China News Service, September 11, "Pollutant emissions exceed 50% of the environmental capacity, which is the root cause of frequent heavy pollution." Talking about the main causes of air pollution in the autumn and winter in Beijing-Tianjin-Hebei and surrounding areas, ecological environment Deputy Minister Zhao Yingmin made the above statement on the 11th.
Data map: Smoggy day.
Photo by China News Agency reporter Li Huisi
The Information Office of the State Council held a regular policy briefing by the State Council on September 11, introducing the status of science and technology in helping to win the blue sky defense war.
A reporter asked at the meeting, through research on key projects, what are the main causes of air pollution in the autumn and winter in the Beijing-Tianjin-Hebei region and surrounding areas?
What are the main sources?
"In order to fully understand the causes of regional heavy pollution, the research project designed a closed research technology system combining comprehensive observation, experimental analysis, and digital simulation that confirmed each other, and built the largest regional air-space-ground integrated three-dimensional observation network in China to track heavy pollution in real time. The occurrence, development, transmission and dissipation of the pollution process, dynamic grasp of the component changes in the polluted atmosphere and pollution sources, from the four aspects of pollutant discharge, chemical conversion, changes in meteorological conditions, and pollution transmission, it fully clarifies the regional autumn and winter The cause of pollution." Zhao Yingmin said.
Zhao Yingmin pointed out that, to sum up, there are four factors that work together to cause the occurrence of heavy pollution in the region:
First, the discharge of pollutants exceeds 50% of the environmental capacity, which is the root cause of frequent heavy pollution.
"Beijing-Tianjin-Hebei and its surrounding areas, which is what we often call the '2+26' cities, are highly concentrated in heavy chemical industries. The energy utilization methods in the region, mainly by coal, and the freight transportation methods by road transportation, have led to regional The emissions of major air pollutants in China remain high. The emissions of major pollutants per unit of land area are 2-5 times the national average, and the multiples of different pollutant emissions are not the same." Zhao Yingmin said, in addition to sulfur dioxide, within the region The discharge of major pollutants exceeds 50% of the environmental capacity, and some cities even exceed 80%-150%.
In addition, the main pollutant emissions in autumn and winter, due to heating reasons, increased by about 30% more than usual.
In general, the discharge of pollutants in the region exceeds the environmental capacity, which should be the root cause of frequent heavy pollution.
The research project set up 109 sampling points in the "2+26" cities, collected more than 58,000 samples, and measured 490,000 chemical component data online.
The analysis of the sources of PM2.5 in the autumn and winter of 2018-2019 shows that the contribution of industrial and civilian coal and diesel vehicles to regional PM2.5 reached 36%, 17% and 16%, which are the three largest contributions. The main source of heavy pollution.
Among the industrial sources, the iron and steel coking industry contributed the most, followed by the cement industry.
The second is the high concentration of nitrogen oxides and volatile organic compounds in the atmosphere, resulting in increased atmospheric oxidation, which is a key factor in the rapid increase of secondary PM2.5 during heavy pollution.
Part of PM2.5 is directly emitted, but part of it is due to gaseous pollutants emitted into the air. Sulfur dioxide, nitrogen oxides, etc., through secondary conversion, form fine particulate matter in the air. This part of PM2.5 is called secondary Converted PM2.5.
With the continuous deepening of air pollution control, the proportion of primary components has dropped significantly, and the proportion of secondary components converted from air pollutants into particulate matter has continued to rise.
Since 2013, the proportion of secondary components has gradually increased, from 40% to 50%. During periods of heavy pollution, secondary pollutants are the main component of particulate matter, and the proportion can reach 60% or even higher. .
The high concentration of nitrogen oxides and VOCs in the area will cause rapid photochemical reactions in the atmosphere, resulting in a high level of atmospheric oxidation, which is a decisive factor in promoting the conversion of air pollutants into secondary PM2.5.
The atmospheric oxidation of Beijing is about 2-3 times higher than that of London and Tokyo.
The high oxidizability also causes the secondary conversion rate to increase 3-5 times during the period of heavy pollution in the area.
On the one hand, atmospheric oxidability promotes the conversion of gaseous pollutants into PM2.5, and it also promotes the formation of ozone in summer.
Therefore, controlling atmospheric oxidation is the next step and the key point of coordinated control of PM2.5 and ozone. It has the effect of "two birds with one stone".
Third, unfavorable weather conditions have led to a significant reduction in regional environmental capacity, which is a necessary condition for the formation of heavy pollution weather.
The Beijing-Tianjin-Hebei region and its surrounding areas are located in the semi-enclosed terrain on the east side of Taihang Mountain and the south side of Yanshan Mountain. Therefore, there is objectively a "weak wind area". At the same time, above this area, the troposphere has a "warm cover" structure.
Atmospheric diffusion conditions are "congenital insufficiency". This is mainly because the diffusion conditions in this place are poor compared to other places, which leads to a small environmental capacity.
Affected by climate change, since 2000, the overall regional environmental capacity has shown a downward trend.
In addition, the environmental capacity also shows quarterly and monthly differences. One important reason why the air is good in summer is the good air diffusion conditions.
In addition, each month and year are also different due to changes in meteorological factors.
In general, the environmental capacity in autumn and winter is on average about 30% smaller than that in spring and summer, and the environmental capacity in January is about half of that in July.
Therefore, once the wind speed near the ground is less than 2m/s, the height of the boundary layer caused by temperature inversion drops below 500m, and the relative humidity is higher than 60%, the atmospheric environmental capacity will be further reduced by 50%-70%, so it is very easy to induce Heavy pollution weather.
The first factor is high emissions.
At the same time, because this area is full of mountains to the west and north, the environmental capacity is inherently insufficient. In winter, the capacity is reduced by half compared with summer. When the two factors are added together, it is prone to heavy pollution.
Fourth, regional transmission has a significant impact on PM2.5. The average contribution rate of each city is about 20%-30%, and it further increases to 35%-50% during heavy pollution.
At the beginning of air pollution control, often because local emissions are relatively high, local sources have a relatively large impact on local environmental quality.
With the deepening of pollution control, the proportion of local sources has gradually decreased, and external inputs have gradually increased.
The key research project analyzed nearly a hundred severely polluted weather processes since 2013, and showed that during the period of heavy pollution, the average contribution rate of regional transmission to Beijing’s PM2.5 was about 45%, and individual processes could reach 70%. There are mainly three transmission channels in the area, which is also the conclusion of this research project after research and observation.
One channel is the southwest channel, that is, the northern Henan-Handan,-Shijiazhuang-Baoding-Beijing line. This channel has the highest transmission frequency and the highest transmission intensity. The average contribution rate of the heavy pollution process is about 20%, and the individual heavy pollution process can reach 40%. .
The second channel is the southeast channel, which is along the central part of Shandong-Cangzhou-Langfang-central and southern Tianjin.
The third channel is the easterly channel, which is the Tangshan-Northern Tianjin-Beijing line.
Zhao Yingmin said that these four reasons are superimposed on each other, resulting in the occurrence of heavy pollution in the region in autumn and winter.
More governance is to focus on man-made emissions and greatly reduce pollutant emissions, so that even if extreme adverse weather conditions are encountered, heavy pollution will not occur again.