Systematic review of synergistic effect between air pollutants and temperature on human mortality in China

Background Air pollutants and extreme temperature both pose significant threats to human health, but the synergistic effect between air pollutants and temperature on health is inconsistent.

Objective To explore a potential synergistic effect between air pollutants and temperature on the mortality in China through literature review.

Methods Wanfang Data Knowledge Service Platform, China National Knowledge Infrastructure, VIP Information Chinese Journal Service Platform, PubMed, Web of Science, Science Direct, and Embase databases were searched. "Temperature" "air pollution" "mortality" were selected as keywords to collect literature on synergistic effect between air pollutants and temperature on mortality in China. Literature was published from 2000-01-01 to 2022-07-31 in Chinese or English. Two researchers screened the literature independently according to the inclusion criteria, and the results were integrated and analyzed after data extraction. The "meta" package of R software was used for meta-analysis.

Results Twenty-seven studies met the inclusion criteria and associated air pollutants included PM₁₀, PM_2.5, O₃, SO₂, NO₂, and CO. The impact of PM₁₀ and PM_2.5 on mortality in high temperature days was higher than that in moderate temperature days. In high temperature days, a 10 μg·m⁻³ increment in PM₁₀ concentration corresponded to pooled estimates of 2.30% (95%CI: 1.34%-3.26%), 1.23% (95%CI: 0.64%-1.82%), and 1.42% (95%CI: 0.63%-2.22%) increase in non-accidental, cardiovascular, and respiratory mortalities, respectively. A 10 μg·m⁻³ increment in PM_2.5 concentration corresponded to pooled estimates of 2.56% (95%CI: 2.00%-3.13%), 2.37% (95%CI: 1.64%-3.12%), and 2.14% (95%CI: 1.03%-3.25%) increase in non-accidental, cardiovascular, and respiratory mortalities, respectively. The synergistic effect of SO₂ and NO₂ on cardiovascular and respiratory mortalities in low temperature days was higher than that in moderate temperature days.

Conclusion The synergistic effects of air pollutants and temperature on mortality in low temperature days or in high temperature days are higher than that in moderate temperature days. The health protection related to these pollutants should be strengthened in these days.