Evaluating Multipollutant Exposure and Urban Air Quality: Pollutant Interrelationships, Neighborhood Variability, and Nitrogen Dioxide as a Proxy Pollutant
BACKGROUND: Although urban air pollution is a complex mix containing multiple constituents, studies of the health effects of long-term exposure often focus on a single pollutant as a proxy for the entire mixture.
OBJECTIVES: We examined air pollutant concentrations and interrelationships at the intra-urban scale to obtain insight into the nature of the urban mixture of air pollutants. This will assist epidemiological studies that exploit spatial differences in exposure by clarifying the extent to which measures of individual pollutants, particularly NO2, represent spatial patterns in the multipollutant mixture.
METHODS: Mobile measurements of 23 air pollutants were taken systematically at high resolution in Montreal, Quebec, Canada, spread among 34 days in the summer, winter and autumn of 2009.
RESULTS: We observed variability in pollution levels and in the statistical correlations between different pollutants according to season and neighborhood. Nitrogen oxide species (NO, NO2, NOx, and NOy) had the highest overall spatial correlations with the suite of pollutants measured. Ultrafine particles (UFP) and hydrocarbon-like organic aerosol (HOA) concentration, a derived measure used as a specific indicator of traffic particles also had very high correlations.
CONCLUSIONS: The multipollutant mix varies considerably throughout the city, both in time and in space, and thus, no single pollutant would be a perfect proxy measure for the entire mix under all circumstances. However, based on overall average spatial correlations with the suite of pollutants measured, nitrogen oxide species appeared to be the best available indicators of spatial variation in exposure to the outdoor urban air pollutant mixture.