EPA Prioritization:
The EPA primarily uses the results from NATA to determine what air pollution chemicals pose the greatest risk. The 1999 NATA risk specifically quantified the increased risks posed from: Cancer, and Non-Cancer (Respiratory and Neurological) health effects from 189 different chemicals (HAPs) released from background, mobile, area, or major sources. It should once again be noted that the 1999 NATA did not include the Criteria Air Pollutants as part of its evaluation as was included in the Community Prioritization.
Using the 1999 NATA data, the risk per chemical per town was averaged into a three-community average risk. Based on this review, the following HAPs pose the largest risks.
As the chart shows, the majority of health risks posed by chemicals in the 3 target communities are due to Cancer Risk. Since EPA’s goal is no more than 1 in a million at an increased risk, all the chemicals in the chart above near or exceed that goal, and thus should be considered as targets for reduction. In order to better determine what would need to change in order to target reduction of these chemicals, this project looked at how much of each of these specific chemicals came from what sources. Unfortunately the quantity data from sources was only available at the County level (as is presented in the chart below), but it is assumed the distribution for most of these chemicals would be similar at the three target community level.
Based on this distribution, it becomes clear that not only is Benzene the largest health risk contributor, but it is also the largest single chemical posing health risks emitted by sources other than background. This chart also illustrates how risk can be high when either the quantity is low – or the quantity comes from background sources cannot be easily addressed. Unfortunately, EPA did not provide the quantity estimates for background sources, while they are included in the risk analysis above, thus it cannot be distinquished easily if the small quantity from the sources above is a real risk issue or the contribution from background is the more significant risk. For instance the 2nd highest risk ranked chemical, Ethylene Dibromide, was estimated at .001 tons per year from known sources, yet a 5.49 per million risk. In reviewing EPA methodology for estimates of background concentrations – there is no estimate for Ethylene Dibromide, and thus it appears that in fact the small quantity is responsible for a large risk, since additional background quantities were not factored in.
Using EPA’s data to start prioritizing reduction opportunities – the obvious place to begin is with the chemicals that EPA has determined pose the greatest health risk in our 3 communities, and of those – the ones that have the greatest emissions from sources that can be impacted.
The first reduction priority then should be Mobile sources (both on and off road) since they are the primary contributing sources for Benzene, Butadiene and Acetaldehyde, while also contributing to Acrolein and Naphthalene emissions. Thus targeting mobile emissions would reduce 5 of the 10 top health risk chemicals identified by EPA.
Since Area Sources are the next largest contributor to the EPA identified health risk chemicals - these were explored further to determine reduction priorities.
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