Pollution emissions are relatively stable in winter, why are more haze days
Our reporter Fu Lili
In the past few days, the people living in Beijing and the central and eastern part of our country were covered by smog.
Every winter, the haze will come unexpectedly, which is annoying.
Why does the number of smog days seem to increase in winter? What are the main causes of smog in my country? What impact does global warming have on smog, and what control measures should be taken?
On the 12th, at the Meteorological Science Lecture Room hosted by the China Meteorological Administration, Zhang Xiaoyi, an academician of the Chinese Academy of Engineering and a researcher of the Chinese Academy of Meteorological Sciences, answered all these questions of public concern.
Excessive coal consumption is the main cause of smog in my country
When it comes to smog, we have to mention aerosols.
"Fog and haze are related to aerosol particles." Zhang Xiaoyi said that atmospheric aerosol is the general term for solid and liquid particles suspended in the atmosphere. Surface soil, ocean, and vegetation are the main natural sources of aerosol particles, while man-made emissions are the main sources. It is fossil fuels, biomass burning, land use, land cover changes, such as urbanization, coatings, and chemical industries.
Zhang Xiaoyi said that the World Meteorological Organization uses visibility to define fog and haze. Too many small water droplets in the air can also reduce visibility. When the visibility caused by small water droplets is less than 1 km, it is called fog; it is caused by aerosol particles and hygroscopicity. When the visibility caused by aerosol is less than 10 kilometers, it is called haze.
Fog and haze in the past are natural phenomena, and aerosols are background aerosols. The aerosols as cloud condensation nuclei mainly come from natural processes. Nowadays, both fog and haze are related to aggravated aerosol pollution.
"There are two main factors affecting my country's smog: one is emissions, and the other is meteorological conditions. Among them, the most fundamental reason is the excessive consumption of unclean energy, mainly coal." Zhang Xiaoyi emphasized.
Taking China and the United States as examples, Zhang Xiaoyi calculated an account. Both countries have an area of more than 9 million square kilometers. In 2013, my country consumed about 2.5 billion tons of coal, while the United States consumed 800 to 900 million tons. About 300 square kilometers of the central and eastern parts are consumed, which makes my country's atmospheric aerosol pollution very serious.
How does climate change affect haze pollution
Some members of the public may also ask whether climate change has exacerbated the haze weather?
In this regard, Zhang Xiaoyi explained that various meteorological factors are more or less related to air pollution, but each cannot fully and linearly reflect the degree of pollution.
For this reason, their team has been tackling key problems and finally developed an unfavorable weather index that integrates various weather conditions.
The index shows that climate warming has an impact on regional haze pollution, but it does not play a leading role. Pollution emissions are still the main cause.
So, why does it seem that there are more smog days in the winter, when pollution emissions are relatively stable?
"In the stable stage of emissions, unfavorable weather conditions are necessary external conditions for the emergence of pollution." Zhang Xiaoyi said.
In daily life, many people have this experience. The weather in the afternoon is still slightly polluted, but it becomes severe at night or night.
In fact, who is the culprit of this "explosive growth" in the later period is also a core issue that has plagued scientists for a long time.
Zhang Xiaoyi pointed out that his team’s long-term research has found that after pollution accumulates to a certain level, meteorological conditions will be further deteriorated. At this time, there will be phenomena such as temperature inversion, low-level humidification, and surface radiation-turbulence weakening. Due to the weakening of turbulence, the boundary layer The height will be compressed to 1/3 of the initial stage of pollution, forming a significant two-way feedback mechanism.
"The mechanism of'two-way feedback' is that aerosols weaken the solar radiation reaching the ground, inhibit the development of the boundary layer, and significantly reduce the ability of all pollutants to'dilute' in the horizontal and vertical directions. It is it that dominates the explosive growth of PM2.5 in the later stage of pollution. ." Zhang Xiaoyi said.
In view of the excessive use of unclean energy (mainly coal) is the most fundamental reason for the serious smog in my country.
Zhang Xiaoyi suggested that the future pollution reduction is still the focus, such as controlling the total coal consumption, increasing the use of natural gas and non-fossil fuels; strengthening the clean use of coal, reducing man-made emissions, and controlling motor vehicles, focusing on non-road vehicles and large trucks. Wait.
(Science and Technology Daily, Beijing, November 12)