Back trajectory analysis: air parcel histories and forest pollutant exposure

Abstract

Population, land cover, and regional pollutant emissions were analyzed for each of the five flow regimes indentified at UMBS in order to assess the pollutant levels for arriving air masses. The results show that the south/southwest and east/southeast flow regimes display the highest levels of NOx, CO, and anthropogenic VOC exposure (in terms of kilograms/square kilometer/ozone season day(OSD)) while the north/northwest and northeast flow regimes display the lowest. NOx, CO, and anthropogenic VOC exposure levels were estimated to be 18.0, 82.0, and 14.0 kg/km2/OSD, respectively, for the south/southwest flow regime; 10.2, 57.4, and 9.3 kg/ km2/OSD, respectively, for the east/southeast flow regime; 6.9, 29.5, and 5.0 kg/ km2/OSD, respectively, for the west flow regime; 0.8, 3.8, and 0.5 kg/km2/OSD, respectively, for the northeast flow regime; and 0.4, 1.8, and 0.3 kg/ km2/OSD, respectively, for the north/northwest flow regime. Pollution exposure levels were estimated for back trajectories according to the anthropogenic emissions (known point and area sources) for each flow regime as a whole. This method of assessing pollutant exposure was then compared with a finer-scale treatment that follows an individual trajectory. The comparison showed the coarse-scale treatment can result in both underestimates and overestimates of pollutant exposure depending on the trajectory’s path.