The Impact of Ambient PM2.5 on Emergency Ambulance Dispatches Due to Circulatory System Disease Modified by Season and Temperature in Shenzhen, China

The adverse effects of short-term exposure to pollutants are the focus of many epidemiological studies. Little is known about the modification effects of season and temperature on the association between pollutants and the acute onset of circulatory diseases. The aim of this study was to investigate the effect of PM2.5 on emergency ambulance dispatches (EADs) due to circulatory system diseases in different seasons and temperature levels, and to locate the vulnerable population. We collected data on daily emergency ambulances, meteorological data, and air pollution concentration in Shenzhen from 2013 to 2020. A distributed lag nonlinear model was conducted to assess the effect of PM2.5 on circulatory system disease emergency ambulance dispatches modified by season. In addition, generalized additive models were used to detect the interactive effect of PM2.5 and temperature on emergency ambulance dispatches due to circulatory disease. A 10 mu g/m3 increase in PM2.5 concentration was associated with a 2.43% (1.47-3.40%) increase in the risk of circulatory system disease emergency ambulance dispatches over lags of 0-5 days during the cold season, compared to 0.75% (-0.25-1.76%) during the warm season. This trend was consistent across temperature levels, with a significant 2.42% (1.47-3.10%) increase on low-temperature days, while no significant effect was observed on high-temperature days. For young people, the effect of PM2.5 on circulatory system disease emergency ambulance dispatches was higher in the cold season and low temperature days. The cold season and low temperature significantly enhanced the adverse effect of PM2.5 on the acute onset of circulatory system diseases, especially in young people. It is critical to focus on the synergistic effects of temperature and pollutants on the health of different vulnerable populations in different regions and climates.