Multi-time-scale surface ozone exposure and associated premature mortalities over Indian cities in different climatological sub-regions

Abstract

Surface ozone (O₃) pollution driven by natural and anthropogenic emissions is one of the serious and potentially life-threatening issues in India, owing to associated human mortality. This study analyses the O₃ health metric and their long and short-term health effects (i.e. respiratory, cardiovascular (CVD) and all-cause) in 76 Indian cities. Firstly, the maximum daily 8-hour average (MD8A) is characterized by annual, seasonal, monthly, weekly and diurnal scales from 2020 to 2022. High ozone levels continue to be a concern in the Central, Northern, Western, and Eastern sub-regions, as over 60% of cities here exceed the WHO baseline (70 µg m^− 3). On average, 15% of cities in Northern, Western and Central sub-regions surpass WHO grade (100 µg m^− 3). While overall ozone concentrations decreased from 2020 to 2021, the median concentration increased in 2022. Peak ozone levels for the Northern, Western, and Central sub-regions occur between April and May, while Southern India has a monthly variation that is relatively stable. The weekdays have lower ozone levels than the weekends, with the summer weekends showing noticeable difference. Further, the long and short-term surface ozone exposure is associated with a total of 13,222 and 1944 premature mortalities respectively, showing a rise of 40%, 50% and 54% in 2022 for all-cause, respiratory and CVD mortalities respectively from 2020 levels. With a possible rise in precursor emissions and heat-wave events in the near future, a potential rise in health effects associated with O₃ exposure could be expected over the Indian region.