Issue link: https://blog.providence.org/i/1367407
PolicyLink and PERE 113 An Equity Profile of Orange County Air pollution data and analysis The air pollution exposure index referred to on pages 88-89 is derived from the 2011 National-Scale Air Toxics Assessment (NATA) developed by the U.S. Environmental Protection Agency. The NATA uses general information about emissions sources to develop risk estimates and does not incorporate more refined information about emissions sources, which suggests that the impacts of risks may be overestimated. Note, however, that because that analysis presented using this data is relative to the United States overall in the case of exposure index, the fact that the underlying risk estimates themselves may be overstated is far less problematic. The NATA data include estimates of cancer risk and respiratory hazards (non-cancer risk) at the census-tract level based on exposure to outdoor sources. It is important to note that while diesel particulate matter (PM) exposure is included in the NATA non-cancer risk estimates, it is not included in the cancer risk estimates (even though PM is a known carcinogen). Data and methods The index of exposure to air pollution presented is based on a combination of separate indices for cancer risk and respiratory hazard at the census-tract level, using the 2011 NATA. We followed the approach used by the U.S. Department of Housing and Urban Development (HUD) in developing its Environmental Health Index. The cancer risk and respiratory hazard estimates were combined by calculating tract- level z-scores for each and adding them together as indicated in the formula below: = − + − Where c indicates cancer risk, r indicates respiratory risk, i indexes census tracts, and µ and σ represent the means and standard deviations, respectively, of the risk estimates across all census tracts in the United States. The combined tract level index, , was then ranked in ascending order across all tracts in the United States, from 1 to 100. Finally, the tract-level rankings were summarized to the city, county, and higher levels of geography for various demographic groups (i.e., by race/ethnicity and poverty status) by taking a population-weighted average using the group population as weight, with group population data drawn from the 2015 5-year ACS summary file. For more information on the NATA data, see http://www.epa.gov/national-air-toxics- assessment.