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 asa tracer to describe the exposure for these specific compounds. NOx are considered to be a better tracer than CO, because NOx or NOx values exist for many places over a long time, while CO is measured mostly in streets with high concentrations. Ar 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 mu g/m(3) 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.
