Air Toxics

Toxic air pollutants, also referred to as air toxics or hazardous air pollutants (HAPs), are chemicals that, at sufficient concentrations and exposures, are known or suspected to cause cancer. They can also cause other serious health problems or cause adverse environmental effects. DNREC monitors Delaware’s air for air toxics and publishes regular Air Toxics Strategic Plans detailing activities being undertaken by the department and its partners to reduce the risk of adverse health effects caused by the inhalation of air toxics.


Valerie Gray
Division of Air Quality

Air Toxics Questions & Answers

The air toxic pollutants of greatest concern are those that are released to the air in amounts large enough to create a risk to human health and in which many people may be exposed.

Air toxic pollutants may exist as particles or gases. Air toxics that exist as particles can include heavy metals, such as cadmium, mercury, chromium, and lead compounds, as well as organic compounds, such as polycyclic aromatic hydrocarbons (PAHs), which are emitted during the combustion of fossil fuels and wastes. Gaseous air toxic pollutants include benzene, toluene, and xylenes, found in gasoline; perchloroethylene, used in dry cleaning; and methylchloride used as a solvent by various industries.

Sources of Air Toxics

Air toxics can be produced from both stationary sources, either point or area sources, and mobile sources. Point sources include facilities that report emissions, including power plants, manufacturers, refineries, large office buildings, landfills, hospitals, incinerators, and government facilities. Smaller stationary sources or area sources include dry cleaners, printers, and automobile paint shops.  Mobile sources include both on- and off-road motor vehicles, as well as boats and aircraft. Some air toxics are released from natural sources, including volcanoes, radon gas, and emissions from forests. Although natural sources of air toxics exist, most toxics originate from man-made sources.

Studies by DNREC have found that about two thirds of the mass of emissions in Delaware came from mobile sources, about a quarter from area sources, and just under ten percent are contributed by point sources.

Studying Air Toxics in Delaware

The National Air Toxics Assessment (NATA) is EPA’s ongoing review of air toxics in the United States. EPA developed NATA as a screening tool for state, local and tribal air agencies. NATA’s results help the Division of Air Quality identify which pollutants, emission sources and places we may wish to study further to better understand any possible risks to public health from air toxics.

NATA gives a snapshot of outdoor air quality with respect to emissions of air toxics. It suggests the long-term risks to human health if air toxics emissions are steady over time. NATA estimates the cancer risks from breathing air toxics over many years. It also estimates non-cancer health effects for some pollutants, including diesel particulate matter (PM). NATA calculates these air toxics concentrations and risks at the census tract level. It only includes outdoor sources of pollutants.

The Division of Air Quality uses NATA results to learn which air toxics and emission source types may raise health risks in certain places. We can then study these places in more detail, focusing where the risks to people may be highest.

To make NATA possible, EPA must make some assumptions about the air toxics emissions data that go into it. These assumptions mean that NATA can’t give precise exposures and risks for a specific person. Instead, NATA results are best applied to larger areas – counties, states and the nation. Results for smaller areas, such as a census tract, are best used to guide follow-up local studies.

NATA calculates concentration and risk estimates from a single year’s emissions data. The risk estimates assume a person breathes these emissions each year over a lifetime (or approximately 70 years). NATA only considers health effects from breathing these air toxics. It ignores indoor hazards, contacting or ingesting toxics, and any other ways people might be exposed.

As a result, the Division must keep these limitations in mind when interpreting the results and only use the results in ways for which the assessment methods are suited.

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