Human exposure to urban air pollution

Our plain-English summary of Human exposure to urban air pollution, by C.E. Boström, J. Almén, B. Steen, et al (Environmental Health Perspectives, 1994).

The study

• Authors: C.E. Boström, J. Almén, B. Steen, R. Westerholm
• Journal: Environmental Health Perspectives
• Published: 1994;102 Suppl 4(Suppl 4):39-47
• Type of article: Review
• Cited by: 40 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

This study deals with some methods of making human exposure estimates, aimed at describing the human exposure for selected air pollutants in Sweden that are suspected carcinogens. Nitrogen oxides (NOx) have been chosen as an indicator substance for estimating the concentration of the urban plume. Earlier investigations have shown that the traffic in Swedish cities contributes around 85% to the measured NOx concentrations, and that most of the mutagenicity in urban air originates from traffic. The first section of this paper describes measurements in Stockholm of some unregulated light hydrocarbons, such as ethene, ethyne, propane, propene, butane, and isobutane. In addition, measurements of some volatile aromatic hydrocarbons are presented. Simultaneous measurements of carbon monoxide (CO) were made. The ratios between CO and the individual specific compounds were determined by linear regression analysis. By analysis of relationships between CO and NOx, NOx concentrations can be used as a tracer to describe the exposure for these specific compounds. NOx are considered to be a better tracer than CO, because NOx or NO2 values exist for many places over a long time, while CO is measured mostly in streets with high concentrations. At low concentrations, instruments that measure normal CO levels give no detectable signals. Through use of atmospheric dispersion models and models that describe how people live and work in urban areas it has been possible to describe the average exposure to NOx in cities of different sizes. The exposure to NOx for people living in the countryside has also been estimated. In this way, it has been possible to calculate the average exposure dose for NOx for the Swedish population. This figure is 23 micrograms/m3. By use of the relationships between NOx and specific compounds the average dose has been calculated for the following compounds: polyaromatic compounds (PAH); ethene, propene, and butadiene; benzene, toluene, and xylene; formaldehyde and actaldehyde; nickel, chromium (VI), arsenic, and cadmium; asbestos; and silicon.

In plain English

This study estimated the average Swedish person's exposure to several suspected cancer-causing air pollutants. The authors did not measure each pollutant everywhere. They used nitrogen oxides (NOx), which in cities come mostly from traffic, as a tracer. They combined city-center NO2 data with models of where people live and travel, then applied measured or estimated NOx-to-pollutant relationships, some resting on assumptions or data from elsewhere. Average NOx exposure for the Swedish population of 8.5 million was estimated at 23 micrograms per cubic meter. For asbestos, the only outdoor measurement in Sweden the authors knew of was made in Stockholm in 1981. It found 3,000 fibers per cubic meter or lower by optical microscope and 9,000 to 10,000 by electron microscope. From this they estimated a national average of 200 optically detectable and 5,000 electron-microscopically detectable fibers per cubic meter. They said the error may be very large, guessing a factor of 5. The article did not name an asbestos fiber type. The authors concluded that exposure to mutagenic air pollutants is not a problem only for large cities.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Population exposure-estimation (modeling) study using NOx as a tracer for traffic-related pollutants. It was based on NO2 measurements in the central parts of 60 Swedish cities, correction factors, and measured or estimated pollutant-to-NOx relationships.
• Who was studied: The Swedish population (8.5 million inhabitants). Supporting air measurements came from Stockholm (December 1986 to August 1987), Gothenburg and other Swedish cities.
• Exposure: Ambient (outdoor) urban and rural air pollutants: NOx, light hydrocarbons, PAH, benzene, toluene, xylene, aldehydes, metals, silicon, butadiene and asbestos fibers. The asbestos fiber type was not specified.
• Main results:
  • Estimated mean NOx exposure for the Swedish population was 21 micrograms per cubic meter. This rose to 23 micrograms per cubic meter when travelers' exposure in Stockholm and Gothenburg was added.
  • In the 1981 Stockholm measurement, asbestos fibers detectable by optical microscope numbered 3,000 per cubic meter or lower.
  • In the same Stockholm measurement, analysis by electron microscope gave 9,000 to 10,000 fibers per cubic meter.
  • Estimated mean population exposure to asbestos in Sweden was 200 optically detectable fibers per cubic meter and 5,000 electron-microscopically detectable fibers per cubic meter.
  • In central Stockholm, heavy-traffic sites had 5 to 10 times higher concentrations of all measured hydrocarbons than low-traffic sites.
  • In Gothenburg, PAH concentrations were three to five times higher in winter than in summer.
  • Half of the population's NOx exposure-dose was received in cities and urban areas with fewer than 50,000 people.
• The authors' conclusion: The authors concluded that exposure to mutagenic air pollutants is not a problem only for large cities. They said more systematic measurements of genotoxic substances in urban areas are needed.
• Limitations the authors state:
  • The error in the asbestos estimate may be very large; the authors guessed a factor of 5.
  • Much of the data needed to estimate exposure to mutagenic substances was lacking.
  • The butadiene-to-NOx ratio was based on a North American database, not Swedish measurements.
  • The share of chromium that is hexavalent was not known and had to be assumed.
  • The method estimates exposure through inhalation only, not intake through food.
  • No systematic determination of indoor versus outdoor concentrations had been made for Sweden.

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