Study On The Spatiotemporal Changes Of The Concentration Of Air Pollutants And The Air Quality Health Index In China

In the past few decades,with the rapid development of the economy and the progress of urbanization,the air pollution in China has become more serious and attracted more attention in the public.Recent studies have shown that air pollution can cause harm on human health.In order to improve the air quality in China,the Chinese government promulgated a series of standards and implemented several National Clean Air Plans（CAP）to protect the public’s health.In order to make a better evaluation of the health effect of air pollution,this paper makes a comparison of three air quality index（HAQI:Health-based Air Quality Index,AAQI:Aggregate AQI and AQI）firstly.The result shows that the HAQI is more suitable for evaluating the impact of atmospheric compound pollution on human health.Furthermore,the HAQI was applied to the study of the national health risk exposure and the relationship with socio-economic factors,which has made a comprehensive assessment of the changes in the concentration of air pollutants and the corresponding changes in health effects during the implementation of the CAP from 2015 to 2018.The result shows that during the implementation of the CAP,the concentration of particulate matter has dropped significantly,the ozone（Ozone,O₃）pollution has become prominent problem,and the health risks of pollutants in the North China Plain（NCP）are still high.In addition,changes in pollutant concentration and health effects are not only affected by emission reduction measures,but also by changes in meteorological conditions.Therefore,in order to quantify the contribution of emission reduction measures and meteorological conditions,the“Coronavirus 2019”（COVID-19）restriction period was treated as a short-term window and the precursor NO₂ that participates in the O₃ generation reaction was selected as the research object to quantify the contribution of emission reduction measures and meteorological conditions.The result shows that compared with the same period in 2019,the national health risk of pollutants during the“COVID-19”period was significantly decreased.During the“COVID-19”period,the average NO₂ emission reduction ratio of 367 cities was 37.9%,and the increment ratio caused by meteorological condition was 7.8%.In this paper,the air quality health index algorithm and the air quality data(PM_2.5,PM₁₀,SO₂,NO₂,O₃,and CO)of 367 cities across the country are mainly used to quantify changes in pollutant concentration and related health effects;Socio-economic factor data（urban built-up area,total urban population,Gross Domestic Product（GDP）,population density,share of secondary industry,share of tertiary industry,and per capita disposable income）were mainly used to explore the relationship with HAQI in each city of the country.The surface meteorological data（temperature,humidity,precipitation,wind speed,wind direction and air pressure）of 367 cities were mainly used as variables for machine learning method,which was used to predict changes in NO₂ concentration during the“COVID-19”period;Copernicus Atmosphere Monitoring Service（CAMS）reanalysis data（CAMS NO₂ and O₃）were mainly used to compare with observation data（NO₂ and O₃）to quantify the impact of anthropogenic emission change on the varying NO₂ during the“COVID-19”period.The detailed results are as follows:The study of the three air quality indexes takes Henan Province,the most populous province,as an example,and compares the HAQI,AAQI and the current AQI.The results show that the three air quality indexes mismatched each other when assessing the health effects of air pollutants.And the values of the two multi-pollutant indexes HAQI and AAQI are both larger than the single pollutant index AQI,indicating that the current AQI system may greatly underestimate the health risk of air pollution.Consequently,the multi-pollutant index HAQI that considers the pollutant exposure response relationship is more suitable for evaluating air quality health risks.The research on national population HAQI exposure and its relationship with socioeconomic factors found that the concentration is decreased by 22.1%,13.5%,46.4%and21.5%for PM_2.5,PM₁₀,SO₂ and CO,respectively.NO₂ didn’t reduced significantly（6.3%）and the concentration of O₃ increased significantly（13.7%）from 2015 to 2018.The control of O₃pollution has become the main task for the next stage of the CAP.When selecting the multi-pollutant health index HAQI to evaluate the national health risk exposure in 2018,it was found that the excess risk（ER）based on the Chinese Ambient Air Quality Standard（CAAQS）was 2times higher than the ER based on the World Health Organization（WHO）standard,indicating that the current CAAQS needs to be adjusted to better protect the public’s health.When exploring the relationship between the socio-economic factors and HAQI across the country,it was found that there is a linear relationship between HAQI and the share of the secondary industry,indicating that the secondary industry that consumes fossil fuel combustion and other energy is the main socioeconomic driver of HAQI.This result shows that the structural adjustment and upgrading of the secondary industry is an effective strategy to reduce the health risks of air pollution in China.When assessing the air pollutant related health risks and impact of the variation of the anthropogenic emissions and meteorological factors on changes in NO₂ concentration during the“COVID-19”,since the emission inventory of the CAMS model remains unchanged,the difference between CAMS NO₂ and the observation NO₂ can be regarded as anthropogenic emission reductions.The calculation results show that during the average CNY period from2015 to 2019,the national NO₂ concentration level decreased by 26.7%,and the average O₃concentration level increased by 23.3%.During the“Total COVID”period,almost all cities across the country had a certain reduction of NO₂.The average emission reduction ratio was53.57%,and the increase percentage of O₃ was 33.5%.Excluding the impact of CAP,the national average NO₂ emission reduction rate was 37.9%,and the O₃increase rate during this period was 28.6%.The machine learning results using the meteorological factors during the“COVID-19”period in 2020 and the average meteorological factors during the same period from 2015 to 2019 respectively showed that the average increment ratio of NO₂ in 367 cities across the country was 7.8%due to changes in meteorological factors.Overall,（1）When air pollution occurs,it is better to use HAQI,rather than AQI,as the guidance of human health protection;（2）After implementing the CAP of the Chinese government,the reduction of particulate matter is obvious,but the O₃ pollution problem has attracting more attention.It is necessary to adjust the structure of the secondary industry and formulate scientific emission reduction measures to reduce O₃ pollution and national health risks;（3）Compared with the same period in 2019,the national health risk of pollutants during the“COVID-19”period was significantly decreased.The use of CAMS reanalysis data and machine learning methods to quantify the impact of emissions and meteorology variation on the changes in pollutant concentrations also provides a scientific basis to better formulate emission reduction strategies.