Objective To quantitatively evaluate the impacts of atmospheric ozone exposure on outpatient visits for respiratory and circulatory diseases in Nantong.

Methods Data were collected on air pollutants, meteorological factors and outpatient visits in Nantong First People's Hospital from 2017 to 2019. A generalized linear model was used to investigate the exposure-response relationship between ozone mass concentration and outpatient visits.

Results In 2017—2019, the median(P₂₅, P₇₅) of daily maximum 8-hour mean ozone concentration(O₃-8 h) was 102(80, 134) μg/m³, with 151 days(13.78%) exceeding the recommended limit. In Nantong, O₃-8 h exposure was positively correlated with the number of outpatients for respiratory diseases during the year and in cold season, and negatively correlated with the number of outpatients for respiratory diseases, circulatory diseases and pediatric respiratory diseases in warm season. In year-round analysis, every 10 μg/m³ increase of O₃-8 h mass concentration resulted in a 1.21%(95%CI: 0.45%, 1.97%) increase in respiratory outpatient visits, while 1.15%(95%CI: 0.64%, 1.65%) and 1.25%(95%CI: 0.62%, 1.88%) decrease in outpatient visits for circulatory diseases and pediatric respiratory diseases, respectively. In cold season, the impact of ozone exposure on outpatients with respiratory diseases increased, and each 10 μg/m³ increase of O₃-8 h mass concentration resulted in a 3.02%(95%CI: 1.22%, 4.85%) increase in outpatient visits for respiratory diseases. In warm season, ozone exposure was negatively correlated with outpatient visits for all three diseases.

Conclusion There is a positive correlation between the increase of ozone mass concentration and outpatients visits with respiratory diseases. Elevated ozone levels have more pronounced acute health effects in cold season, and the sensitive population should be protected promptly.