| Rapid increase rates of urbanization and industrial development in China have exacerbated air pollution.Ambient exposure to particulate matter air pollution is known to have adverse effect on public health worldwide.In recent years,the content of air pollution particles in China has increased significantly,and haze weather occurs frequently,but the sources of particles are complex,and the regional differences are also obvious.The air pollution is closely related to meteorological conditions and anthropogenic emissions.At the same time,the variations of particulate matter concentration in the atmosphere have significant impacts on surface solar radiation,which includes global radiation,direct radiation and scattered radiation.Therefore,based on the ground observational data and numerical model,this paper comprehensively analyzes the spatiotemporal variations of atmospheric particle concentrations in typical cities and regions and their impacts on the surface solar radiation.Firstly,this study proposes the temporal and spatial distribution of particulate matter（PM）in the national,regional and local scales in China during 2014-2016.The dataset of Air Quality Index（AQI）,PM10 and PM2.5 were collected in 169,369,and 367 cities in 2014,2015,and 2016 over China,respectively.Furthermore,based on the wind speed,wind direction and visibility data,the relationships between the PM2.5 concentration rising rate and the meteorological parameters as well as the weather phenomenon are discussed in the 11 typical cities.In addition,considering the influence of PM on the variations in surface solar radiation（SSR）,this paper analyzes the impact of PM on SSR based on models and the data observed in Nanjing from 2016 to 2017.The main findings are as follows:（1）During the study period,the air quality has been generally improved in the national scale but become deteriorated in some local-scale or area such as the Feiwei Plain.The northwest China（NW）and Beijing-Tianjin-Hebei regions are the worst areas of PM pollution,which are mainly manifested by the excessive PM10 caused by blowing dust in spring in NW and the intensive emissions of PM2.5 in winter in BTH.There are remarkable regional differences of particle size in China,e.g.fine PM dominant in the southern areas of Qinling Mountains-Huaihe River,but coarse mode(PM2.5-10)principal in the arid and semi-arid areas of NW with sparse vegetation coverage.With the classified seven geographic regions,we demonstrate significant spatial difference and seasonal variation of PM2.5,PM10 and PM2.5/PM10 ratio,which indicate different emission sources.（2）Based on the physical model of linear growth of fine particles,the PM2.5 pollution process in 11 big cities has been analyzed.The results show that the PM2.5 concentration rising rate has a significant correlation with the background atmospheric PM2.5 concentration.The occurrence of the PM2.5 pollution processes is usually accompanied by a decrease in wind speed.The regression slope between PM2.5 concentration rising rate and wind speed indicates whether the city is sensitive to the regional PM2.5 transport or local dispersion.The higher the slope,the more vulnerable it is to the regional PM2.5 transport and the less susceptible it is to the local diffusion.In the city with a large slope,the increase of wind speed cannot diffuse the pollutants.Instead,in the case of a large wind speed,the pollutants in the upwind areas are transported to the city.The results indicate that there is a strongly negative exponential correlation between the PM2.5 concentration rising rate and visibility.The empirical relationship between PM2.5concentration rising rate and visibility takes into account the effects of both PM2.5concentrations and meteorological parameters on visibility.（3）The results show that the increase of PM concentration will reduce the global radiation on the earth’s surface,reduce the proportion of direct radiation,and correspondingly increase the proportion of scattered radiation.Diffuse fraction,AQI,PM10,and PM2.5show negative correlations with visibility.Thus,scattered radiation and air pollution are highly related to the visibility range.Based on this relationship,the observational visibility is input into the radiative transfer model to simulate the surface solar radiation on three cloud free days with different pollution levels,and it shows that this method simulates surface solar radiation well.Compared with the coarse particles,the fine particles play an important role in the surface solar radiation.Based on this observational phenomenon,the optical characteristics of particles with different sizes are simulated by using the optical properties of aerosols and clouds model,and it is explained that this phenomenon is caused by the difference of single scattering albedo and phase function of particles with different sizes. |
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