Evaluation of Aerosol Optical Depth (AOD) and PM2.5 associations for air quality assessment

Traditional station-based PM2.5 monitoring method has significant spatial gaps. Moderate Resolution Imaging Spectrometer (MODIS) Aerosol Optical Depth (AOD) product (10 km spatial resolution) derived from the imagery of NASA Terra satellite has been used as a tool for regional PM2.5 studies for many years. Literature suggested mixed results on AOD-PM2.5 correlation across geographic location, size of study area, and spatial resolution of MODIS AOD product. Also, correlation coefficient was reported at seasonal or yearly level and seldom any atmospheric research reported the AOD-PM2.5 correlation at daily level, which is crucial to utilize MODIS AOD products in air quality assessment. In this study, MODIS AOD product with 1, 3, and 10 km spatial resolutions were employed to examine their linear relationship with hourly PM2.5 data at daily level in order to evaluate their feasibility for PM2.5 remote monitoring in the state of North Carolina, U.S. First, the daily correlation between MODIS AOD value and ground PM2.5 concentration was statistically analyzed for the day in which both data existed. Next, a site-specific AOD-PM2.5 correlation was examined for each AirNow PM2.5 station in NC at 1 km, 3 km and 10 km spatial resolutions respectively in 2011 and 2012. The significance of all correlations was tested at 95% confidence level for each day at which two pairs of PM2.5 and AOD existed and each station in both years. It was found that the site-specific correlation between MODIS AOD value and ground PM2.5 concentration was statistically significant (95% confidence level) at majority of PM2.5 monitoring stations at 1 km, 3 km and 10 km level in both 2011 and 2012 in NC. Our results suggest that it is practicable to use MODIS AOD data to assess PM2.5 concentrations monthly at both city and state level without incorporating meteorological parameters.Main finding: Significant site-specific AOD-PM2.5 correlations allow the application of MODIS AOD to air quality assessment;