When does foggy weather often happen?

Since the beginning of the year, most parts of the country, including Shijiazhuang, have suffered from serious air pollution, which has aroused widespread concern. The municipal government of Shijiazhuang attached great importance to it and responded positively. With the determination of the last battle, we launched a tough battle to improve the ecological environment with the main contents of controlling environmental pollution, promoting industrial transformation and carrying out tree planting and greening, which promoted the continuous improvement of the ecological environment in our city and vowed to return the provincial capital to a new blue sky.

So, how is the smog formed? Why is there so much smog this year? How to solve the dilemma of air pollution? What effective measures have we taken to control air pollution? What other aspects should we focus on in the face of the present situation?

Haze is closely related to meteorology and sewage discharge.

At the beginning of this year, there were large-scale and long-term smog weather in many areas in central and eastern China, and 30 provinces (autonomous regions and municipalities) such as Shijiazhuang were shrouded in smog. In Beijing, Tianjin, Shijiazhuang and other cities, due to the long-term accumulation of air pollutants near the ground at low altitude, serious air pollution and serious pollution have occurred continuously in the main city. For a time, once unfamiliar words such as "smog" and "PM2.5" suddenly entered the lives of ordinary people. What is the cause of smog? Become a hot spot of everyone's attention.

"Fog and haze are actually two different weather phenomena. Fog is a large number of tiny water droplets or ice crystals floating in the air. Haze refers to the turbidity caused by the suspension of a large number of particles such as smoke and dust. Large-scale haze weather mainly occurs in large-scale atmospheric circulation with weak cold air and good water vapor conditions. One of the necessary conditions is low altitude near the ground or wind or breeze. " Zhao Yanchang, a senior engineer of the Municipal Meteorological Bureau, said: "Autumn and winter are a season with low temperature and weak ground pressure field. The wind near the ground is weak, there is no cold air activity, the atmospheric stratification is relatively stable, and there is an inversion layer near the ground, which is not conducive to the dilution and diffusion of pollutants. If the humidity is high at this time, it is easy to form haze weather. "

The common sense is that when there is fog, it often means that the atmosphere is relatively stable, and the stable atmosphere is easy to accumulate pollutants, so foggy weather is often accompanied by mild or severe pollution. Many times, the low visibility weather in central and eastern China is actually caused by some smog mixture. When the relative humidity is high in the morning, it is mostly fog, and it turns into haze after the temperature rises and the humidity drops during the day.

So what are the substances that make up the smog? According to the data of China National Environmental Monitoring Center, particulate matter (PM2.5 and PM 10) is the main pollutant that has the most significant impact on air quality during this continuous smog process.

Changan D, the deputy station of the Municipal Environmental Monitoring Center, revealed that PM 10 and PM2.5 come from various pollution sources, such as coal-fired emissions, motor vehicle exhaust emissions, all kinds of dust, industrial emissions and volatilization, domestic source emissions, biomass combustion emissions and external pollution in surrounding areas. "according to an.d., the PM2.5 we usually hear includes primary pollutants and secondary pollutants. Primary pollutants mainly come from direct emissions from fossil fuel combustion, such as coal burning and automobile exhaust emissions. Secondary pollutants are mainly a series of reactions of primary pollutants in the atmosphere, which generate new pollutants different from primary pollutants, such as nitrate, aerosol and other secondary particles formed by chemical reactions of gaseous pollutants such as nitrogen oxides and VOC discharged from motor vehicle exhaust into the atmosphere.

"In addition to the above pollution, we should also know that every time electricity is used, it consumes 350 grams of coal, and the car consumes 0. 12 liter of gasoline every kilometer. Heating will eventually consume a lot of coal. The combustion of coal and oil will produce a lot of pollutants, such as sulfur dioxide, nitrogen oxides, dust, particles and heavy metals. Automobile exhaust is one of the main sources of urban PM2.5 and the chief culprit of smog weather and air pollution. " Ann de said.

