| Climate change has become one of the greatest health threats in the 21st century,affecting human health in many ways and leading to multiple,strong,widespread and concurrent extreme weather and climate events.Frequent extreme temperature events(ETEs)are one of the stressors that receive the most attention.ETEs usually refer to a continuous period of extreme low or high temperatures,called cold spells or heat waves.The health risk and disease burden of ETEs may be not eased in the future,even if the population become more adaptable.Air pollution is another important environmental problem.It causes at least 4 million premature deaths worldwide every year,and the trend is increasing year by year,bringing huge disease burden to population.Studies have shown that their effects on health outcomes may be not independent,but the combined effects of multiple exposures.At present,studies on the interaction between cold spells,heat waves and air pollution are limited,and relevant studies often failed to fully elucidate the form,size and possible mechanism of interaction.In the future,under all greenhouse gas emission scenarios,the global mean temperature will continue to rise.People will be exposed to more frequent extreme temperature,but air quality will continue to improve.In this background,the following questions need to be answered:1)what the impact do extreme temperature and air pollution have on human health respectively;2)whether extreme temperature can alter the health effects of air pollution on population,whether the adverse impact of extreme temperature will be weakened under the condition of low concentration of air pollution.Taking Zibo City of Shandong Province as the study area,this study evaluated the shortterm impact of extreme temperature and air pollution on population mortality respectively,explored the interaction form and size preliminarily,and identified the vulnerable population.It would be helpful for policy makers to design effective coping strategies for climate change and long-term air pollution prevention and control measures,and to provide scientific reference for disease prevention and control and public health strategy formulation in the background of global climate change.Materials and Methods:Data on non-accidental death,circulatory disease death and respiratory disease death were collected from January 1,2015 to December 31,2019,as well as daily air pollutants and meteorological data,including air quality index(AQI),CO,NO2,PM10,PM2.5,O3,SO2,mean temperature and relative humidity during the same period.Cold spells were defined as a weather process in which the daily mean temperature lasted for more than 2 days below the 5th percentile of its distribution(-2.6℃)during the study period,and heat waves were defined as a weather process in which the daily mean temperature lasted for more than 4 days above the 92.5th percentile of its distribution(27.1℃)during the study period.First,descriptive analysis of the variables was performed,then distributed lag non-linear model(DLNM)was adopted to explore main and additional effects of cold spells or heat waves,and the delayed effects of air pollution.Finally,non-parametric binary response model,stratified model and joint effect model were adopted to further explore the form and size of interaction.Results:1.A total of 144,310 non-accidental death,77,821 circulatory disease death and 11,767 respiratory disease death were reported during the study period.There were 23 cold spells with a total of 81 days,and 13 heat waves with a total of 73 days,all of which showed a fluctuating upward trend.Compared with the daily average number of non-accidental death,circulatory disease death and respiratory disease death,the corresponding mean values during the cold spells increased by 23.92%,29.34%and 59.38%,respectively.During the heat waves,the corresponding mean values of the first two increased by 4.68%and 7.28%,respectively,while the respiratory disease death remained unchanged.2.ETEs significantly increased the risk of death,and heat waves contributed more to population mortality than cold spells.The lag effects of cold spells and heat waves showed different trends.The cold spells had a long lag period,and the effect values fluctuated upward trend.The effects of heat waves were relatively short-term.The adverse effects were strong within two days after exposure,and the effect values increased first and then decreased.After adjusting for the influence of daily mean temperature,the additional effects of ETEs were still significant,suggesting additional health risks existed.Cold spells had a greater impact on men and those aged≥65 years,and heat waves had a greater impact on women and those aged≥65 years,but the differences between subgroups were not statistically significant.3.AQI,O3,PM10 and PM2.5 were significantly correlated with non-accidental death,circulatory and respiratory disease death.The effects of air pollution were relatively short and showed a trend of first rising and then decreasing,while the effects of CO,NO2 and SO2 were weak and mostly not statistically significant.Women and people aged 65 years and older were more likely to be affected by air pollutants,and the differences among some subgroups were statistically significant.4.There was interaction between extreme temperature and AQI.The response curve suggested that daily mean temperature and AQI had interaction effects on population mortality.Stratified model showed that cold spells or heat waves reduced the adverse effects of AQI,and the interaction was statistically significant.The joint effect model revealed the interaction form of the two:the risk caused by ETEs and high AQI was lower than that caused by ETEs and low AQI,but higher than that caused by high AQI alone.The interactions of ETEs and AQI on non-accidental death,circulatory and respiratory disease death were not statistically significant,but in subgroup analysis,heat waves and AQI had a significant negative interaction on non-accidental death and circulatory disease death in females and those aged≥65 years.That is,the effect of heat waves and low AQI was greater than the risk of death of heat waves and high AQI.Conclusions:1.Extreme temperature and some air pollutants were significantly associated with population mortality,and females and those aged≥65 years were vulnerable groups.2.Extreme temperature changed the adverse effects of air pollution.There was negative interaction between heat waves and AQI.But low AQI did not mitigate the adverse effects of extreme temperatures,that is,the risk of death caused by low AQI and ETEs was greater than that caused by high AQI and ETEs.The risk caused by extreme temperature would continue to increase.Policy recommendations:1.Take multiple measures to strengthen the ability to prevent extreme weather risks,improve the local extreme weather forecasting and early warning systems,and add cooling equipment or summer stations and other basic public facilities.Continue to strengthen the control of air pollutants by implementing active air quality management plans and carbon reduction measures.2.Formulate coordinated management strategies for climate change and air pollution,intensify the publicity and education of relevant health knowledge and countermeasures,and pay more attention to older women.The population should focus on the cold spells or heat waves warning issued by the meteorological department in time,and be aware of those days with good air quality.They should take protective measures,such as turning on air conditioners,wearing masks and reasonably arranging outdoor activities,so as to better cope with the environmental risks and challenges in the future. |
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