A Bulk-Mass-Modeling-Based Method for Retrieving Particulate Matter Pollution Using CALIOP Observations
Journal Article - Open Access
NAVAL RESEARCH LAB WASHINGTON DC WASHINGTON United States
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In this proof-of-concept paper, we apply a bulk-mass-modeling method using observations from the NASA Cloud-Aerosol Lidar with Orthogonal Polarization CALIOP instrument for retrieving particulate matter PM concentration over the contiguous United States CONUS over a 2-year period 2008-2009. Different from previous approaches that rely on empirical relationships between aerosol optical depth AOD and PM2.5 PM with particle diameters less than 2.5 mu m, for the first time, we derive PM2.5 concentrations, during both daytime and nighttime, from near-surface CALIOP aerosol extinction retrievals using bulk mass extinction coefficients and model-based hygroscopicity. Preliminary results from this 2-year study conducted over the CONUS show a good agreement r2 similar to 0.48 mean bias of -3.3 mu gm-3 between the averaged nighttime CALIOP-derived PM2.5 and ground-based PM2.5 with a lower r2 of similar to 0.21 for daytime mean bias of -0.4 mu gm-3, suggesting that PM concentrations can be obtained from active-based spaceborne observations with reasonable accuracy. Results from sensitivity studies suggest that accurate aerosol typing is needed for applying CALIOP measurements for PM2.5 studies. Lastly, the e-folding correlation length for surface PM2.5 is found to be around 600 km for the entire CONUS similar to 300 km for western CONUS and similar to 700 km for eastern CONUS, indicating that CALIOP observations, although sparse in spatial coverage, may still be applicable for PM2.5 studies.