Improvement in Air Quality

The chart below presents the number of exceedances of the one-hour ozone standard which have occurred in the St. Louis area since 1997 and the number of days which had meteorological conditions favorable for the formation of ozone. It can be observed that over time, the implement of regional control strategies have contributed to the reduction in the number of exceedances while the number of ozone conducive days has remained relatively the same. This chart was developed based on information from the Missouri Department of Natural Resources and the Illinois Environmental Protection Agency.

Criteria for an ozone conducive day are: temperatures greater than 85 degrees Farenheit; wind speeds less than 10 miles per hour; solar radiation of 500 Langleys or better (Langley is a measurement unit); little or no daytime precipitation; and winds from southeast to west.

The second chart shows the number of exceedances of the one-hour ozone standard from 1984-2001 and the start dates for transportation-related control strategies in the Missouri portion of the St. Louis region. These strategies include the vehicle emissions inspection and maintenance (I/M) program, vapor recovery at service stations and clean fuels program (low volatility gasoline and Reformulated Gasoline program). This chart is based on information from the Missouri Department of Natural Resources.