Plants have a dual impact on haze, on the one hand it can sink, block and adsorb particulate matter, on the other hand emit plant-derived VOCs, the second generation of PM2.5, the impact on the atmosphere is very complicated.

Into April, ushered in the northern part of the catkins flew the peak. Cats not only give travel, life brings a lot of inconvenience, but also cause discomfort, sneezing, runny nose, poor breathing plagued many people. But catkins are not the most annoying. April 17, the northern region encountered the largest dust weather this year, once the Beijing PM2.5 concentration of heavy pollution. According to the Central Meteorological Station website news, April 30 to May 3, Huanghuai and other places there is intermittent mild haze weather; April 27 and April 29, the central Inner Mongolia, northern North China have Yangsha Or dusty weather.

Piled up, dust, mist and turmoil hit, often you sing it now that he has debut. On April 27, Yu Xinxiao, a professor at Beijing Forestry University, told SciDev.Net that in a major scientific research project entitled "Forest Regulation and Control of PM2.5 and Other Substances in the Forest", Beijing Haidian, Chaoyang and Fengtai In the six districts of the city, the annual total dust-holding capacity of all the plants is 9789 tons, and the reduction of PM2.5, PM10 and sand dust is effective. However, the flocculation and plant-derived VOCs (volatile organic compounds) Collaborative control must be used, tree species selection and other means to "increase blue and reduce haze."

The average concentration of PM2.5 significantly exceeded the complex causes

The air condition in April is a microcosm of the current complex air conditions in our country. At the 21st Symposium on Air Pollution Prevention and Control Technology, Wang Zhihua, secretary general of China Society of Environmental Science, said: "Air pollution is a prominent environmental issue facing our country and environmental pollution is grim in many areas. In 2016, The average ratio of days to standard cities is 78.8%, and the average concentration of PM2.5 is more than the standard.The causes of PM2.5 in our country are complex and have a wide range of sources, of which 50% comes from the direct emission of coal, motor vehicles, dust and biomass combustion and others come from Secondary pollution from the conversion of carbon dioxide, sulfur dioxide, nitrogen oxides in the air.

Wang Zhihua believes that air pollution control has achieved some success in recent years, but it still faces enormous challenges. "In particular, there is a big gap in controlling the accuracy of pollutants. If we are to pinpoint the target precisely, we must study how ozone and PM2.5 work together. To reduce PM2.5, besides controlling the emission of VOCs, Sulfur dioxide, smoke dust, ammonia and other pollutants to control. "

Willow to generate catkins also emit VOCs

VOCs is a general term for any organic compounds that can participate in atmospheric photochemical reactions, including alkanes, alkenes, aromatic hydrocarbons and various oxygenated hydrocarbons, halogenated hydrocarbons, nitrogenous hydrocarbons, sulfurous hydrocarbons and so on. The well-known formaldehyde, benzene is also a VOCs.

VOCs not only generate ozone, but also "precursors" to PM2.5. VOCs form secondary organic particles by coagulation, etc., and are converted into PM2.5. He Kebin, a professor at the Chinese Academy of Engineering and Tsinghua University, said: "VOCs, ozone and PM2.5 are related to each other."

However, at present, the concentration of VOCs in the air does not fall in the opposite direction. "It's a misunderstanding that many people get stuffy nose, sneeze, inflammation of the eyes, etc. when the plants bloom, not pollen particles that cause discomfort to the population, but when plants bloom VOCs, VOCs particle size is very small, after inhalation or PM2.5 inhalation of the human body, so allergic people have a variety of discomfort. "Yu Xinxiao said plants have a dual impact on haze, on the one hand is to sink, block and adsorption of particulate matter On the other hand, plant-derived VOCs are discharged and PM2.5 is generated twice. The impact on the atmosphere is very complicated.

"Our study found that different plants produce and emit VOCs in different numbers and quantities," said Yu Xinxiao, who said that shrubs emit alkenes, alkanes and alcohols, and that the emission amount is Euonymus japonicus> Euonymus japonicus> Euonymus japonicus. Deciduous trees, weeping willow will produce alkanes, alcohols; Platanus and Koelreuteria olefins, alcohols, Koelreuteria paniculata> weeping willow. Evergreen trees produce olefins, juniper> Qiao Song> Pinus tabulaeformis.

Yu Xinxiao said the number of different plant volatile organic compounds within a day will change over time, such as weeping willow willow, 12:30 to 13:00, is to produce benzene, alcohol and other VOCs peak.

The effect of forest dust removal is obvious but it will not weaken the wind

"At present, all kinds of parks and nature reserves in Beijing, the one million mu plain afforestation project, the Beijing-Tianjin sandstorm source management project and the forest belt formed by the Three-North Shelterbelt Project all play a role in smog protection in Beijing." Say.

Spread online, there is a saying that the Three North Shelterbelt blocks the strong winds from the north, making the wind speed in Beijing, Tianjin and Hebei smaller. The pollution in the air can not be "blown away" and smog increases.

"This statement is not correct." Yu Xinxiao said that the Three North Shelterbelt and other effects on the PM2.5 block, especially for the greater than the PM10 coarse particles, dust effect more pronounced. "Artificial forests grow 20-30 meters above sea level, but they can only affect the ground near the ground without damaging the gale at high altitude. And the air flow will soon resume after it passes through the forest."

During the 13th Five-Year Plan, the total amount of VOCs will drop by 10%

Professor Chen Jianmeng, Vice-Chancellor of Zhejiang University of Technology, said that there are natural sources, artificial sources, mobile sources and fixed sources in terms of VOCs emission.

According to the state requirements, the total amount of VOCs during the "13th Five-Year Plan" period will have to drop by 10%. For the first time, joint prevention and control of Beijing-Tianjin-Hebei region will also make VOCs one of the four major pollutants for the first time. Professor Ye Daiqi, Dean of the School of Environment and Energy at South China University of Technology, said that in man-made sources, the proportion of industrial sources accounts for half of the total, while that of mobile sources and living sources accounts for about 1/4 respectively. The industrial sources of VOCs emissions include the production, storage, and sales of coal chemical and petrochemical industries; the production and processing of boilers using VOCs as raw materials. 80% of mobile sources are sources of road movement; there are also consumer goods, fossil fuels, biomass burning and pesticide use.

"According to the current mode of production and lifestyle development, VOCs increase is very alarming." Yip Kai said that the total VOCs decreased by 10%, the reduction is not simply to reduce the original 10%, but to increase the amount also cut , "This is an absolute reduction."

Optimized configuration technology to achieve dust-proof sterilization

How to control catkins and reduce plant-derived VOCs? Yu Xinxiao said that Beijing is giving female willow trees that will produce catkins and injecting drugs and updating such problems as catkins by updating species of tree species

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