Downwind particulate matters: Regulatory implications of secondary aerosol formation from the interaction of nitrogen oxides and tree emissions

• Downwind NOx SOA could contribute significantly to power plant PM2.5 emissions.
• Regionally differing tree emissions create variability in the drivers of downwind PM2.5.
• Current federal and state regulations likely underestimate power plant PM2.5 emissions.
• Future regulation of power plants should consider interactions of NOx with local flora.

Current federal and state regulations do not consider proximity and variability of biogenic volatile organic compound emissions, which produce additional particulate matter (PM) emissions from currently operating power plants. This paper estimates that secondary organic aerosol (SOA) production potential from 284 power plants that represent the top NOx emission point sources in the continental United States. This additional source of PM arises from the nitrate radical oxidation of monoterpenes emitted from surrounding trees. For the majority of these point sources, this SOA production is monoterpene-limited, but for an increasing fraction over time (3.5% in 2008 to 12% in 2011) it is NOx-limited. Therefore emissions regulation has the capacity to control this source of PM, which for some sites is estimated to contribute a particle concentration of similar magnitude to the conventionally tracked sulfate particulate emission. This analysis, while highly approximate, points to the opportunity for more nuanced PM2.5 regulation to more effectively manage power plant air quality impact.

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