Health Risk of Increased O3 Concentration Based on Regional Emission Characteristics under the Unusual State of the COVID-19 Pandemic

Photochemical oxidant concentration increases with the decrease in nitrogen oxide (NOx) concentration in volatile organic compound (VOC)-sensitive areas with several automobiles and factories. We aimed to quantify the changes in health risks from ozone (O3) and nitrogen dioxide (NO2) using disability-adjusted life years (DALY) in Osaka City, which is one of the major cities in Japan. ADMER-PRO version 1.0, an atmospheric model for secondary products, was used to estimate the concentration distribution of NO2, VOC, and O3 using the year-on-year change of traffic during the declaration of the state of emergency in response to the coronavirus disease 2019 (7 April to 21 May 2020). NO2 concentration decreased by an average of 0.962 ppb in 88.9% of the grids in Osaka City, whereas O3 concentration increased by an average of 1.00 ppb in all the grids with a 26–28% reduction of traffic volume due to the pandemic. We also found three intensities for the VOC-sensitive condition depending on the different regional emission characteristics, with the DALYs of health risks from the decrease in NO2 exceeding those from the increase in O3, reaching 811.4 and 55.90 total DALYs in the city, respectively.