The still wind has caused more smog this year than in previous years.

Haze is not a weather phenomenon only this year. In recent years, every autumn and winter, especially after winter, the central and eastern regions of China will encounter such weather from time to time. Why is there so much smog this year?

"The number of haze weather is obviously related to the atmospheric circulation in that year." Chen Jing, a senior engineer of Shijiazhuang Meteorological Bureau, said that there is less haze in years with frequent cold air activities and more haze in years with frequent cold air activities. For example, 20 10, in recent years, the foggy weather in our city is less, with 3 days of fog and 23 days of haze, which is obviously less than the average of previous years, and there are more days with excellent atmospheric air quality. "During the period of 65438+February in 20 12, there were less foggy weather, mainly due to frequent cold air activities." She said.

Meteorologists believe that large-scale haze weather mainly occurs in a large-scale atmospheric circulation situation with weak cold air and good water vapor conditions. One of the necessary conditions is that there is still wind or breeze at low altitude near the ground. "From 1 to February this year, the average wind speed in our city was only 1. 1 m/s, the number of windy days less than 1.5 m/s reached 54 days, and the frequency of small winds was 92%. In the same period last year, it was 5 1 day, and the frequency of small winds was 85%. " Zhao Yanchang said that since the beginning of this year, the frequency of quiet wind in our city has been 86 hours, 37 hours more than the same period last year. "Such a small wind speed is very unfavorable to the diffusion of pollutant levels. In addition, snowfall is more frequent this year. Although snowfall can reduce the pollution concentration in the air, the humidity after snowfall is high. If there is no new cold air invasion, it is more prone to continuous foggy weather. "

Ma Xuekuan, chief forecaster of the Central Meteorological Observatory, said that due to the quiet weather near the ground, regardless of the size of the city, pollutant emissions from local transportation, life and production are accumulating at low altitude. Due to the high humidity and high water vapor in foggy days, fog droplets provide adsorption and reaction sites, which accelerate the transformation of reactive gaseous pollutants into liquid particulate components, and particulate matter is also easy to act as condensation nuclei to accelerate the formation of smog, and the interaction between them quickly forms pollution.

The construction of ecological environment, including the control of serious air pollution, has always been highly valued by the municipal party committee and municipal government, and Sun Ruibin, member of the Standing Committee of the Provincial Party Committee and secretary of the municipal party committee, has elevated it to the height of "saving lives". In only 20 12 years, the city dismantled 468 scattered coal-fired boilers in urban areas, shut down and banned 25 building materials enterprises, eliminated 90 cement plants, completed 378 dust control projects in construction sites, banned 7 19 coal-fired stoves in urban catering units, eliminated 47,000 yellow-label vehicles, and promoted low sulfur. A total of 422,200 tons of coal was cut, 59 10.8 tons of smoke and dust and 6,755.2 tons of sulfur dioxide were reduced.

However, freezing three feet was not built in a day. During the "Eleventh Five-Year Plan" period, under strong control, the national sulfur dioxide concentration and emissions decreased significantly. However, due to the huge emissions of pollutants such as sulfur dioxide, nitrogen oxides and volatile organic compounds, the degree of air oxidation is getting higher and higher, and the activity of pollution factors is increasing. Many pollutants undergo complex chemical reactions and generate secondary PM2.5 again.

"the treatment of pollutants such as PM2.5 requires comprehensive means to achieve coordinated emission reduction of various pollutants. Pollution control is a multi-link closely meshed chain. As long as there is a link' off the chain', PM2.5 emission reduction will be affected. " Environmental experts said.

The uniqueness makes Shijiazhuang suffer from smog more serious.

Among the smoggy weather that covers most parts of the country, the smog in Shijiazhuang is relatively more serious. What caused this?

