Why did the smog in Beijing disappear without cooling down?

On February 22nd last year (12) and February 22nd this year (12), the smog in Beijing suddenly disappeared without wind or cooling. The reason is explained by experts from a three-dimensional perspective.

Waiting for the wind is people's anxious expectation when there is fog. However, unlike the gale at the end of the smog on June 8, 1965, Beijing residents generally wondered that the smog disappeared without wind or cooling, at 438+06, 65, 438+02, 2065, 438+07, 65, 438+05. Then, can we get inspiration from the smog "disappearing in place" incident and formulate effective measures to control smog? Related speculations are widely forwarded in the circle of friends.

In this regard, Jiang Dahe, a blogger of Science Network and a professor at Tongji University School of Environmental Science and Engineering, published a blog post, questioning that the smog dissipation process should be explained in three dimensions, and this complex frontal process played a role.

When the reporter visited environmental and meteorological experts, he also got the answer that "smog will not disappear on the spot", but in the three-dimensional dynamics of air flow, there has been a concentration change that the human body on the ground can't detect.

The smog just disappeared?

There is no strong wind, sunny and warm, where did the smog go?

Hui Jin, a member of Friends of Nature, published an article about the "disappearance" of smog on February 22, 20 16, which gained a high reading volume and reprint rate.

He proposed: "According to data observation, the smog index of many stations in Beijing 14 site dropped by as much as 400 points in an hour or two, and no diffusion and transfer of pollutants were found. There is no sign of strong wind blowing. Where did the smog go? "

By comparing and analyzing the real-time indexes of several monitoring stations in Beijing, Hui Jin thinks that for this severe smog that lasted from February last year 16 to the early morning of the 22nd, it was more than 120 hours. "In the final stage, no matter whether you look at each station or the whole Beijing, the suspended pollution particles in the atmosphere basically did not exist or did not spread to the outside world at all.

So is the smog "disappearing on the spot", or are there any meteorological phenomena that we have ignored, or are there other reasons?

Cold air blowing haze is a frontal process.

With full of doubts, the reporter of China Science News contacted Jiang Dahe. He responded: "Is the pollution index in the relevant area going through a process of rising and then falling for several hours? This is an idea of plane propulsion, which explains the phenomenon discussed in two-dimensional space. "

Jiang Dahe observed that after February 16 last year, the meteorological cause of smog pollution in Beijing, Tianjin and Hebei was the prevalence of warm and humid airflow, which lasted for many days. Until the early morning of February 22, 65438, a strong cold air entered Beijing from the north-northwest direction, and the direction was south-southeast

"This is the meeting of two different air masses: one is wet, warm and polluted, and the other is dry, cold and clean." There is a frontal process near the interface where the cold air mass pushes the warm air mass south. Different air masses will basically maintain their own characteristics, but only mix near the interface.

The distribution of temperature, humidity, air pressure and wind force during the frontal process is very complicated, which is related to the strength, wind speed, wind direction and topography of the air masses on both sides. The mixed layer will be destroyed and produce vertical movement, which may be accompanied by precipitation. It is easy to imagine that it is a three-dimensional dynamic. And "pollutants are easily blown away in the sky, and the ground monitoring results cannot explain all the problems." Jiang Dahe further explained, "The cold air in Beijing went south on February 22, 65438 last year, which seems to belong to a weak cold front process in winter."

At the same time, although the transmission, diffusion and accumulation of smog in Beijing from 20 16 to 12-22 are not obvious, Jiang Dahe believes that the smog in Beijing, Tianjin and Hebei is actually transported to the south by consulting the national smog distribution map.

However, since the cold wind blows away the smog, why can't it feel cool? "The cold air mass is too weak." Jiang Dahe replied to the reporter, "This is also the reason why the smog has gone and hurried back."

The horizontal wind is strong, and pollutants spread to the upper layer.

Meteorologists also explained the "disappearance" of smog from a three-dimensional perspective.

Taking the smog "disappearing" on June 2, 65438 as an example, Zhang Hengde, deputy director of the Environmental Meteorological Center of China Meteorological Bureau, said that since the early morning of the 2 nd, although the ground wind speed was very low, the human body did not feel obvious, but at a height of 200~3000 meters from the ground, the northerly wind was very obvious, and the northerly wind came earlier than the ground wind.

The pollutants in the air are distributed vertically, and when the horizontal wind is strong, the pollutants will also spread vertically. "When the cold air arrived in Beijing, the thickness of the smog had reached 800 meters. It happens that the ground wind is very small, but the northerly wind at a height of 200 meters is obvious, so the reduction effect is obvious. " Zhang Hengde told the reporter of China Science Journal. However, unlike the process of 65438+February 22 last year, due to the weak cold air mass on June 2, "the whole air layer began to southward at noon on the 2 nd, and the smog came back soon."

As Hui Jin once mentioned: "Severe smog has always been the cause: large pollutant emissions are the root cause, and meteorological conditions that are not conducive to diffusion are the direct cause." It is true that when the smog dissipates, we still need to wait for the change of meteorological conditions.

Liu Hongli, an associate researcher at China Institute of Meteorological Sciences, said in response to a reporter's question on June 7, 65438+/KLOC-0, that unless there is human intervention, such as closing factories, the pollution discharge level will not generally fluctuate greatly. Meteorological conditions drive smog changes, and high pollution and poor meteorological conditions form smog events. If it rains or blows, it can clear the smog. Under the same emission conditions, the role of meteorological factors exceeds 70%.