Abstract
Abstract. Significant reductions in emissions of SO2, NOx, volatile organic compounds (VOCs), and primary particulate matter (PM) took place in the US from 1990 to 2010. We evaluate here our understanding of the links between these emissions changes and corresponding changes in concentrations and health outcomes using a chemical transport model, the Particulate Matter Comprehensive Air Quality Model with Extensions (PMCAMx), for 1990, 2001, and 2010. The use of the Particle Source Apportionment Algorithm (PSAT) allows us to link the concentration reductions to the sources of the corresponding primary and secondary PM. The reductions in SO2 emissions (64 %, mainly from electric-generating units) during these 20 years have dominated the reductions in PM2.5, leading to a 45 % reduction in sulfate levels. The predicted sulfate reductions are in excellent agreement with the available measurements. Also, the reductions in elemental carbon (EC) emissions (mainly from transportation) have led to a 30 % reduction in EC concentrations. The most important source of organic aerosol (OA) through the years according to PMCAMx is biomass burning, followed by biogenic secondary organic aerosol (SOA). OA from on-road transport has been reduced by more than a factor of 3. On the other hand, changes in biomass burning OA and biogenic SOA have been modest. In 1990, about half of the US population was exposed to annual average PM2.5 concentrations above 20 µg m−3, but by 2010 this fraction had dropped to practically zero. The predicted changes in concentrations are evaluated against the observed changes for 1990, 2001, and 2010 in order to understand whether the model represents reasonably well the corresponding processes caused by the changes in emissions.
Highlights
During recent decades, regulations by the US Environmental Protection Agency (EPA) have led to significant reductions in the emissions of SO2, NOx, volatile organic compounds (VOCs), and primary particulate matter (PM) from electrical utilities, industry, transportation, and other sources (US EPA, 2011). Xing et al (2013) estimated that, from 1990 to 2010, emissions of SO2 in the US were reduced by 67 %, NOx by %, non-methane VOCs by %, and primary PM2.5 by 34 %
We examine first the source apportionment results of PMCAMx-Particle Source Apportionment Algorithm (PSAT) for the major components of PM2.5 for the 3 simulated years
On-road transportation was a major source of elemental carbon (EC), especially in urban areas in 1990 (Fig. 2)
Summary
Regulations by the US Environmental Protection Agency (EPA) have led to significant reductions in the emissions of SO2, NOx, VOCs, and primary PM from electrical utilities, industry, transportation, and other sources (US EPA, 2011). Xing et al (2013) estimated that, from 1990 to 2010, emissions of SO2 in the US were reduced by 67 %, NOx by %, non-methane VOCs by %, and primary PM2.5 by 34 %. There have been several efforts to quantify historical changes in PM2.5 levels and composition These rely heavily on measurements (both ground and satellite for the more recent changes) and on a number of statistical techniques including land-use regression models to calculate the concentrations of PM2.5 over specific areas and periods (Eeftens et al, 2012; Beckerman et al, 2013; Ma et al, 2016; Li et al, 2017a). Li et al (2017b) combined in situ and satellite observations with the global CTM, GEOS-Chem, to quantify global and regional trends in the chemical composition of PM2.5 over 1989–2013 They concluded that the predicted average trends for North America were consistent with the available measurements for PM2.5, secondary inorganic aerosols, organic aerosols, and black carbon. We quantify trends in population exposure and estimated health outcomes
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