Ambient Nitrogen Dioxide and Hospitalizations of Full-Spectrum Respiratory Diseases: A National Case-Crossover Study

Few multicity studies have examined the acute effects of nitrogen dioxide (NO₂) on respiratory disease (RD), especially its specific causes. This study aimed to investigate the associations between short-term exposure to NO₂ and hospitalization of full-spectrum RDs in China. Hospitalization of 10 major categories and 40 cause-specific RDs were obtained from 20 provinces over the study period of 2013-2020. A time-stratified case-crossover study was conducted at the individual level to explore the associations between NO₂ and RDs. NO₂ was significantly associated with increased hospitalization of eight major RDs (acute upper respiratory infections, influenza and pneumonia, acute lower respiratory infections, upper respiratory tract diseases, chronic lower respiratory diseases, respiratory interstitium diseases, pleura diseases, and other respiratory diseases) and 18 specific causes of RDs, with the largest associations observed on lag 0-1 day. The effect estimates ranged from 0.75 to 4.09% per 10 μg/m³ of NO₂ exposure. The associations remained robust after controlling for copollutants. The concentration-response curves were mostly positive and linear. This nationwide study provides comprehensive information on the acute effects of NO₂ on respiratory morbidity across the full spectrum, highlighting the need for caution with regard to this important traffic-related air pollutant in current pollution control programs.