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Haidong Kan,^1,2 Stephanie J. London,² Guohai Chen,³ Yunhui Zhang,¹ Guixiang Song,⁴ Naiqing Zhao,⁵ Lili Jiang,⁴ and Bingheng Chen¹

¹Department of Environmental Health, School of Public Health, Fudan University, Shanghai, China; ²Epidemiology Branch, National Institute of Environmental Health Sciences, National Institutes of Health, U.S. Department of Health and Human Services, Research Triangle Park, North Carolina, USA; ³Shanghai Environmental Monitoring Center, Shanghai, China; ⁴Shanghai Municipal Center of Disease Control and Prevention, Shanghai, China; ⁵Department of Health Statistics, School of Public Health, Fudan University, Shanghai, China

Abstract
Background: Various factors can modify the health effects of outdoor air pollution. Prior findings about modifiers are inconsistent, and most of these studies were conducted in developed countries.

Objectives: We conducted a time-series analysis to examine the modifying effect of season, sex, age, and education on the association between outdoor air pollutants [particulate matter < 10 µm in aerodynamic diameter (PM₁₀) , sulfur dioxide, nitrogen dioxide, and ozone] and daily mortality in Shanghai, China, using 4 years of daily data (2001–2004) .

Methods: Using a natural spline model to analyze the data, we examined effects of air pollution for the warm season (April–September) and cool season (October–March) separately. For total mortality, we examined the association stratified by sex and age. Stratified analysis by educational attainment was conducted for total, cardiovascular, and respiratory mortality.

Results: Outdoor air pollution was associated with mortality from all causes and from cardiorespiratory diseases in Shanghai. An increase of 10 µg/m³ in a 2-day average concentration of PM₁₀, SO₂, NO₂, and O₃ corresponds to increases in all-cause mortality of 0.25% [95% confidence interval (CI) , 0.14–0.37) , 0.95% (95% CI, 0.62–1.28) , 0.97% (95% CI, 0.66–1.27) , and 0.31% (95% CI, 0.04–0.58) , respectively. The effects of air pollutants were more evident in the cool season than in the warm season, and females and the elderly were more vulnerable to outdoor air pollution. Effects of air pollution were generally greater in residents with low educational attainment (illiterate or primary school) compared with those with high educational attainment (middle school or above) .

Conclusions: Season, sex, age, and education may modify the health effects of outdoor air pollution in Shanghai. These findings provide new information about the effects of modifiers on the relationship between daily mortality and air pollution in developing countries and may have implications for local environmental and social policies.

Key words: air pollution, modifiers, mortality, time-series studies. Environ Health Perspect 116:1183–1188 (2008) . doi:10.1289/ehp.10851 available via http://dx.doi.org/ [Online 9 July 2008]

Address correspondence to H. Kan, Department of Environmental Health, School of Public Health, Fudan University, Shanghai 200032, China. Telephone: 86 21 64046351. Fax: 86 21 64046351. E-mail: haidongkan@gmail.com

This study was funded by the Health Effects Institute through grant 4717-RFIQ03-3/04-13. The research was also supported by the Division of Intramural Research, National Institute of Environmental Health Sciences, National Institutes of Health, U.S. Department of Health and Human Services.

The views expressed in this article are those of the authors and do not necessarily reflect the views of the Health Effects Institute or its sponsors.

The authors declare they have no competing financial interests.

Received 5 September 2007 ; accepted 26 June 2008.