What are the specific reasons for heavy pollution?

The high emission intensity of pollutants is the internal cause of the formation of heavily polluted weather, while unfavorable meteorological conditions such as static stability, small wind, high humidity and inversion temperature are the external causes of the formation of heavily polluted weather. At present, fine particulate matter (PM2.5) is the pollutant that has the greatest impact on China's atmospheric environmental quality. No matter from the number of cities exceeding the standard, the degree of exceeding the standard in each city, or the contribution to heavily polluted weather, the impact of PM2.5 is far greater than other pollutants. Atmospheric PM2.5 pollution sources mainly include the direct contribution of primary particulate matter emission and the indirect contribution of secondary transformation of gaseous precursors such as sulfur dioxide (SO2), nitrogen oxides (nitrogen oxides), volatile organic compounds (VOCs) and ammonia (NH3).

The Ministry of Environmental Protection started the source analysis of PM2.5 in 35 municipalities directly under the central government, provincial capital cities and cities with separate plans in 20 14 10. The results show that coal burning, motor vehicles, dust and industrial production are the main sources of PM2.5, and there are great regional differences in the contribution of atmospheric PM2.5 sources. The primary source of PM2.5 in Shijiazhuang, Jinan, Taiyuan, Changchun, Harbin, Nanjing, Guiyang, Urumqi and other cities is coal-fired emissions, accounting for more than 25%; The results of source analysis of cities in Hebei show that coal-fired emissions, as the primary source of PM2.5 in Baoding, Langfang and Cangzhou, account for more than 30%, and the prevention and control of coal-fired pollution is the top priority of PM2.5 pollution prevention and control in these cities. Especially in the winter heating period, the contribution of coal-fired emissions to atmospheric PM2.5 pollution in Beijing, Tianjin and Hebei and surrounding areas is more prominent. The main components of PM2.5, such as organic carbon (OC), elemental carbon (EC) and sulfate, are directly related to coal-fired emissions, and other main components, such as nitrate and ammonium salt, are also partly derived from coal-fired boilers and loose coal combustion. The primary task of preventing and controlling heavy air pollution in winter is to reduce coal-fired emissions.

But at the same time, we should also see that the primary source of PM2.5 in Beijing, Shanghai, Hangzhou and other cities is motor vehicle emissions, accounting for about 30% (Shanghai includes motor vehicles and off-road mobile sources), and the contribution of motor vehicle emissions to PM2.5 in Shenzhen is even as high as 4 1%. The primary source of PM2.5 in cities such as Dalian, Xiamen, Chongqing (the main city), Chengdu and Xi is also motor vehicle emissions, accounting for the proportion. During the early warning period of heavy pollution, Beijing and other cities have increased the control of motor vehicle pollution, especially the control of high-emission vehicles such as old cars and diesel cars, which is helpful to reduce the peak pollution. In addition, the primary source of PM2.5 in Tianjin, Hohhot, Yinchuan, Lanzhou and Xining is dust pollution, accounting for 25%~40%. These cities should further strengthen the prevention and control of dust pollution.

Environmental monitoring data and related research show that since the implementation of "Ten Atmospheric Articles" in 20 13, the prevention and control measures of air pollution in China and the whole country have achieved results, and the concentration of primary pollutants (SO2, NO2, primary particulate matter, etc.) has dropped significantly. However, the decline of secondary components in particulate matter is obviously slower than that of primary pollutants, and the explosive growth of atmospheric PM2.5 during heavy pollution is often related to the rapid growth of secondary components such as sulfate and nitrate. It is worth noting that apart from the mechanism that gaseous precursors such as SO2 and nitrogen oxides are transformed into secondary components such as sulfate and nitrate respectively, there are also interactions among these chemical components, such as NO2 accelerating the transformation of SO2 into sulfate, resulting in the air pollution generation effect of "1+ 1 >: 2". How these mechanisms play a role in the formation of heavy air pollution is very important for the prediction and early warning of heavy pollution and the formulation of multi-pollutant cooperative control scheme.

Unfavorable meteorological conditions are the external causes of heavily polluted weather, such as static stability, small wind, high humidity and inversion temperature, which will lead to more serious air pollution under the premise of basically unchanged emissions. The research shows that since the implementation of "Atmosphere Ten", the meteorological conditions of pollution in Beijing-Tianjin-Hebei region are generally unfavorable, which also increases the difficulty of pollution control. From the comparative analysis of meteorological conditions of pollution in Beijing, Tianjin and Hebei, the difference between 20 14 and 20 13 is 17%, 20 15 and 20 12%. In autumn and winter of 20 16, China once again experienced very unfavorable pollution. At the same time, there is interaction between air pollution process and meteorological process. When atmospheric pollution accumulates to a certain extent, the chemical composition of particulate matter (such as sulfate, black carbon and organic components) has a significant impact on radiation, which leads to the weakening of atmospheric diffusion ability of the boundary layer to a certain extent, thus further increasing heavy pollution.

In addition, the formation of heavily polluted weather is also affected by global climate change, which is manifested in global warming and makes the atmospheric stratification more stable, which has become international common sense. For example, since last autumn and winter, climate anomalies have generally occurred around the world, and many countries, including developed countries such as Britain, France and South Korea, have also experienced high-intensity and large-scale heavy air pollution.