Ozone Smog Analysis

Clean Air Task Force’s Gasping for Breath report estimates health effects that can be attributed to elevated ozone levels linked to air pollution from oil and gas facilities. The analysis in the report is based on EPA’s projection of 2025 emissions from EPA’s National Emissions Inventory.

How the Analysis Was Performed

We created two cases: one with and one without emissions from oil and gas facilities. By comparing the modeled ozone concentration levels in these two cases, we determined the health impact that can be directly attributed to the oil and gas industry. We ran both of these cases through an atmospheric model (CAMx). Finally, we calculated ozone season health impacts associated with the ozone concentrations using EPA’s Benefits Mapping and Analysis Program (BenMAP).

The approach used to calculate benefits in this study follows the same methodology as the US EPA’s Regulatory Impact Analysis (RIA) developed in support of the most recent update to the National Ambient Air Quality Standards (NAAQS) for ozone. We estimate the following health impacts associated with changes in ozone concentration during the ozone season (May 1-Sept 30, see below for explanation):

  • Asthma attacks
  • School Loss Days
  • Asthma-related emergency department visits
  • Respiratory-related hospital Admissions
  • Acute respiratory symptoms (MRAD)

Ozone Season

“Ozone season” is the 5 month period from May 1 through September 30th. We present ozone season health impacts rather than annual health impacts because this was the approach used by EPA in its 2015 NAAQS RIA. In addition, most of the health studies focus on the summer season only, and most of the high ozone days take place during the ozone season.

Impact vs Risk

The ozone health impact data is presented in terms of total number of asthma attacks, lost school days, etc. In contrast, the air toxics health risk data is presented in terms of risk per million people exposed. Thus, small changes in ozone smog concentrations in areas with large total populations can have a large total health impact numbers. However, small health impact numbers in rural or more sparsely populated areas does not indicate a lower health risk, it simply reflects a smaller total number of incidents.

Mapping Asthma

The ozone layer on the Threat Maps shows “bubbles” of varying sizes depending on the number of asthma attacks in the county or metropolitan area. On the map, the bubble is placed in the geographical center of the area, and it does not not reflect the exact location of asthma attack risk. (The exception to this is Los Angeles, in which the bubble is placed in Los Angeles County rather than in the geographical center of the metropolitan area).

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