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Air Quality

Air Pollutants - Ozone - Forecasting and Monitoring

Historical Ozone Monitoring Data and Trends

The monitoring network has recorded a steady decline in maximum ozone concentrations in South Carolina over the past ten years. A significant portion of this improvement occurred between 2002 and 2005, as a result of cleaner engines, cleaner fuels, and better industrial controls.

Improvements in air quality have lead to reduced ozone concentrations. On average, statewide maximum daily ozone concentrations have decreased 21% from 2000 to 2009, due in large part to the cooperative efforts of state agencies, local governments, and industry to control NOX emissions. However, as scientists gain a better understanding of the health and environmental effects of ozone, the EPA has continued to lower the ozone standard. Therefore, cooperative efforts will need to be continued to ensure that South Carolina meets the ozone National Ambient Air Quality Standards.

Ozone Design Values

Every year, a design value is calculated for each monitoring site and compared to the National Ambient Air Quality Standard for the air pollutants it monitors. The design value for ozone is the average of the fourth highest daily maximum 8-hour ozone concentrations for each year over a three year period. For example, a monitoring site's design value for 2009 is the average of the fourth highest 8-hour ozone concentrations from 2007, 2008, and 2009. See the fourth highest ozone concentrations and calculated design values for each monitoring site since 2000 below.

Statewide Ozone Design Value Trends (2000 - 2009)

In the chart below, the blue band shows the range and trend of average South Carolina ozone design values over a ten-year period. All ozone monitoring data between 2000 and 2009 are included in the chart. Eighty percent of the monitoring sites have design values within the blue band. The middle white line is the state's average ozone design values by year.

Statewide Ozone Design Value Trends (2000 - 2009)

Is our state's air quality for ozone improving?

?? During the ten year period of 2000-2009, the total number of days with ozone values greater than 0.075 ppm in South Carolina declined. Between the years of 2000-2008, the number of exceedances dropped 81 percent. In 2009, South Carolina experienced very favorable summertime weather conditions and was able to report the concentrations of ozone was below the level of the standards throughout the state.

Does weather affect the formation of ozone?

?? Weather plays an important role in the formation of ozone. Sunshine, high temperatures, and low humidity are ideal conditions for the chemical reaction required to make ozone. Therefore, the majority of the days that have ozone concentration greater than 0.075 ppm occur during the summer months. Ozone season, when formation of ozone is more likely, is from April through October in South Carolina.

The chart to the right shows the total number of days for each month that had an ozone exceedance from 2000-2009. The summer months of June, July and August have the most days above the level of the standard. June had 118% more days above the standard than the month of April, and 176% more than the month of September. During that 10-year period, the summer months of June, July and August accounted for 62% of the total days above the standard.

Trends in Ozone Adjusted for Weather Conditions (EPA)

Do ozone levels vary depending on the day of the week?

Ozone Exceedances by the Day of the Week When the total number of days that had an ozone concentration greater than 0.075 ppm between 2000 and 2009 were tallied by day of the week, it shows over 80% of the days above the standard occurred during the work week. The greatest number of days with ozone over the standard occurred on Thursdays. The air quality was generally better on the weekends. This shows a connection to factors that include when and how much people drive, when people fuel their vehicles, the difference in demands on power plants, as well as the effect of leftover and transported ozone and the VOCs and NOX that spur new ozone formation.

For more information please contact the Bureau of Air Quality at (803) 898-4123 or by email.