Investigating Aerosol Optical Properties from Long-Range Transport Smoke to The Southern Great Plains U.S.

Abstract

With an increasing number and intensity of wildfires each year, exposure to smoke is a growing health concern. These fires produce large loadings of aerosols, which have intense local effects and also travel thousands of miles downwind. While many field campaigns have been developed to study smoke's physical and chemical properties near the smoke plumes within the U.S., the effects on aerosol physical properties due to long-range transport aging have been less examined. This is especially important as travel times’ effects on aerosol properties are not represented in many atmospheric models. This investigation aims to improve the understanding of aerosol physical properties such as aerosol optical depth (AOD), extinction Ångström exponent (EAE), single scattering albedo (SSA), and absorption Ångström exponent (AAE) in the Southern Great Plains (SGP), specifically Oklahoma. A total of twenty-seven cloud-free smoke events between 2015 and 2022 were identified using a combination of MODIS Deep Blue (DB) AOD maps, AERONET ground station data, and HYSPLIT back-trajectories parameterized by MicroPulse Lidar (MPL) determined plume height. Results indicate that an elevated AOD (~0.2 to ~0.3) path between the western U.S. and the SGP with peaks of AOD > 0.4 in August and September. Comparisons of AERONET observations across various sites revealed evidence of long-range transport, with AOD, EAE, and SSA decreasing and AAE increasing as the smoke traveled to Billings, OK. Mean AOD decreased by ~0.21, ~0.38, ~1.69, ~1.42, and ~0.1, while mean EAE decreased by ~0.13, ~0.2, ~0.25, ~0.18, and ~0.2 for zero through four-day travel time, respectively. Mean SSA decreased by ~0.02, ~0.02, <0.01, ~0.02, and ~0.01, while mean AAE increased by ~1.26, ~0.16, ~0.04, ~0.34, and ~0.32, respective to travel time. While lower arrival height may be associated with shorter travel times, the underlying meteorology (troughs and ridges) driving wind direction and intensity seem to be the primary determinant of the plume path. The study's findings highlight the need for further research to explore the impact of meteorological conditions and variations in fuel type on smoke aerosol optical properties, with an emphasis on using remote sensing methods for broader analysis.