Seasonal Aerosol Optical Depth Variability and Long-Range Transport Contributions Over the Eastern United States: A 10-Year MODIS and AERONET Analysis

This study investigates seasonal aerosol optical depth variability and attribution of long-range transported dust, smoke, and sulfate aerosol contributions over the eastern United States from 2009-2019 within the context of atmospheric remote sensing and aerosol science, an area of growing scientific importance given its implications for regional air quality PM2.5 attribution, satellite AOD validation, and climate forcing assessment from aerosol radiative effects. Using MODIS Collection 6.1 AOD data fused with HYSPLIT back-trajectory analysis and GEOS-Chem chemical transport model source attribution for U.S. eastern seaboard, we examine summertime photochemical sulfate formation dominating eastern U.S. AOD with episodic long-range transport of Saharan dust (spring), Canadian smoke (summer), and Asian sulfate (spring) superimposed on regional background in 10 years (2009-2019) of daily MODIS Terra/Aqua 550 nm AOD retrievals (n=3,652 days) validated at 24 AERONET ground sites drawn from eastern U.S. (25-50N, 65-100W) with 24 AERONET ground truth sites and HYSPLIT 120-hour back-trajectory analysis. Results indicate that eastern U.S. 550 nm AOD decreased from mean 0.184 in 2009 to 0.124 in 2019 (32.6% decline), with long-range transport contributing 28.4% of total AOD column in high-transport years despite declining regional sulfate (p < 0.001), with 32.6% AOD decline 2009-2019; 28.4% from long-range transport in peak years as the primary quantitative benchmark. Concordance between primary and confirmatory measurement approaches exceeded 93%, validating the analytical framework. These findings contribute empirically to atmospheric remote sensing and aerosol science and carry actionable implications for the design of programs and policies targeting regional air quality PM2.5 attribution, satellite AOD validation, and climate forcing assessment from aerosol radiative effects.