Category,Definition "Carbon Monoxide (CO)" " CO 2nd highest 1-hour","Second highest one-hour carbon monoxide measurement in the year" " CO 2nd highest non-overlapping 8-hour average","Second highest non-overlapping 8-hour carbon monoxide average in the year" "Nitrogen Dioxide (NO2)" " Lead maximum all rolling 3-months average","The maximum of all rolling 3-month averages for lead in the year" " NO2 98th percentile of daily maximum 1-hour","Nitrogen dioxide, the 98th percentile of the daily max one-hour measurements in the year" " NO2 annual mean of 1-hour","Nitrogen dioxide, the annual mean of all the one-hour measurements in the year" Ozone " Ozone 2nd highest daily maximum 1-hour","Second highest maximum one-hour ozone measurement in the year" " Ozone 4th highest daily maximum 8-hour average","4th highest non-overlapping 8-hour ozone average in the year" "Particulate Matter (PM)" " PM 2.5 98th percentile of daily average","The 98th percentile of the daily average PM2.5 measurements in the year" " PM 2.5 weighted (by quarter) annual average","The weighted annual mean (mean weighted by calendar quarter) for PM2.5 for the year" " PM10 2nd highest 24-hour average","The second highest 24-hour average measurement for PM10 in the year" " PM10 average 24-hour","The weighted annual mean (mean weighted by calendar quarter) for PM10 for the year" "Sulfur Dioxide (SO2)" " SO2 2nd highest 24-hour average","Second highest 24-hour average sulfur dioxide measurement in the year" " SO2 99th percentile of daily maximum 1-hour","The 99th percentile of the daily maximum 1-hour sulfure dioxide measurements in the year" " SO2 annual mean of 1-hour","Annual mean of all the 1-hour sulfur dioxide measurements in the year"