[Meteorological Impact Assessment of PM2.5 and O3 Complex Pollution in Key Regions of China Based on Meteorological Conditions Index].

Meteorological conditions play a key role in the occurrence and evolution of atmospheric complex pollution. Considering the different pollution formation mechanisms of PM2.5 and O3, statistical calculation and in-depth learning methods were used to construct the PM2.5 and O3 meteorological condition indexes based on long-term pollution meteorological observation data. A research method was developed to study the meteorological characteristics and impact contribution of atmospheric complex pollution by using the meteorological condition index, and quantitative analysis of the distribution and variation of pollution excluding the influence of regional meteorological differences was also conducted. The results showed that in the summer of 2021, the pollution meteorological conditions in the key regions in central and eastern China were generally worse in the north and better in the south(index:"2+26" cities>the border area of Jiangsu, Anhui, Shandong, and Henan>the Yangtze River Delta) and the worst in June and the best in July. The "double high" pollution began to appear when the PM2.5 meteorological condition index>30 and O3 meteorological condition index>100; meanwhile, the unfavorable meteorological conditions for O3 also promoted the increase in PM2.5 concentration, resulting in the frequency of "double high" increases with the increase in O3 meteorological condition index. Compared with that during the same period last year, ρ(PM2.5) of each region decreased by 3.9 µg·m-3, 3.3 µg·m-3, and 1.4 µg·m-3 due to the contribution of the improvement in the pollution meteorological conditions, which is nearly 58.5% on average of the total decrease in PM2.5 concentration. However, the change in O3 pollution meteorological conditions was better in the north and worse in the south, and the overall deterioration in the Yangtze River Delta Region led to approximately 2.8 µg·m-3 growth for the O3 concentration. The PM2.5 and O3 concentrations after excluding the impact of meteorological differences showed different distribution characteristics from the air quality monitoring, in which the high concentrations of PM2.5 were distributed along the Bohai Sea, the inter-provincial border, and the south of the region, whereas the high concentrations of O3 were concentrated along the Taihang Mountains, around Mount Tai, and in parts of the Yangtze River Delta. The daily concentration variations in a single city during a specific pollution control period could be used as a basis for evaluating the effectiveness of local supervision and control, which will provide a reference for the dynamic supervision and daily scheduling of local control management.

[Analysis of Characteristics and Causes of a Typical Haze Pollution in Beijing in the Winter of 2019].

In order to study the pollution characteristics and causes of winter haze pollution in Beijing, a typical PM2.5 pollution process in Beijing in December 2019 was used as the analysis object using aerosol vertical detection data, boundary layer meteorological field and near-ground turbulence data, and the difference in haze. The characteristics of the pollution stage and the evolution of the physical and chemical characteristics of the boundary layer were comprehensively analyzed. The results showed that ① the pollution process in Beijing during the observation period lasted 5 d and experienced two generations and eliminations. The maximum hourly PM2.5 concentration was 220 µg·m-3 and the time exceeding the severe pollution standard was 64 h, thereby accounting for 53% of the total time. ② The aerosol optical properties and meteorological field observation data showed that the pollution originated from the regional transmission of aerosols and water vapor on the surface of the southwest urban agglomeration in Beijing, which accounted for 48% of the total pollution transmission, followed by a stable high-altitude situation and ground pressure field configuration. The near-surface layer maintained weak southerly winds (wind speed: 1-2 m·s-1), a strong inversion temperature close to the ground ï¼»0.8 K·(100 m)-1ï¼½, high humidity (relative humidity above 80%), and other unfavorable diffusion weather conditions, thereby promoting the accumulation of pollutants and the conversion of moisture absorption. Superimposing local pollution emissions were the main reasons for the maintenance of haze days. In addition, the near-ground extinction coefficient increased from 0.070 km-1 to 5.954 km-1, and the depolarization ratio decreased from 0.05 to 0.02 during the two pollution generation and disappearance processes, thereby indicating that the spherical characteristics of aerosols gradually became significant as the pollution increased. ③ The analysis of the turbulence observation data showed that the characteristic quantities of different pollution stages were significantly different and negatively correlated with the pollutant concentration. Before the occurrence of heavy pollution, the turbulence statistics (turbulence intensity, friction velocity, and turbulent kinetic energy) suddenly decreased from high values (the hourly variation rate was 77%, thereby far exceeding the daily fluctuation of 33%), and the turbulence intensity responded first. During the pollution accumulation stage, the friction velocity (0.04-0.21 m·s-1), turbulence intensity (average: 0.678 m2·s-2), and turbulence energy (average: 0.643 m2·s-2) were maintained at a low level, and the bottom atmosphere had a poor mixing and diffusion ability, which is important for continuous pollution accumulation. Four hours before the end of the pollution event, the turbulence intensity again showed a sharp increase (increment of more than one order of magnitude); thus, the turbulence intensity can be used as a predictive indicator of the occurrence and end of a heavy pollution event, and the response time is the same as the continuous turbulence intensity after the turbulence peak. In addition, the sensible heat fluxes on sunny days and haze days were both transported from the ground to the atmosphere, and showed clear daily single-peak changes. The sensible heat flux on haze days (20 W·m-2) was smaller than that on sunny days (60 W·m-2). The latent heat flux was approximately 0 W·m-2 in the whole process. ④ There was a feedback effect between the meteorological conditions of the pollution layer and the boundary layer. On the one hand, unfavorable diffusion of the meteorological conditions was conducive to the accumulation of pollution. On the other hand, the aerosol layer and water vapor cooling effect that accumulated near the ground were worse than the night cooling radiation on the inversion layer The contribution was greater, thereby further inhibiting the development of turbulent motion and ultimately resulting in increased pollution.

[Numerical Study on the Characteristics of Regional Transport of PM2.5 in Shandong Province During Spring in 2014].

In this paper, spatial and temporal distribution, transportation and deposition of PM2.5 in Shandong Province in Spring, 2014 were all analyzed by applying PSAT of CAMx model and we also developed a transport matrix of PM2.5 between different cities in Shandong. The results showed that ρ(PM2.5) presented obvious spatial distribution characteristics; ρ(PM2.5) was higher in the western part compared to that in peninsula and ρ(PM2.5) was mainly concentrated below 2 000 m in vertical direction. Simulated horizontal transport flux of PM2.5 was up to 110 µg.(m2.s)-1 and the total deposition amount of PM2.5 was 23. 05 x 10(4) t in Shandong during Spring, 2014. Analysis of regional contribution found that the pollutants mainly came from local districts and the average external transport contribution to the whole Shandong province was about 21. 08% ± 3. 83% while it was 40. 45% ± 5. 96% between different cities; the contribution rates of Jinjinji distrcit, background and boundary conditions gradually increased by 7. 56% and 6. 18% respectively as the altitude increased.