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Air Toxics Data Analysis

Air toxics, also known as hazardous air pollutants, are those pollutants that are known or suspected to cause cancer and other serious health effects, or adverse environmental conditions. Although there are natural sources of air toxics such as wildfires, primary emission sources include mobile sources such as motor vehicles; stationary industrial sources; small area sources such as auto refinishing shops and drycleaners; and indoor sources such as chemicals used for cleaning.

IDEM operates a network of air toxics monitoring sites to collect and analyze air samples for toxic compounds released by these various sources. The Air Toxics Program utilizes IDEM’s air toxics monitoring data to glean information about how air toxics may be affecting air quality in Indiana’s local neighborhoods and communities. IDEM’s projects, referred to as ToxWatch, generally involve the statistical analysis of average concentrations of compounds developed over a given period of time and a comparison of these numbers to information about the toxicity of compounds and established screening levels.

  • ToxWatch Monthly Screening:
    • Each month IDEM performs a routine screening to check for unusually high readings at Indiana’s air toxics monitors to see if any immediate action is necessary to protect human health and the environment. The ToxWatch monthly screening involves comparing the concentrations recorded for the month against a set of screening levels calculated by IDEM each year. Although IDEM does compare the readings to health protective levels, the primary screening levels for the ToxWatch Monthly Screening project are based on five years of historical concentrations of each pollutant at each monitoring location to find outliers (levels that are out of the mainstream). IDEM uses a non-parametric outlier test for this analysis. The test is set up to identify readings that are roughly two standard deviations above the mean, or average. Standard deviation is the difference between the outlier and the average concentration over five years. Non-parametric describes a type of statistical analysis that does not require assumptions about the distribution for the set of data from which the sample came. IDEM has been performing these regular monthly screenings of the ToxWatch data since 2008 and has yet to encounter an event that required immediate action.
  • ToxWatch Data Analysis:
    • The ToxWatch Data Analysis Report is the Air Toxics Program’s periodic analysis of air toxics data over a multi-year timeframe. In 2018 IDEM released the ToxWatch Data Analysis containing a decade’s worth of air toxics monitoring results from 2006 to 2015. This report looked at trends in the data and compared concentrations to health protective data. A previous report covering the timeframe from 1999 to 2008 [ZIP] is also available.

IDEM also screens for potential problems from air toxics utilizing air models, which are mathematical simulations of air quality that scientists generate using approved computer programs. Where monitoring or modeling data screenings indicate potential problems in a neighborhood or community, the Air Toxics Program conducts air risk assessments to further investigate air toxics concentrations, potential emission sources, how the public may be exposed, the toxicity of the chemicals of concern, what if any increased health risks may exist, and what if any emission reductions may be needed to protect public health and the environment.

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