Health Benefits Attributable to Decreased Short-Term Sulfur Dioxide Exposure under Clean Air Actions in China: Evidence beyond Fine Particulate Matter

Ambient sulfur dioxide (SO2) is a critical gaseous air pollutant primarily emitted from fossil fuel combustion. Compared with fine particulate matter (PM2.5), the acute health impact of SO2 remained inadequately characterized. This study aimed to evaluate cause-specific morbidity risks and burdens associated with SO2 after accounting for the impact of PM2.5, and quantify the health benefits associated with decreased SO2 concentrations after the implementation of the Air Pollution Prevention and Control Action Plan (APPCAP) in China. We conducted a time-stratified case-crossover study including 12 major cause-specific hospital admissions in 292 cities of prefecture-level or above in China during 2013–2017. Using a two-stage statistical analytical strategy, we evaluated the city-specific associations with a two-pollutant conditional logistic regression model in the first stage and pooled the overall associations with a random-effects model in the second stage. We further estimated the reductions in attributable fractions of hospital admissions associated with decreased SO2 concentrations over the study period at both nationwide and provincial levels to explore geographical disparities. During the study period, 49,495,835 hospital admissions for respiratory, cardiovascular, mental and neurological, and kidney diseases were recorded. Short-term exposure to SO2 was associated with increased cause-specific hospital admission risks after controlling for PM2.5, with percent changes in hospital admission risks associated with each 10 μg/m3 increase in SO2 ranging from 2.53% for asthma to 5.83% for chronic kidney disease (CKD). During the implementation of APPCAP (2013–2017), the annual SO2 concentration decreased by 44.6%, and the average annual attributable fraction of major cause-specific hospital admissions was reduced by 48.3%. Notable regional disparities existed in the magnitudes of decreases in SO2 concentrations, with provincial-level administrative regions with larger decreases in SO2 concentrations experiencing greater health benefits. Our study highlights the robust morbidity risks associated with SO2 after adjustment for PM2.5 and suggests substantial health benefits linked to decreases in SO2 concentrations in China after the implementation of APPCAP. The substantial health benefits and notable regional disparities highlight the necessity for nationwide and region-specific SO2 control strategies to reduce SO2-associated health risks and burdens.