Spatially-explicit characterization of the exposure and health burden of fine particulate matter in the U.S.

Air pollution impacts are estimated using spatialized exposures and dose-response functions. We developed spatially-explicit intake fractions (iF – fraction of the emission taken in by population) and characterization factors (CF – health burden per precursor emission unit) for sector-specific emissions of primary PM2.5, NH3, SO2, and NOx in the U.S. We calculated iFs for 43,304 locations in the contiguous U.S. using a reduced-form chemical transport model, the Intervention Model for Air Pollution (InMAP). For each source location, we integrated iFs multiplied by the non-linear integrated exposure-response function and region-specific burden estimates at each receptor location, both obtained from the Global Burden of Disease, to derive cumulative location-specific CF estimates. Using spatial information of annual emissions for 50 states and 60 sectors, we estimated emissionweighted state and sector-specific iFs and CFs. The emission-weighted national average iF was 0.8 parts per million (ppm) for PM2.5, 0.4 ppm for NH3, 0.3 ppm for SO2, and 0.1 ppm for NOx. Location-specific estimates varied up to three orders of magnitude, driven by population. Using an average exposure-response slope between background and “no risk” PM2.5 levels, national CFs were estimated at 209, 99, 75, and 38 μDALYs/kg for PM2.5, NH3, SO2, and NOx, respectively. State CFs varied substantially with a precursor-dependent range. For PM2.5, CFs
varied by a factor 60 from highest (Arizona) to lowest state (North Dakota). For NH3 CFs varied by factor of 40 by state and for NOx and SO2 by a factor of 10. A marginal slope resulted in twice-lower estimates. For PM2.5 and NH3, CFs for the mobile sector were ~5 times higher than those for the agriculture sector. We found little variability between sectors for SO2 and NOx emissions. Results highlight the importance of spatial and sectorspecific estimates in characterizing more accurately the health burden of PM2.5.