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Wildfire influences on the variability and trend of summer surface ozone in the mountainous western United States

Xiao Lu, Lin Zhang, Xu Yue, Jiachen Zhang, Daniel A. Jaffe, Andreas Stohl, Yuanhong Zhao, Jingyuan Shao
2016 Atmospheric Chemistry and Physics  
<p><strong>Abstract.</strong> Increasing wildfire activities in the mountainous western US may present a challenge for the region to attain a recently revised ozone air quality standard in summer. Using current Eulerian chemical transport models to examine the wildfire ozone influences is difficult due to uncertainties in fire emissions, inadequate model chemistry, and resolution. Here we quantify the wildfire influence on the ozone variability, trends, and number of high MDA8 (daily maximum
more » ... 8 (daily maximum 8<span class="thinspace"></span>h average) ozone days over this region in summers (June, July, and August) 1989–2010 using a new approach. We define a fire index using retroplumes (plumes of back-trajectory particles) computed by a Lagrangian dispersion model (FLEXPART) and develop statistical models based on the fire index and meteorological parameters to interpret MDA8 ozone concentrations measured at 13 Intermountain West surface sites. We show that the statistical models are able to capture the ozone enhancements by wildfires and give results with some features different from the GEOS-Chem Eulerian chemical transport model. Wildfires enhance the Intermountain West regional summer mean MDA8 ozone by 0.3–1.5<span class="thinspace"></span>ppbv (daily episodic enhancements reach 10–20<span class="thinspace"></span>ppbv at individual sites) with large interannual variability, which are strongly correlated with the total MDA8 ozone. We find large fire impacts on the number of exceedance days; for the 13 CASTNet sites, 31<span class="thinspace"></span>% of the summer days with MDA8 ozone exceeding 70<span class="thinspace"></span>ppbv would not occur in the absence of wildfires.</p>
doi:10.5194/acp-16-14687-2016 fatcat:xxhhpiqncvgqdnwy7nj2bqky6m