RII Track-4 Biomass Burning Aerosols in the U.S. Southwest: Hygroscopic Properties from Emissions to Aging

New Mexico Institute Of Mining And Technology, Socorro NM

Investigators

Abstract

Nontechnical Description Wildland fire is an increasing global issue and particularly urgent in the western U.S. Due in part to continued increasing temperatures and drought in the nation, the average U.S. acreage burned in wildfires has increased by approximately a factor of 2 since the year 2000 in comparison with the time range of 1960-2000. Beyond tragic loss of life and property associated with extreme events of the past two decades, wildfire trends also prompt growing concerns with health impacts from biomass smoke. Notably, the high concentration of particulate matter, also known as aerosols is of particular concern for human health effects, atmospheric visibility impacts, and the planetary radiation budget. Smoke aerosols are highly diverse in terms of their size, chemical composition, shape and optical properties. This research examines these properties in laboratory combustion experiments using relevant fuels as well as ambient measurements of smoke aerosols. A particular focus is how these particles interact with atmospheric relative humidity, which changes these optical properties. In the end, parameters measured here are important to understanding the magnitude and extent of smoke impacts; these are also key inputs needed in computer models that predict smoke impacts on air quality and the climate system. The study under this fellowship will allow unparalleled opportunities for the career advancement of the PI and a student. Technical Description Biomass burning aerosols increasingly degrade global air quality and remain poorly constrained with respect to climate effects. The Southwestern U.S. lacks detailed measurements of fundamental smoke properties for relevant fuels, for both endemic and invasive species. This project addresses these gaps with laboratory experiments on biomass burning emissions with a focus on aerosol water uptake, or hygroscopicity. The research focuses on laboratory aerosol measurements of biomass smoke?from emission to aging exploring the dynamics between aerosol hygroscopicity, optical properties, and chemical composition. Specific goals of this research are: (1) Explore the connection of aerosol hygroscopicity to fuels and soils, (2) Refine a new technique for measuring humidity dependence of aerosol light extinction using the Cavity Attenuated Phase Shift-Single Scattering Albedo (CAPS-SSA) method, (3) Use other advanced aerosol measurement techniques to describe a framework that drives smoke aerosol properties. An array of techniques will be employed to provide unique insights to biomass smoke microphysical properties. These include several contributed by New Mexico Tech (controlled RH nephelometry, multi-wavelength nephelometry, and a photoacoustic extinctiometer) that will be combined with resources at Los Alamos National Lab (LANL). The latter includes photoacoustic spectrometry, particle size distribution methods, and advanced aerosol techniques such as aerosol mass spectrometry and a photochemical aging reactor. A main collaborative task is the development of a new instrument, a humidified CAPS-SSA. In conjunction with traditional humidity controlled nephelometry, this will allow probing of the RH dependence of light absorption and SSA. The latter determines whether aerosols cause a net cooling or warming impact. This study also includes analysis of plants and soils to determine key drivers of hygroscopicity. Ultimately, the results enable development of a predictive framework of key aerosol properties from smoke, fuel, and soils composition, combustion properties and aging. Wildfire trends as well as the Southwest U.S. region's changing forest ecosystems, a hydrological connection, and scarce data in this region make this an important topic. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.