Premature mortality in Japan due to ozone

•Premature mortality cases in Japan were estimated using modeled and monitored ozone.•Modeled ozone in 2005 in Japan caused 13,000 (95% CI: 4320-17,300) premature mortality cases.•Monitored ozone in 2005 in Japan caused 5220 (95% CI: 1740-6960) premature mortality cases.•Modeled ozone caused about 2.5 times greater premature mortality cases compare to monitored ozone.•Premature mortality estimation using monitored ozone from 1145 monitors in Japan is less uncertain than that of modeled ozone.

In Japan, all 47 prefectures conduct routine air quality monitoring at 1145 stations throughout the country to assess environmental effects. This study aims to provide a better understanding of possible estimations of premature mortality in Japan caused by exposure to monitored and modeled concentrations of tropospheric ozone during the period from January to December, 2005. The spatial distribution and temporal variation of ozone concentrations were modeled using the Models-3 Community Multiscale Air Quality modeling system coupled with the Regional Emission Inventory in Asia (CMAQ/REAS). Premature mortality caused by exposure to ozone was calculated assuming a relative risk (RR) value of 1.003 [95% Confidence Interval (CI): 1.001-1.004] for concentrations above 35 ppb according to the SOMO35 index (annual Sum of daily maximum 8-h Ozone Means Over 35 ppb) recommended by WHO (2008). Based on CMAQ/REAS simulations, the estimated all-cause premature mortality in 2005 is about 13,000 (95% CI: 4320-17,300) cases. This value is 2.5 times greater than the estimated premature mortality based on monitored ozone concentrations, which is 5220 (95% CI: 1740-6960) cases.