"Shijiazhuang City is located in the eastern foot of Taihang Mountain, with high terrain in the west and low terrain in the east. The average elevation of the western mountainous area is 500 ~ 700 meters, and the average elevation of the eastern plain is 30 ~ 70 meters, showing a' safe haven' terrain. Shijiazhuang has a warm temperate continental monsoon climate, and northwest winds prevail in winter. However, under the influence of the mountain barrier in the west, it is difficult for cold air from the west to enter the urban area, resulting in less gale frequency, low wind speed, more static wind frequency, high inversion frequency and poor atmospheric diffusion conditions. In this way, pollutants accumulate at the bottom of the atmosphere and are difficult to spread, forming an' urban pollution valley' phenomenon in which pollutants are constantly circulating, which has aggravated air pollution in urban areas. " Zhao Yanchang said.

In addition to its unique geographical location, air pollutants in Shijiazhuang are not easy to spread, and the transport of foreign pollutants on various scales is also a factor in the haze weather in Shijiazhuang. "Hebei province is surrounded by surrounding urban agglomerations and is obviously transported by foreign pollutants of various scales. From Shijiazhuang to Cixian in southern Hebei, from Shijiazhuang to Tianjin are two obvious pollutant gathering areas. " According to Su Fuqing, an environmental expert, Shijiazhuang area is the intersection of two convergence zones, which leads to the increase of PM 10 value in this area. Because the convergence zone occurs in the plain area in front of Taihang Mountain and Yanshan Mountain, it becomes the convergence type of piedmont plain. The southern foot of Taihang Mountain is the intersection of Taihang Mountain wind and northeast wind in Hebei Plain. It is an anticyclone belt from Tianjin to Shijiazhuang, and a southwest wind belt from Taiyuan Basin through Yangquan. The two belts meet in Shijiazhuang, which leads to the accumulation of pollutants in this area.

The special geographical environment caused the haze weather in Shijiazhuang. In addition, Shijiazhuang's coal-based energy structure, extensive economic development mode, unreasonable industrial structure and layout, and the substandard exhaust emissions caused by more and more cars are the direct culprits of haze weather.

Some environmental experts believe that the main human factors causing smog are coal burning, automobile exhaust, dust and industrial pollution. At present, the amount of coal and the number of motor vehicles in our city are still increasing; There are 6 12 construction sites in Shijiazhuang city alone, and some dust prevention measures are not in place; The secondary dust from traffic roads such as national highways and provincial highways, especially the main coal transportation channels in western counties (districts), is still heavy, which is an important reason for the increase in PM2.5 emissions. Although our city has been stepping up efforts to dismantle scattered coal-fired boilers, at present, our city's energy consumption is still dominated by coal, and the total amount of coal is increasing year by year.

Except that the energy structure is still dominated by coal, the economic development mode of our city is still extensive, and the industrial structure and layout are not reasonable. According to the analysis of industrial output value above designated size in 20 1 1, the top ten industries contributing to the economy are ferrous metal smelting and rolling processing, chemical raw materials and products manufacturing, leather, fur, feather (velvet) and its products, agricultural and sideline food processing, textile, non-metallic mineral products, pharmaceutical manufacturing, general equipment manufacturing, petroleum processing, coking and nuclear fuel processing. These ten industries account for 69.8% of the total industrial output value above designated size, and the average energy consumption of output value is 0.5 1 ton of standard coal/10,000 yuan, which is higher than the average level of the whole city. From the analysis of pollutant emission ratio, the sulfur dioxide and nitrogen oxides emitted by the above ten industries account for 94.6% and 98.5% of the sulfur dioxide and nitrogen oxides emitted by industrial enterprises above designated size respectively. In addition, there are still enterprises with large emissions of pollutants such as medicine, steel and thermoelectric in the urban area of our city.

If all kinds of reasons are combined with unreasonable spatial layout, it is not surprising that pollutants in urban areas will intensify and gather when urban heat island effect and static weather phenomenon are obvious.