Abstract
BackgroundAmbient ozone (O3) concentration has been reported to be significantly associated with mortality. However, linearity of the relationships and the presence of a threshold has been controversial.ObjectivesThe aim of the present study was to examine the concentration-response relationship and threshold of the association between ambient O3 concentration and non-accidental mortality in 13 Japanese and Korean cities from 2000 to 2009.MethodsWe selected Japanese and Korean cities which have population of over 1 million. We constructed Poisson regression models adjusting daily mean temperature, daily mean PM10, humidity, time trend, season, year, day of the week, holidays and yearly population. The association between O3 concentration and mortality was examined using linear, spline and linear-threshold models. The thresholds were estimated for each city, by constructing linear-threshold models. We also examined the city-combined association using a generalized additive mixed model.ResultsThe mean O3 concentration did not differ greatly between Korea and Japan, which were 26.2 ppb and 24.2 ppb, respectively. Seven out of 13 cities showed better fits for the spline model compared with the linear model, supporting a non-linear relationships between O3 concentration and mortality. All of the 7 cities showed J or U shaped associations suggesting the existence of thresholds. The range of city-specific thresholds was from 11 to 34 ppb. The city-combined analysis also showed a non-linear association with a threshold around 30-40 ppb.ConclusionWe have observed non-linear concentration-response relationship with thresholds between daily mean ambient O3 concentration and daily number of non-accidental death in Japanese and Korean cities.
Highlights
Ozone (O3), a component of the troposphere, is formed by photochemical reaction between precursor chemicals, such as volatile organic carbon (VOC) and oxides of nitrogen (NOx), which are emitted from both anthropogenic and natural sources
Non-Linearity of Ozone Effect on Mortality model compared with the linear model, supporting a non-linear relationships between O3 concentration and mortality
We have observed non-linear concentration-response relationship with thresholds between daily mean ambient O3 concentration and daily number of non-accidental death in Japanese and Korean cities
Summary
Ozone (O3), a component of the troposphere, is formed by photochemical reaction between precursor chemicals, such as volatile organic carbon (VOC) and oxides of nitrogen (NOx), which are emitted from both anthropogenic and natural sources. The O3 has existed in the troposphere at the level of background concentration (20–45 ppb) due to the natural sources of precursor chemicals. Exposure to ambient O3 has been reported to exacerbate respiratory diseases and increase the risk of death [3,4,5,6]. The exposure to ambient O3 causes inflammation and oxidative stress in lungs, the putative mechanism of increased risk of cardiovascular morbidity and mortality [7,8,9,10]. Ambient ozone (O3) concentration has been reported to be significantly associated with mortality. Linearity of the relationships and the presence of a threshold has been controversial
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