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Air toxics: modeling

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Modeling is a process that uses computers and math to estimate air pollution and associated human health exposures. Dispersion modeling is a type of modeling that estimates how air pollution will likely spread out over an area based on a variety of different factors.

Dispersion models such as AERMOD, can combine reported or measured air toxics emission rates from individual sources with local meteorological data and other facility information such as stack height and boundary to fenceline to estimate the ambient concentrations of each pollutant. 

Illustration of AERMOD dispersion model output showing emission sources and pollution locations

Photo of AERMOD View provided by Lakes Software.

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Exposure models such as the human exposure model (HEM) or the hazardous air pollutant exposure model (HAPEM) can use these ambient air concentrations to predict potential human exposures. These models can give us information to assess potential risk for cancer and non-cancer health effects from air toxics. 

By applying the HAPEM model to nationally available emission and meteorological datasets, the EPA has developed a national screening tool called AirToxScreen to characterize health risks from over 100 different air toxics across the country. Colorado Department of Public Health and Environment uses AirToxScreen results to prioritize places for more detailed follow-up investigations. This follow-up work may include site- or community-specific studies. For example, in 2018 AirToxScreen showed elevated health risks from ethylene oxide emissions at a commercial sterilizer in Lakewood, Colorado and the department initiated more detailed investigations.

EPA applies the HEM model during a part of the rulemaking processes for the National Emission Standards for Hazardous Air Pollutants (NESHAP). HEM estimates potential health risks for cancer and non-cancer health effects on communities in close proximity to specific facilities subject to the regulations. These estimated risks inform decisions about what types of air pollution control strategies may be required.