Characterizing the origins of atmospheric particulate matter

When developing policy targeted at decreasing air pollution, it is essential that we have a strong understanding of when and where the pollution originated. Towards this goal, we have implemented and evaluated two different source attribution schemes in PMCAMx, a three-dimensional atmospheric chemical transport model. The two schemes, an online (OPSA) and offline version (PSAT), are both designed for computational efficiency and the ability to track source contributions to primary and secondary particulate matter. The two versions showed good agreement with each other and with more accurate, computationally demanding methods. The off-line algorithm (Particulate Source Apportionment Technology, PSAT) is simpler to implement, has a lower computational cost and is suitable for a range of source apportionment studies.;We have utilized this algorithm to study the age distribution of atmospheric particulate matter mass in space and time. The average calculated ages are on the order of a few days for particulate matter near the ground, but are highly variable in space and time. Primary aerosol species had average ages of approximately 24 hours over this polluted continental region while the average ages for secondary species were 48-72 hours near the surface. As expected, the average age of all aerosol components increases vertically in the atmosphere. Age increases rapidly away from the sources of aerosol and its precursors and for non-volatile species it increases with particle size.;PSAT is an excellent tool for the study of source-receptor relationships. We have studied the extent of pollutant transport in the Eastern United States using two approaches. The first PSAT-based approach is focused on source regions and the second is focused on receptor regions. For the source region focused approach, transport of pollutants is quantified by tracking the emissions from these regions. For the receptor region focused approach, PSAT tracks the pollutants emitted from a series of rings around the area of interest We discuss the results from these approaches looking at the impacts to primary elemental carbon, SO2, particulate sulfate and secondary organic aerosol.;The source region-focused approach was applied to study the contributions to PM levels of 11 different area in the Eastern United States, ranging in size (both in terms of land area and emissions) from the Ohio River Valley to Little Rock, AR. These impacts were quantified using a variety of measures to account for both the distance that the pollutants are transported and the overall impact the emissions have on pollutant concentrations in the region. Large source regions were found to have a large impact on secondary particulate matter levels areas several hundred kilometers from the source region.;The receptor region focused approach was used to evaluate the contributions from long range, mid range and long range transport to particulate matter concentrations in three receptor regions: Pittsburgh, PA, Atlanta, GA and Great Smoky Mountains. The local impacts to elemental carbon in urban areas were found to be substantial (approximately 50%) with most the additional contributions being from short range transport. The contributions to sulfate and SOA were found to be more regional with much of the contributions in all three sites resulting from mid range transport.