Frequently Asked Questions

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Air monitors are operated throughout the state to measure the concentrations of pollutants in the ambient air. Ambient refers to air that is outside of homes and businesses and that the public breathes. The Clean Air Act requires the U.S. Environmental Protection Agency (EPA) to set national ambient air standards for pollutants considered harmful to public health and the environment. Those are called the “criteria” pollutants.
The S.C. Department of Health and Environmental Control (DHEC) is responsible for operating the air monitoring network in South Carolina. Pollutant concentrations are measured using either samplers that collect pollutants, which are then analyzed in a laboratory, or monitors that can analyze and report the concentrations almost immediately.
Once the monitoring data is collected, it is checked for quality and accuracy. DHEC places all data in a national database where it is available for use by government, scientists and the public. Some preliminary measurements are available within hours on the EPA AirNow and DHEC web sites.
Visit DHEC’s South Carolina Ambient Air Monitoring map to see the location of all the air quality monitoring stations in South Carolina. Click on a location to bring up a description of the monitoring site and an explanation of what we are measuring at that location. The map also provides historical graphs showing concentrations of major pollutants found at each monitoring station.
Each monitor provides data that indicate pollutant concentrations in an area that may range from a very small area to many miles across. This is called the “scale” of the monitor. Monitor scales in the South Carolina network range from “microscale” of 10 to 300 feet across, to “regional scale,” which represents air quality in an area of thousands of square miles. Each monitor at a site has an associated scale, and the scales may be different for different pollutants at the same location.
The location of a monitor is determined by the question(s) to be answered. The air sampled must be representative of the area (and/or similar areas). Local sources and exposure are important but practical matters like site access, security, availability of utilities and cost play a role in the final selection. Minimum requirements are established by EPA for each pollutant, objective and monitoring scale to make sure the data is not unduly influenced by pollution sources.

The EPA has determined a minimum number of monitoring sites that must be established and maintained for each pollutant. DHEC annually reviews the monitoring network to make sure the minimum requirements and the needs of the air program are met. If changes are needed in the network to meet new requirements, address new questions or redirect resources, then those changes are made available for public review and EPA approval in the Annual Ambient Air Network Monitoring Plan.

South Carolina also monitors air in smaller towns and cities where EPA does not require monitoring in order to make sure the network fairly represents all of South Carolina’s air quality.

Special studies are done when there are specific questions that need to be answered for an area or type of pollutant source.

Yes, monitors can be moved for specific reasons. A monitor might be moved because of changes in the area around the site that make the location less representative. There are scientific and regulatory reasons to try to maintain a fixed site for as long as possible. One of the goals of an ambient air monitoring network is to track trends and progress. Many of the national standards require several years of data at one location to account for the impact of “unusual” years or events.

Weather patterns can change from year to year (El Nino, droughts, etc.) and operating a monitoring site for several years is needed to understand typical air quality in that area. The year-to-year changes related to the weather can make changes in pollutant concentrations hard to see unless there is a long, consistent data record. If monitors are moved often, even within the same area, it is very difficult to know if any concentration differences are caused by something at the site or a change in the weather.

It is not necessary for a monitor to be located in every county to have an idea of the local air quality. Monitoring is focused on the areas where pollutant concentrations are expected to be highest, so areas with fewer sources of air pollution are expected to have better air quality. Monitors in larger areas are checked to be sure they accurately represent the air quality. For example, DHEC is aware that a couple of ozone monitors reasonably represent the rural coastal plain because DHEC has monitored places in- between to confirm similar concentrations and patterns.

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