The Effect of Transportation and Wildfires on the Spatiotemporal Heterogeneity of PM_2.5 Mass in the New York-New Jersey Metropolitan Statistical Area

Declining ambient PM_2.5 concentrations have been attributed to fuel consumption standards and emission controls of secondary sulfate and nitrate aerosol precursors from transportation and industrial sectors. As a result, the relative contribution of PM_2.5 sources is modified, shifting PM_2.5 trends, physicochemical characteristics, and health effects. Carbonaceous fine aerosol account for most of PM_2.5 mass in the US. This study aims to examine the spatiotemporal trends of ambient PM_2.5 levels and their association with primary PM_2.5 emissions from anthropogenic activities and fires in the New York/New Jersey metropolitan statistical area (NYNJ MSA) airshed. PM_2.5 mass concentrations were obtained from the U.S. Environmental Protection Agency (USEPA) Air Data. Ambient PM_2.5 mass levels declined on average by 47%, at a rate of -0.61 ± 0.01 μg/m³/year in urban locations and -0.25 ± 0.01 μg/m³/year in upwind and peri-urban locations over the 2007 to 2017 period. The strong spatial gradient in 2007, with high PM_2.5 levels in urban locations and low PM_2.5 levels in peri-urban locations gradually weakened by 2013 but re-appeared in 2017. Over the same period, primary PM_2.5 emissions declined by 52% from transportation, 15% from industrial, and 8% from other anthropogenic sources corresponding to a decrease of 0.8, 0.9, and 0.6 μg/m³ on ambient PM_2.5 mass, respectively. Wildland and prescribed fires emissions increased more than 3 times adding 0.8 μg/m³ to ambient PM_2.5 mass. These results indicate that (i) fire emissions may impede the effectiveness of existing policies to improve air quality and (ii) the chemical content of PM_2.5 may be changing to an evolving mixture of aromatic and oxygenated organic species with differential toxicological responses as compared to inert ammonium sulfate and nitrate salts.