RESEARCH REPORT

Do socioeconomic characteristics modify the short term association between air pollution and mortality? Evidence from a zonal time series in Hamilton, Canada

M Jerrett¹, R T Burnett², J Brook³, P Kanaroglou¹, C Giovis¹, N Finkelstein¹ and B Hutchison⁴

¹ School of Geography and Geology and McMaster Institute of Environment and Health, McMaster University, Hamilton, Ontario, Canada
² Health Canada
³ Environment Canada
⁴ Centre for Health Economics and Policy Analysis and Department of Clinical Epidemiology and Biostatistics, McMaster University

Correspondence to:
Correspondence to:
Professor M Jerrett
Biostatistics Division, Department of Preventive Medicine and Department of Geography, University of Southern California, 1540 Alcazar Street, CHP-220, Los Angeles, CA 90089-9011, USA; jerrettm{at}mcmaster.ca

Study objective: To assess the short term association between air pollution and mortality in different zones of an industrial city. An intra-urban study design is used to test the hypothesis that socioeconomic characteristics modify the acute health effects of ambient air pollution exposure.

Design: The City of Hamilton, Canada, was divided into five zones based on proximity to fixed site air pollution monitors. Within each zone, daily counts of non-trauma mortality and air pollution estimates were combined. Generalised linear models (GLMs) were used to test mortality associations with sulphur dioxide (SO₂) and with particulate air pollution measured by the coefficient of haze (CoH).

Main results: Increased mortality was associated with air pollution exposure in a citywide model and in intra-urban zones with lower socioeconomic characteristics. Low educational attainment and high manufacturing employment in the zones significantly and positively modified the acute mortality effects of air pollution exposure.

Discussion: Three possible explanations are proposed for the observed effect modification by education and manufacturing: (1) those in manufacturing receive higher workplace exposures that combine with ambient exposures to produce larger health effects; (2) persons with lower education are less mobile and experience less exposure measurement error, which reduces bias toward the null; or (3) manufacturing and education proxy for many social variables representing material deprivation, and poor material conditions increase susceptibility to health risks from air pollution.

Abbreviations: GLM, generalised linear model; CoH, coefficient of haze; SO₂, sulphur dioxide; NT, non-trauma; AIC, Akaike information criterion; CT, census tract; MPC, mean percentage change

Keywords: air pollution; mortality; acute effects; socioeconomic factors; GIS

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