*Monthly number of days on which one or more Basin locations exceeded one or more federal standards. The standards were exceeded on a total of 116 days in 1995.
**The number of exceedances due to PM10 alone may have been higher, since PM10 samples are only collected every sixth day.
Although concentrations of pollutants exceeding the standards were recorded frequently in the Basin in 1995, the number of exceedances recorded varied with time of year. Figure 3 shows the number of days exceeding the federal standards in the Basin during each month of 1995. Ozone exceedances peaked during the summer, and carbon monoxide exceedances peaked during the late fall and winter. Since PM10 exceedances are relatively infrequent and samples are normally collected every sixth day, no clear pattern can be seen for PM10 in 1995. However, examination of data for the 10-year period 1985-1995 shows that exceedances of the federal PM10 standard occur with greatest frequency in the fall and winter.
Return to Air Quality and Trends Page
 AQMDHome Page |