low-volatility organic compounds emitted from BB. The FIREX study is being planned with a major focus on closing the gap in knowledge by providing unprecedented emission profiling coupled with plume tracking measurements and modeling to predict BBOA levels. Once these air masses are photochemically aged for hours to days, detailed chemical analyses including a full suite of organic aerosol source and product markers are needed to understand mass closure between modeled and measured organic aerosol.

Through powerful chemical separation and identification techniques and by obtaining unprecedented hourly time resolution for chemically speciated measurements of oxygenated intermediate and semi-volatile organic compounds and particle phase organic compounds during FIREX, we expect to make substantial progress in understanding the formation and transformation of wildfire impacts on aerosol loadings in the atmosphere. In-situ hourly gas chromatography mass spectrometry measurements of molecular markers will be made to chemically characterize BB influence and capture diurnal, meteorological and chemical variability. Filter and adsorbent cartridge samples we collect as part of this campaign will be chemically speciated with novel techniques in the laboratory, enabling the discovery of new molecular level markers from both primary and secondary BB sources. Furthermore, through close collaboration with other members of the FIREX Team, our measurements will be used by multiple research groups to address FIREX science questions.