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RELATIONSHIPS OF INDOOR, OUTDOOR, AND PERSONAL AIR (RIOPA). PART I. COLLECTION METHODS AND DESCRIPTIVE ANALYSES
Impact/Purpose:
Urban populations are exposed to a complex mixture of possibly toxic pollutants generated and emitted by a variety of outdoor and indoor sources. These pollutants occur naturally or result from human activities; they may be present in the form of gases, liquid droplets, or solid particles. The US Environmental Protection Agency (EPA) defines an air toxic as any substance known or suspected to cause harm to humans or the environment. The Clean Air Act Amendments of 1990 list 188 air toxics as hazardous air pollutants; these include volatile organic compounds (VOCs), carbonyls (aldehydes and ketones), and components often associated with particulate matter (PM). The Amendments require the EPA to evaluate the possible health risks from air toxics and, if appropriate, control their ambient levels. To achieve this objective, the EPA identified pollutants that may be most hazardous to health and categorized them as urban air toxics (emitted from all sources) or mobile-source air toxics; some pollutants appear on both lists. Currently, the EPA regulates ambient levels of fine PM through the National Ambient Air Quality Standards for PM2.5 (PM of 2.5 µm or smaller).
Understanding personal exposures to both air toxics and PM—and how different sources contribute to individual exposures—has been considered an important first step in assessing the possible public health risks from these species in the urban environment. The Relationships of Indoor, Outdoor, and Personal Air (RIOPA) study was designed to provide such information for a large number of VOCs and carbonyls, including some that are listed as urban and mobile-source air toxics, and for PM2.5.
Urban populations are exposed to a complex mixture of possibly toxic pollutants generated and emitted by a variety of outdoor and indoor sources. These pollutants occur naturally or result from human activities; they may be present in the form of gases, liquid droplets, or solid particles. The US Environmental Protection Agency (EPA) defines an air toxic as any substance known or suspected to cause harm to humans or the environment. The Clean Air Act Amendments of 1990 list 188 air toxics as hazardous air pollutants; these include volatile organic compounds (VOCs), carbonyls (aldehydes and ketones), and components often associated with particulate matter (PM). The Amendments require the EPA to evaluate the possible health risks from air toxics and, if appropriate, control their ambient levels. To achieve this objective, the EPA identified pollutants that may be most hazardous to health and categorized them as urban air toxics (emitted from all sources) or mobile-source air toxics; some pollutants appear on both lists. Currently, the EPA regulates ambient levels of fine PM through the National Ambient Air Quality Standards for PM2.5 (PM of 2.5 µm or smaller).
Understanding personal exposures to both air toxics and PM—and how different sources contribute to individual exposures—has been considered an important first step in assessing the possible public health risks from these species in the urban environment. The Relationships of Indoor, Outdoor, and Personal Air (RIOPA) study was designed to provide such information for a large number of VOCs and carbonyls, including some that are listed as urban and mobile-source air toxics, and for PM2.5.
Description:
The homes and subjects selected did not proportionally represent the greater population. Rather, homes close to sources were preferentially sampled in order to examine the impact of possibly high exposures. In addition, the characteristics of the subjects and the homes differed among cities. Thus comparing results among the three areas, extrapolating the numeric results obtained in this study to the general population, or attributing them to a given city or region must be considered with caution.
The analyses of the aggregate data suggest some trends that will need to be verified with more detailed analyses. With a few exceptions, mean and median personal exposure and indoor concentrations of VOCs and carbonyls were higher than the outdoor concentrations within each city and for the whole data set. Personal PM2.5 concentrations were higher than indoor and outdoor concentrations. The finding that personal exposure concentrations were higher than outdoor concentrations for many compounds indicates that indoor sources contribute to, and in some cases dominate, personal exposures; this is consistent with results from other studies.
Several VOCs were present only at low levels in all environments and were not detected in many outdoor samples. The species detected in more than 60% of outdoor samples common to all three cities were MTBE, carbon tetrachloride, benzene, ethyl benzene, m- & p-xylenes, and o-xylene. MTBE had the highest outdoor concentrations. Although cities with different types of sources were chosen and homes near sources were preferentially sampled, the ranges of outdoor VOC concentrations were generally similar in the three cities. The median outdoor concentrations of carbonyls were more variable than VOCs across the cities (with the exception of formaldehyde).
Indoor concentrations of several VOCs and carbonyls differed among cities. The species with the highest indoor concentrations were the VOCs MTBE, toluene, a-pinene, and d-limonene and the carbonyls formaldehyde, acetaldehyde, and acetone. Personal exposure concentrations for several VOCs and some carbonyls also differed among cities.
Among the three cities, differences in indoor and outdoor PM2.5 levels were slight, but differences in personal PM2.5 exposures were more pronounced.
The analyses of the outdoor contributions to indoor air suggested that some VOCs (MTBE, benzene, carbon tetrachloride, and trichloroethylene) were primarily generated outdoors and contributed 90% to 100% of the indoor concentrations. Outdoor concentrations of other VOCs (chloroform, a-pinene, ß-pinene, and d-limonene) and most carbonyls (including formaldehyde, acetaldehyde, and hexaldehyde) contributed less to indoor air (13% to 43% of indoor concentrations). The carbonyls that contributed most were acrolein, crotonaldehyde, and propionaldehyde (50% to 63%). For PM2.5, outdoor air contributed 60% of the indoor concentration.