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About DHEC

Toxic Air Pollutants

What are Toxic Air Pollutants?

Toxic air pollutants are those pollutants that are known or suspected to cause cancer or other serious health effects, such as reproductive effects or birth defects, or adverse environmental effects. They take the form of liquids, solids and gases. Toxic Air Pollutants include 187 pollutants designated by EPA as Hazardous Air Pollutants along with an additional 69 pollutants identified in SC State Regulations as Toxic Air Pollutants. Examples of Toxic Air Pollutants are benzene, dioxin, and mercury.

Scientists estimate that millions of tons of toxic pollutants are released into the air each year. Most Toxics Air Pollutants originate from manmade sources, including both mobile sources (e.g., cars, buses, trucks) and stationary sources (e.g., factories, refineries, power plants). However, some are released in major amounts from natural sources such as forest fires.

Efforts to Reduce Toxics Air Pollutants


Although Toxic Air Pollutants are emitted from many sources, the vast majority of regulatory requirements for these substances focus on industrial and commercial sources. As required by the Clean Air Act, EPA identified a list of Hazardous Air Pollutants to be regulated, identified the industrial and commercial sector categories that emit these pollutants and developed standards to control emissions from these sector categories. These standards, called Maximum Achievable Control Technology (MACT) standards are based on the best emission controls being achieved by industry. Over 100 standards have been developed by EPA and over 50 of these standards apply to industrial and commercial sources operating in South Carolina. Examples of these sources are pulp and paper mills, chemical plants, and wood products plants. EPA has estimated that these rules reduce annual emissions of nearly 200 different air toxics by about 1.7 million tons. In addition to federal standards, SC has a state air toxic regulation that limits the concentration of Toxic Air Pollutants at the facility's boundaries.

EPA requirements to reduce Hazardous Air Pollutants are not a one-time occurrence. After standards have been in effect for 8 years, EPA determines if the standard protects public health adequately. If the standard is not protective, EPA adopts more stringent standards after considering costs, energy, safety and other factors. Every 8 years the EPA is required to review the standards and revise them as necessary taking into account new/updated pollutant reduction practices or technologies.

Area Sources

Smaller industrial sources emitting Hazardous Air Pollutants are called Area Sources. EPA identified a total of 70 area source categories and finalized the last of these rules in March, 2011. SC is in the process of implementing these new rules that apply to a large number of commercial and industrial sources, including many sources that do not have air permits.


There have been several efforts to specifically reduce mercury emissions. Some of the Hazardous Air Pollutant standards mentioned above require the reduction on mercury emissions from significant mercury sources. Examples of sources required to reduce mercury emissions are electric arc furnaces; commercial, industrial, and institutional boilers; power plants, and commercial and industrial solid waste incineration units. There are over 300 large industrial boilers located at 70 facilities in SC. There are also several hundred smaller boilers subject to the area source boiler standards. After March 2014, boilers located at area sources will be required to better control their mercury emissions, along with other HAP emissions. Boilers located at major sources will be required to control their mercury emissions by January 2016. The rule covering over 25 utility boilers located at the 12 power plants will be effective by April 2015.

In addition, efforts to identify ways to decrease the amount of mercury in South Carolina's environment continue to be a priority. The S.C. Mercury Assessment and Reduction Initiative, which began in 2008, focuses on the assessment and reduction of mercury emissions, continued and enhanced risk communication, and increased recycling of mercury-containing products. The S.C. Mercury Assessment and Reduction Initiative, published in 2010, discusses assessment, monitoring and reduction efforts and recommends actions to accomplish those and other related goals. More information on this initiative can be found at:

Mobile Sources

A recent EPA rule reduces hazardous air pollutants from mobile sources by limiting the benzene content of gasoline and reducing toxic emissions from passenger vehicles and gas cans. SC actively participates in the Southeast Diesel Collaborative (SEDC), which is a voluntary partnership between EPA, States, and other public and private entities and is intended to promote opportunities to reduce diesel emissions. The SEDC also promotes the use of biodiesel because of its air quality benefits including the reduction of many mobile source air toxic compounds. The reduction of emissions from diesel engines is in important component of this effort. Over $11 million worth of projects are being implemented in SC using $6.2 million of federal funding from Clean School Bus USA and Diesel Emission Reduction Act (DERA) grants and $4.8 million in participant matching funds. Projects awarded under the state DERA program administered by DHEC have estimated reductions of 2000 tons of NOx and 78 tons of PM over the lifetime of the equipment.

Co-Benefit Reductions

Rules requiring the reduction of Toxic Air Pollutants have the added benefit of reducing Criteria Pollutants such as ozone and particulate matter. This occurs because some Toxic Air Pollutants are also ozone-causing volatile organic compounds (e.g., toluene) or particulate matter. In addition, some of the technologies and practices designed to control air toxics also reduce pollutants that are not currently among the 187 listed Hazardous Air Pollutants

Tracking Toxic Air Pollutants

Unlike Criteria Pollutants, there are no national ambient air concentration standards for Toxic Air Pollutants, making it difficult to assess the overall ambient impact in SC. The state tracks actual Toxics Air Pollutant emissions from industrial sources. These emissions are reported as part of the Emissions Inventory reporting every 3 years. Certain industrial sources must also report annually their emissions of listed Toxic Air Pollutants as a part of the national Toxics Release Inventory.