Size-Specific Particulate Air Pollution And Hospitalization For Cardiovascular Diseases: A Case-Crossover Study In Shenzhen, China

Background: Despite contributing to the majority of ambient fine particles (PM2.5), PM1 (particulate matter [PM] with aerodynamic diameter <= mu m) remains poorly studied in terms of its acute effects on cardiovascular dis-eases (CVDs) in China. This study aims to evaluate the short-term associations of size-specific PMs (i.e., PM1, PM2.5, and PM10) exposures with hospital admissions for CVDs in a southern Chinese metropolis.Methods: We collected 5,969 records of hospital admissions for CVDs and daily average concentrations of air pollutants and weather conditions in Shenzhen from January 1st 2015 to December 31st 2017. We adopted a time-stratified case-crossover design and conditional logistic regression models to assess short-term associations between size-specific PMs and CVD hospitalizations along different exposure days.Results: During the study period, annual average concentrations of PM1, PM2.5, and PM10 were 18.7, 27.8, and 45.4 mu g/m(3), respectively. Compared to PM2.5 and PM10, PM1 exhibited a generally stronger association with CVD hospitalizations. Hospital admissions for CVDs increased by 6.7% (95% confidence interval: 1.2-12.5%), 4.5% (0.4-8.7%), and 3.4% (0.5-6.3%), corresponding to per 10-mu g/m(3) rise in exposure to PM1, PM2.5, and PM10 at lag 03 days. In our stratified analyses by CVD sub-causes, size-specific PMs showed consistent effects on hypertension but no evident association with ischemic heart disease (IHD) and stroke. Seasonal analysis revealed significantly larger PM-associated risks among IHD patients in cold months (October-March). Nevertheless, in warm months (April-September), the older group (aged 65+ years) was more prone to adverse effects of PM1 exposure at lag 0 day.Conclusion: Short-term exposure to size-specific PMs, PM1 in particular, may trigger incidences of CVD hospitalization. To effectively mitigate adverse effects of particulate pollution, evidence-based PM1 standards should be developed as well in Chinese less-polluted megacities.