Are there differences between the calculations for determining NAAQS attainment and the EPHT air quality indicator for PM2.5?
Yes. The calculation for the EPHT air quality indicator for PM2.5 is based on the exceedances of daily or annual PM2.5 NAAQS in a county over a one year period whereas the calculation for determining NAAQS attainment is based on the 3-year annual average of the quarterly mean PM2.5 concentrations or a 98th percentile value for the daily PM2.5 NAAQS over a three year period. The air quality indicator is based on monitoring data submitted by the MassDEP to US EPA’s Air Quality System, or AQS (http://www.epa.gov/ttn/airs/airsaqs/). EPHT data may also include air quality monitoring results during “exceptional events”, whereas the US EPA allows states to exclude certain “exceptional events” when assessing NAAQS attainment. Exceptional events may include chemical spills and industrial accidents, structural fires, and natural events (volcanoes and earthquakes, high wind events, wildfires). For example, data for several 2002 PM2.5 exceedances was flagged as an “exceptional event”, because they
