Increased tropospheric ozone levels as a public health issue during COVID-19 lockdown and estimation the related pulmonary diseases

The aims of this study were to i) investigate the variation of tropospheric ozone (O3) levels during the COVID-19 lockdown; ii) determine the relationships between O3 concentrations with the number of COVID-19 cases; and iii) estimate the O3-related health effects in Southwestern Iran (Khorramabad) over the time period 2019-2021. The hourly O3 data were collected from ground monitoring stations, as well as retrieved from Sentinel-5 satellite data for showing the changes in O3 levels pre, during, and after lockdown period. The concentration-response function model was applied using relative risk (RR) values and baseline incidence (BI) to assess the O3-related health effects. Compared to 2019, the annual O3 mean concentrations increased by 12.2% in 2020 and declined by 3.9% in 2021. The spatiotemporal changes showed a significant O3 increase during COVID-19 lockdown, and a negative correlation between O3 levels and the number of COVID-19 cases was found (r = -0.59, p < 0.05). In 2020, the number of hospital admissions for cardiovascular diseases increased by 4.0 per 105 cases, the mortality for respiratory diseases increased by 0.7 per 105 cases, and the long-term mortality for respiratory diseases increased by 0.9 per 105 cases. Policy decisions are now required to reduce the surface O3 concentrations and O3- related health effects in Iran.