Season and temperature modify the short-term effect of nitrogen dioxide on cardiovascular mortality: a time-series study

Global climate change has increased concerns about the interactive effects of temperature and air pollution on human health. The aim of this study was to examine the effect of changes in season and temperature on cardiovascular mortality associated with nitrogen dioxide (NO2) air pollution. We obtained daily data about deaths between 2013 and 2017 from the Shenzhen Center for Disease Control and Prevention. The Meteorological Service Center and state-controlled monitoring stations in Shenzhen provided daily air temperature and NO2 air pollution data, respectively. We used two approaches to examine these modifications. First, we explored seasonal effects using distributed lag linear models (DLMs) to allow cumulative lag effects. Second, we examined variations in the effects by strata defined by the air temperature and different lag for air pollutants in assessing their interactions. We further investigated whether people aged 65 years or older were more affected by synergistic effects, because China has a high proportion of older people in the population ageing. In the cold season (November–April), the percentage increase in death for each 10 μg/m3 increment in NO2 concentration on cardiovascular mortality was associated with a 4·45% (95% CI 2·71–6·21) increase in mortality for lag0–2 (a cumulative effect over a 2-day lag) and 4·87% (2·73–7·05) increase in mortality for lag0–6 (a cumulative effect over a 6-day lag). However, there were no significant effects observed in the warm season (May–October). The NO2 effect was significantly stronger on low-temperature days (0–50th percentile) than on high-temperature days. Additionally, low air temperature made older people (aged ≥65 years) and men more susceptible to NO2 pollution. Season and temperature strongly modified the adverse effects of NO2: in the cold season and on days with low temperatures, the adverse effect of NO2 on cardiovascular mortality was significantly enhanced. These findings suggest that an increase in the number of low temperature days as a result of global climate change might alter the health effects of air pollution. National Natural Science Foundation of China (81573262).