Objective To explore the effect of short-term exposure to nitrogen dioxide (NO₂) on the daily mean outpatient visits for circulatory and respiratory diseases.

Methods Based on the outpatient department data of a grade A tertiary hospital in Yangzhou, China, from 2023 to 2024, as well as air pollutants and meteorological data, a generalized additive model was used to analyze the association between NO₂ concentration and outpatient visits for the two diseases. Adjusting for time trends, holidays, day-of-the-week effects, and meteorological factors, the lag effect and two-pollutant confounding effect were investigated. A stratified analysis was conducted for sensitive populations, and exposure-response curves were plotted.

Results During the study period, the median daily outpatient visits for circulatory and respiratory diseases in the hospital were 459 and 595, respectively, and the mean daily exposure level of NO₂ was 30 μg/m³. The single-day lag analysis showed that the effects of NO₂ exposure at lag0 d and lag6 d were the strongest for circulatory and respiratory diseases, respectively. For every 10 μg/m³ increase in NO₂ concentration, outpatient visits for circulatory and respiratory diseases increased by 1.46% (95% confidence interval CI: 0.54%-2.38%) and 1.64% (95%CI: 0.51%-2.78%), respectively. The cumulative lag effect analysis revealed that the most significant effect was observed at lag03 d for the circulatory system disease (with an increase in outpatient visits of 2.09% 95%CI: 1.20%-2.99%) and at lag06 d for the respiratory system disease (with an increase in outpatient visits of 7.46% 95%CI: 6.02%-8.91%). After adjusting for the effects of co-pollutants such as fine particulate matter (PM_2.5), the effect of NO₂ remained robust. Regarding respiratory diseases, children and adolescents aged ≤18 years were more sensitive to NO₂ exposure, with heterogeneity across age groups observed. The exposure-response curve for circulatory diseases was non-linear, while that for respiratory diseases was nearly linear and had no pronounced threshold effect.

Conclusion Short-term exposure to NO₂ significantly increases the risk of outpatient visits for both diseases. Special attention should be paid to respiratory protection for children and adolescents under the age of 18 years, and the environmental air quality standards should be revised in a timely manner.