Focus interview丨Clear blue sky does not mean good air! Be alert to invisible pollution
In the long summer afternoon, the sky is clear and transparent, but it is also possible that a kind of air pollution is hidden in it.
There is a layer of ozone at a height of about 20-50 kilometers from the surface of the earth, which can absorb most of the ultraviolet rays in the sun and protect the creatures on the earth from harm.
But near the ground, ozone is a pollutant that is harmful to humans.
Moreover, near-Earth ozone is not only a health killer, but also causes crop losses.
This year is the closing year of my country's "Three-year Action Plan for the Defense of the Blue Sky". While PM2.5 governance has achieved significant results, ozone pollution is becoming a new environmental problem.
The blue sky in the summer afternoon is often the time of the day when the ozone concentration is highest.
In a year, the ozone concentration generally starts to increase in May, reaches its highest point in July and August, and gradually decreases after autumn.
The secondary standard limit of ozone concentration set by our country is 160 micrograms per cubic meter.
In recent years, many cities across the country have experienced excessive ozone levels.
Since the "Thirteenth Five-Year Plan", the concentration of ozone pollution in my country has been increasing year by year.
On June 2 this year, the National Bulletin on the State of the Ecological Environment in China 2019 released by the Ministry of Ecology and Environment showed that in 2019, 30% of the country’s 337 cities had ozone exceeding the standard. Among them, ozone pollution in the Beijing-Tianjin-Hebei and Yangtze River Delta regions was particularly prominent.
In 2019, the number of days exceeding the standard with ozone as the primary pollutant accounted for 41.8% of the total number of days exceeding the standard, second only to PM2.5 (fine particulate matter), which accounted for 45%.
Ozone has strong oxidizing properties.
Ozone near the ground is a harmful gas, and can even become a "health killer".
If the ozone concentration in the air is too high, it is easy to cause inflammation of the upper respiratory tract, cough, headache and other symptoms, and it will also cause irritation to the skin, eyes, and nasal mucosa. On the other hand, too high ozone concentration will also affect the ecological environment. Cause a negative impact.
So how is this ozone produced, and why has the ozone concentration in our country been rising?
According to reports, nitrogen oxides and volatile organic compounds (VOCs) are the two "raw materials" that produce ozone, and are called ozone precursors.
They undergo a photochemical reaction under the ultraviolet rays in the strong sunlight to produce ozone.
The higher the temperature and the longer the illumination time, the greater the amount of volatilization and the fuller the degree of reaction, so the ozone concentration tends to be higher.
Yan Gang, deputy director of the Environmental Planning Institute of the Ministry of Ecology and Environment: There
are several aspects of nitrogen oxide emissions. One is traffic sources, and the second is industrial sources, mainly fossil energy, including nitrogen oxide emissions caused by industrial fuel combustion.
Chai Fahe, Chief Scientist of the Chinese Academy of Environmental Sciences
:
Due to the growth of gasoline consumption, the development of the petrochemical industry and the chemical industry, coupled with the use of a large number of architectural coatings, including road paving, the use of paint, and the printing of printed materials, etc. And so on, these links are causing the overall VOCs (volatile organic compounds) emissions to increase.
An increase in the concentration of precursors will inevitably lead to an increase in the amount of ozone generated later.
VOCs, also known as volatile organic compounds, come from a wide range of sources. Generally speaking, they include natural sources and man-made sources.
The anthropogenic source mainly refers to the pollutants discharged in the process of human production and life.
Urban areas mainly include motor vehicle exhaust emissions, oil volatilization leakage, industrial enterprise emissions, solvent use emissions, liquefied petroleum gas (LPG) use, daily necessities, etc.
In recent years, my country has continuously strengthened the control of VOCs and nitrogen oxide emissions.
The "Three-Year Action Plan for Winning the Blue Sky Defense" issued in 2018 specifically pointed out the need to strengthen the rectification of VOCs.
In May of this year, the Ministry of Ecology and Environment clearly pointed out at a press conference that my country’s current ozone generation is mainly controlled by VOCs.
On June 24 this year, the Ministry of Ecology and Environment issued the "2020 Volatile Organic Compounds Governance Tackling Plan", requiring that summer VOCs tackling operations be placed in an important position as a key measure to win the blue sky defense war.
VOCs are common precursors for PM2.5 and ozone.
In recent years, Beijing has experienced excessive ozone levels. Therefore, the emission control of VOCs has always been a key area of Beijing’s air pollution prevention and control.
In the past few years, Beijing has carried out several special control actions against VOCs emissions, one of which is the control of emissions from mobile sources.
