Short-term ambient particulate matter pollution of different sizes and respiratory hospital admission in the Beibu Gulf area of Southern China

•A time-stratified case-crossover design is constructed to estimate the associations.•A large-scale, high-quality, and multisite representative dataset is used.•Increased risk of respiratory hospitalizations associated with particulate matter.•Male in the warm season is more vulnerable to the impacts of particulate pollution.•7% of respiratory hospitalizations is attributable to short-term exposure of PM2.5.