Decadal Trends in the Temperature Dependence of Summertime Urban PM_2.5 in the Northeast United States

Abstract

Temperature has been identified as a key control over particulate matter of diameters smaller than 2.5 μm (PM2.5); however, the mechanisms controlling this phenomenon in urban areas have not been definitively elucidated. With increasing urbanization and associated heat-island effects as well as a warming climate, understanding the role that temperature plays in modulating urban aerosol mass is critical. We explore the link between temperature and aerosol mass using observations from seven cities in the Northeast U.S., finding that summertime PM2.5 exhibits a strong linear dependence on temperature going back at least two decades. Early in this record, the leading cause of the PM2.5 mass increase with temperature was an increase in the ammonium sulfate aerosol mass. We suggest that this was due to increased electricity consumption to support air conditioning on warmer days and the associated SO2 emissions from coal burning power plants. Later in the record and in the present day, the leading cause of the linear correlation of PM2.5 mass with temperature is the increase in organic aerosol mass with temperature. Effective policy for curbing high PM2.5 events in the future will depend on understanding the factors influencing this temperature-dependent enhancement in organic aerosols specifically, whether they are related to biogenic emissions, anthropogenic emissions, or chemical processes.