In order to further precisely control the operation of the continuous oil and gas recovery system of gas stations, from 2017 to 2018, Beijing installed oil and gas recovery online monitoring systems in some gas stations with large sales.
The fueling guns, tanks and other oil and gas recovery facilities are monitored 24 hours a day. Once a problem occurs, an alarm will be issued soon, which shortens the running time of the equipment and reduces abnormal volatilization of oil and gas.
At present, mobile sources are one of the main sources of VOCs emissions in Beijing. In recent years, Beijing has strengthened the control of mobile sources in different ways.
Hua Fei, the first-level chief officer of the Atmospheric Environment Division of the Beijing Municipal Bureau of Ecology and Environment:
From the perspective of the main emission reduction measures, there are mainly two types. One is to continuously strengthen vehicle fuel standards in oil products; the second is Promote the emission reduction of motor vehicle structure.
From 2013 to 2019, more than 2 million old motor vehicles were scrapped and transferred out in Beijing; the electrification of vehicles was vigorously promoted, and a total of 337,600 pure electric vehicles were promoted.
Accumulatively, more than 3,000 general manufacturing and polluting enterprises that do not meet the functional positioning of the capital have been withdrawn, and 12,000 "scattered and polluting" enterprises have been eliminated.
According to preliminary calculations, in 2019, Beijing's anthropogenic VOCs emissions decreased by 48.8% compared with 2015.
In addition to emissions from mobile sources, VOCs also have many emission sources, especially in a wide range of industries.
At present, source substitution has gradually become a major governance method.
In Huzhou, Zhejiang, Nanxun District uses more oil-based paints in industries such as wood, motors, elevators, etc., so VOCs control tasks are heavier.
For this reason, in the past few years, Nanxun District has gradually changed the old way of mainly relying on the improvement of terminal pollution control facilities in the past, and promoted water-based paint instead of oil-based paint in these industries.
In the sheet spraying workshop of an automobile service company in Nanxun District, the staff are painting in the operation room, and at the same time, the personnel of the environmental department have tested the VOCs content in the workshop.
Sun Fangfang, Deputy Section Chief of the Atmospheric Environment Division, Nanxun Branch of the Zhejiang Huzhou City Ecological Environment Bureau:
When using oil-based paint, the data has to reach more than 1,000. Now we have measured only a few tenths, far below the national standard.
The wood industry is a traditional advantageous industry in Nanxun District.
However, it has long been plagued by "low, small, scattered, chaotic, and pollution", so Nanxun District has made great efforts to carry out industry-wide rectification.
Control the volatile organic compounds (VOCs) generated in the process of painting, spraying, and hot pressing.
Although there have been quite effective treatment methods, since VOCs have many emission points and scattered emission characteristics, the past regulatory measures and methods are not fully applicable.
At the same time, there are many types of industries in China, and the management level of enterprises is uneven. Therefore, the supervision and management of ozone pollution in my country still faces considerable challenges.
Yan Gang, deputy dean of the Environmental Planning Institute of the Ministry of Ecology and Environment: The
overall control of VOCs in our country started relatively late, it is indeed complicated, and the governance is more difficult.
During the "14th Five-Year Plan" period, synergy will become a main theme in the field of atmosphere. Whether it is to control PM2.5 or solve the problem of ozone, it needs to be strengthened.
In the reduction of VOCs and nitrogen oxide pollution, one is that the control indicators reflect synergy, the second control area reflects synergy, and the third control measure reflects synergy. Through these synergy, including policy synergy, greater environmental effects can be achieved with lower social costs.
Summer ozone pollution has become an important "blocker" in winning the battle to defend the blue sky. Together with PM2.5 pollution in autumn and winter, it has become the "two mountains" in front of us.
According to reports, the Ministry of Ecology and Environment organized 95 cities in the Beijing-Tianjin-Hebei region and surrounding areas, the Yangtze River Delta region, the Fenwei Plain and the junction of Jiangsu, Anhui, Shandong and Henan to carry out summer ozone control operations.
Through the joint efforts of various departments at all levels, the ozone concentration in key regions, provinces and cities decreased significantly from June to August, and the number of days when ozone exceeded the standard was significantly reduced. There was no obvious, large-scale regional ozone pollution process.
In the preparation of the special plan for the prevention and control of air pollution during the 14th Five-Year Plan, the emission reduction targets have been specifically designed for the two precursors of ozone.
Promote high-quality development on the one hand, and pay more attention to ecological construction on the other hand, with the participation of all people and joint action. Our blue sky will definitely be fresher and cleaner.