Variability and potential sources of summer PM2.5 in the Northeastern United States

Abstract

The variability of ground-level concentrations of fine suspended particulate matter (PM2.5) in the Northeastern United States is examined using observed PM2.5 from multiple data networks together with output from the Modern-Era Retrospective Analysis for Research and Applications Aerosol Reanalysis (MERRAero). The long-term variations as well as the occurrence of short-term high-concentration episodes in the region are investigated for the period 1999–2013. This analysis shows that over this period there has been a significant decrease in summer-mean PM2.5. A decrease in the occurrence and magnitude of high-PM2.5 events in the Northeastern U.S. region is also observed. The potential sources of PM2.5 are analyzed using MERRAero aerosol optical depth for two of the main components of the pollutant: organic carbon and ammonium sulfate. The analysis indicates that high-PM2.5 events in the Northeastern U.S. are, generally, the result of long range transport of smoke from large boreal wildfires, Midwestern industrial emissions, or a combination of both. There are roughly equal numbers of events due to natural or anthropogenic sources for the 2002–2012 period for this region. The events that have an anthropogenic source are characterized by a strong high pressure system in the Southern U.S. that cause aerosols to be advected from the Midwest into the Northeastern U.S. The meteorology related to wildfire events is more variable, consistent with the varied locations of the fires that cause aerosol events in the Northeastern U.S.