Ozone Modifies Associations between Temperature and Cardiovascular Mortality – analysis of the NMMAPS data

Cizao Ren ^1*, Gail M Williams ², Lidia Morawska ³, Kerrie Mengersen ⁴ and Shilu Tong ¹

¹ School of Public Health, IHBI, Queensland University of Technology, Australia
² School of Population Health, University of Queensland, Australia
³ School of Chemical and Physical Sceinces, Queensland University of Technology, Australia
⁴ School of Mathematical Sciences, Queensland University of Technology, Australia

^* To whom correspondence should be addressed. E-mail: rencizao{at}yahoo.com.

Accepted 14 September 2007

Abstract

Objectives: Both ambient ozone and temperature are associated with human health. However, few data are available on whether ozone modifies temperature effects.. This study aims to explore whether ozone modified associations between maximum temperature and cardiovascular mortality in the United States. Methods: We obtained data from the US National Morbidity, Mortality, and Air Pollution Study (NMMAPS) website. We used two time-series Poisson regression models (a response surface model and a stratification model) to examine whether ozone modified associations between maximum temperature and cardiovascular mortality (CVM) in 95 large US communities during 1987-2000 in summer (June to September). We used Bayesian meta-analysis to pool estimates in each community. Results: The response surface model was used to examine the joint effects of temperature and ozone on CVM in summer. Results indicate that ozone positively modified the temperature-CVM associations across the different regions. The stratification model quantified the temperature-CVM associations across different levels of ozone. Results show that in general the higher the ozone concentration, the stronger the temperature-CVM associations across the communities. A10°C increase in temperature on the same day was associated with an increase in CVM by 1.17 % and 8.31% for the lowest and highest level of ozone concentrations in all communities, respectively. Conclusion: Ozone modified temperature effects in the different regions in the United States. It is important to evaluate the modifying role of ozone when estimating temperature-related health impacts and to further investigate the reasons behind the regional variability and mechanism for the interaction between temperature and ozone.

Keywords: air pollution, interaction, mortality, ozone, temperature

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