How air pollution changes with weather conditions in beiging
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ExplanHourly O3 and daily 24 h PM2.5 concentrations were obtained from the US Environmental Protection Agency (EPA)'s Air Quality System and Speciation Trend Networks, and Interagency Monitoring of Protected Visual Environments network. We selected sites with at least 10 years of year-round (January–December) data in 1994–2012 and at least 14 daily measurements each month; this yielded 468 O3 sites and 62 PM2.5 sites (figure 2). We chose 1994 as the starting year due to wider availability of O3 measurements. Of note, most PM2.5 measurements are available starting 1998. As we ultimately assess health impacts, sites were categorized into seven regions (Industrial Midwest (IM), Northeast (NE), Northwest (NW), Southeast (SE), Southern California (SC), Southwest (SW), Upper Midwest (UM)) as defined by the National Morbidity Mortality Air Pollution Study (NMMAPS) (Samet et al 2000). As the national O3 standards are based on the annual 4th highest maximum daily 8 h average averaged over 3 years, we computed the daily 8 h max O3 metric utilizing a 75% data capture criterion. Specifically, the 8 h max metric was estimated on days with at least 18 of 24 valid 8 h moving averages, which were calculated from at least 6 valid hourly values.ation: