Effect of changes in season and temperature on cardiovascular mortality associated with nitrogen dioxide air pollution in Shenzhen, China

The intricate association of mortality risk with ambient air pollution and temperature is of growing concern. Little is known regarding effect of changes in season and temperature on daily cardiovascular mortality associated with air pollutant nitrogen dioxide (NO2).Our study aimed to assess the effect of NO2 on cardiovascular mortality modified by season and daily air temperature in the effect, and further to identify the population highly susceptible to cardiovascular mortality associated with NO2 and air temperature.We collected daily cause-specific death data, weather conditions, and air pollutant concentrations in Shenzhen from 2013 to 2017. Distributed-lag linear models were employed to analyze the effect of season on the NO2-associated mortality. Furthermore, generalized additive models were combined with stratification parametric analysis to estimate the interaction effect of NO2 with air temperature on cardiovascular mortality.In the cold season, the percentage increase in daily mortality for every 10 μg/m3 increment in NO2 concentration over lags of 0-2 days was 4.45% (95% CI: 2.71-6.21%). However, no statistically significant effect of NO2 was observed in the warm season. Compared with high-temperature days (>median temperature), a 3.51% increase in mortality (95% CI: 2.04-5.01%) over low-temperature days (≤median temperature) for the same increase in NO2 was significant. Air temperature modified the effect of NO2 on daily mortality by 4.08% (95% CI: 2.28-5.91%) for the elderly (age ≥ 65 years) on low-temperature days vs. -0.82% (95% CI: -3.88-2.34%) on high-temperature days, and 3.38% (95% CI: 1.50-5.29%) for males on low-temperature days vs. -0.73% (95% CI: -3.83-2.47%) on high air temperature days.The cold season and low temperatures could significantly enhance the effect of NO2 on cardiovascular mortality. The elderly and males suffering from cardiovascular disease should take precautions against low temperature and NO2 air pollution.