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Bureau of Air

Chicago O’Hare Airport
Air Toxic Monitoring Program

June – December, 2000

The full report is available for download as an Adobe Acrobat PDF file.

Download the report (PDF, 890K file, 51 pages)

Executive Summary

O'Hare International Airport (O'Hare) is one of the world's busiest airports and the subject of much interest regarding the environmental impact airport operations have on the surrounding community and the Chicago area in general. As part of its fiscal year 2001 air monitoring program, the Illinois EPA measured the airborne levels of various air contaminants in the vicinity of O'Hare as well as at other locations in the Chicago area. The purpose of this measurement program was to collect information that would help assess the relative impact of airport related emissions and levels of airborne contaminants characteristic of large urban areas. This monitoring program will supplement a national program designed to assess and minimize the impact of toxic air contaminants in urban areas. The national program is referred to as the National Integrated Urban Air Toxics Strategy (National Strategy).

The National Strategy was developed by the United States Environmental Protection Agency (USEPA) in response to requirements specified in the federal Clean Air Act. Under these requirements, USEPA is charged with assessing the impact of airborne levels of various air toxic compounds on human health in urban areas of the United States and taking action to reduce risks caused by unacceptable levels of such contaminants. In July 1999, the USEPA released its National Strategy describing a framework for addressing air toxic emissions from stationary and mobile sources such as O'Hare Airport. As part of the National Strategy, air monitoring programs are to be used to identify and measure compounds believed to present the greatest concern to public health in urban areas.

Federal and State funding was provided to allow the initiation of an urban air toxic monitoring program in calendar year 2000. The funding was adequate to support a limited air quality investigation of targeted compounds through a six month monitoring program with two sites located near O'Hare Airport and three other sites in the Chicago metropolitan area. The monitoring program began in June 2000 and focused on the urban air toxic compounds identified in USEPA's National Strategy and on mobile source emissions associated with airport operations. The compounds sampled included volatile organics, semi-volatile organics, carbonyls and trace metals. The monitoring program ended in December 2000.

The Chicago area toxics monitoring program, as deployed in 2000, was designed to provide data to meet four objectives:

  1. Measure the concentrations of specific compounds of concern;
  2. Assess the geographic variability of various compounds in the Chicago area and perform a comparison of levels measured at the two O'Hare sites to those recorded at the remaining three Chicago area locations;
  3. Compare Chicago area results to data collected for other large U.S. cities; and
  4. Determine if the emissions associated with O'Hare Airport have a measurable impact on air quality in areas adjacent to the airport.

In order to measure the concentrations of the target compounds, comprehensive sampling was conducted on sixteen days through the six month period of June through December 2000, using a once every twelve days sampling schedule. The sampling results were summarized for each of the five monitoring sites and tabulated into two categories, Urban Air Toxic compounds and Hazardous Air Pollutants (HAPs). The Urban Air Toxics compounds are those identified by USEPA in the National Strategy that present the greatest threat to public health in urban areas, including known or suspected cancer risks from compounds such as benzene, formaldehyde, chromium and dioxins. The HAPs are compounds required to be regulated by USEPA under the Clean Air Amendments of 1990 that are known or suspected to cause cancer or have other serious health effects but are not included in the list of Urban Air Toxic compounds covered under the National Strategy. The HAPs measured included such compounds as ethyl benzene, styrene, toluene, xylenes and various polycyclic aromatics such as naphthalene and phenanthrene. The tabulated data included the individual daily sampling results along with the overall average concentration found for each target compound.

The program's sampling sites were located to provide air toxic measurements at different points across the Chicago metropolitan area, thereby allowing for a comparison of the levels found at O'Hare Airport to those found in different parts of the metropolitan area. In addition to the two sites located near O'Hare in Bensenville and Schiller Park, sites were also located in Northbrook, just north of the urban core, at Washington School in highly industrialized Southeast Chicago, and in Lemont, just downwind of major refineries and chemical complexes and on the southwestern edge of the metropolitan area.

A review and analysis of the accumulated monitoring results obtained from the five site monitoring network provided the following findings:

  1. The average concentrations measured at O'Hare Airport for many of the target compounds were found to be comparable with the concentrations found at the other Chicago area sites;
  2. The highest concentrations of several target urban air toxic compounds were found to be spread between several sites but generally the highest levels for many of the air toxics were found to occur in Southeast Chicago;
  3. The lowest concentrations of most target compounds were measured at Lemont.

A comparison of measured levels of urban air toxics in Chicago to those found in other large cities served as a point of reference to what would be considered "typical urban" concentrations. USEPA's Aerometric Storage and Retrieval System (AIRS) was accessed to obtain the air quality data collected from monitoring sites nationwide. A review of information submitted to AIRS found that data for certain air toxic compounds had been reported for a number of large urbanized areas. Based upon a comparison of the results from the Chicago area monitoring program to that collected for other large U.S. cities data, it was found that:

  1. Concentrations of several of the principal urban air toxics, such as acetaldehyde, benzene, and formaldehyde, compared to the metropolitan areas of Atlanta, Detroit, Houston and Milwaukee, were found to be comparable or lower in the Chicago metropolitan area.
  2. The acetaldehyde and formaldehyde levels measured near O'Hare Airport were comparable or lower than levels measured in Atlanta, Detroit and Houston.

In order to assess the possible impact of emissions from O'Hare Airport on adjacent areas, two monitoring sites were deployed on different sides of the airport. This configuration allowed for the collection of sampling data on wind persistent days that would align one site to be upwind, unaffected by the airport, and the other to be downwind and subject to airport emissions. The difference in concentrations found between the two sites on those wind-persistent days allowed for an approximation of the airport's impact. Of the sixteen sampling days, five days had such wind-persistent conditions. An analysis of the results from those five days found the downwind site to record levels of some target compounds from 20-85% higher than the upwind site. The compounds with measurable differences included acetaldehyde, benzene, formaldehyde, polycyclic organics, toluene and lead. All of those compounds have been associated with emissions from airport operations. An impact from the airport was not unexpected since airport operations are sources of various air contaminants. The concentrations measured downwind of O'Hare were at levels considered to be "typical" of an urban area and in some cases lower than values measured in other cities.

Based upon the review of the air toxics monitoring data collected near O'Hare Airport, from other Chicago area sites, and from USEPA's AIRS database, the following conclusions were reached:

  1. The levels of air toxic compounds found near O'Hare and other sites in the Chicago metropolitan area were comparable or lower than those found in other large U.S. cities.
  2. The highest levels of most air toxic compounds measured in the Chicago area were found in Southeast Chicago.
  3. An analysis of data collected from the sites at O'Hare found that emissions from the Airport have an impact on the air quality in adjacent communities, but that impact did not result in levels higher than those found in a typical urban environment.

The data collected through this study's air monitoring program indicated that the toxics air quality in the vicinity of O'Hare Airport is comparable to the air quality in other parts of Chicago and comparable to the air quality in other major urban areas. There are continuing and ongoing efforts, such as through USEPA's National Strategy, to identify, assess and reduce risk from air toxics in and around urban areas.

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