Air Pollutants - Ozone - Monitoring and Forecasting
DHEC has developed an extensive ambient (outdoor) air quality monitoring network for ozone and other pollutants to:
- measure maximum expected concentrations in suburban and urban areas,
- provide background information in rural areas,
- help determine the effects of NOX and/or VOC emissions from specific sources on local ozone formation, and
- monitor interstate and intrastate transport of pollutants.
In 2011, there were 21 ozone monitors strategically located in 17 counties throughout the state. DHEC chose the location for each monitor in accordance with EPA monitor-siting requirements found in the Code of Federal Regulations Title 40, Part 58, Appendix E.
Monitors are located across the state to measure ozone throughout each day. Ozone monitors work on the basic principle that ozone absorbs specific wavelengths of ultraviolet (UV) light. Monitors determine ozone concentrations by comparing the difference in intensity between a beam of light passed through ambient air, and a beam of light passed through an ozone-free sample. The monitors take measurements every 10 seconds, and average the data over an hour. A computer at the monitoring site stores the continuous data and hourly averages from the monitor, and a central automatic data polling system downloads the data from the monitoring computers each hour by an automated data polling system.
DHEC only uses monitors that are designated Federal Equivalent Methods and all use UV photometry. DHEC calibrates monitors with an ozone transfer standard, we regularly check them to assure that they are providing accurate measurements. During calibration, DHEC staff determine calibration constants that convert the monitor output to actual concentration.
Monitors are calibrated with an ozone transfer standard and regularly checked to assure they are providing accurate measurements. Calibration constants that convert the monitor output to actual concentration are determined during the monitor calibration.
EPA determines the minimum number of ozone monitors that can adequately represent an area based on the Metropolitan Statistical Area (MSA) most recently measured ozone concentrations and its population. The MSA may include heavily populated counties and the adjacent counties that are closely related economically. The image below shows the MSAs in our state as of January 1, 2010.
In South Carolina, the smaller MSAs with populations less than 350,000 are required to have one ozone monitor. Larger MSAs, with populations greater than 350,000, are required to have at least two monitors. EPA requires DHEC to operate its ozone monitoring network during the months when ozone formation is more likely, often called the "ozone season," which runs from April 1 through October 31.
For more information please contact the Bureau of Air Quality at (803) 898-4123 or by email.