Recently, the 2014 China Urban Academic Year Conference, with the theme of "urban diseases" and urban governance, was held in Hangzhou. At the sub forum on urban ecological environment, experts discussed issues such as where fog and haze come from, why haze is difficult to dissipate, and how to treat urban diseases.
Where does haze come from
Researcher Zhang Xiaoyi, Vice President of the Chinese Academy of Meteorological Sciences, believes that fog and haze are two natural weather phenomena. In the past, fog was a soluble part of the large amount of carbon containing gases emitted by vegetation, and it was a natural process. But now, both fog and haze are related to the worsening aerosol pollution behind them. In the past two to three decades, the problem of haze in the central and eastern regions of China has become increasingly serious, mainly due to a significant increase in anthropogenic emissions of atmospheric aerosols. In other words, whether it is haze or fog today, there are a large number of aerosol particles related to human activities behind it, including PM2.5, which is often mentioned, and is no longer a completely natural phenomenon.
In big cities, car exhaust pollution is very serious. He Hong, a researcher at the Ecological Environment Research Center of the Chinese Academy of Sciences, pointed out that although urban air pollution in China was restricted by the energy structure dominated by coal, it showed obvious soot pollution characteristics in the early stage, but with the rapid increase of urban car ownership, nitrogen oxide pollution in large cities gradually increased, which made China's air pollution increasingly present a trend of compound pollution, that is, it is composed of soot pollution, vehicle exhaust pollution and other pollution.
"In urban air pollution, urban motor vehicle pollution is actually more difficult to control than the pollution caused by industrial smoke. The problem of industrial smoke can be solved through industrial transformation and upgrading and energy structure adjustment, but due to the upgrading of motor vehicle emission standards only targeting new cars, controlling urban motor vehicle exhaust pollution is bound to be a long process." He Hong said.
Why do haze days occur frequently
Why are haze days so frequent now? He Hong pointed out that firstly, the big background is that the urbanization rate has increased too quickly. The problem of air pollution in developed countries usually occurs when the urbanization rate is around 50%, and China's urbanization rate is also within this range, which is a major background.
He Hong said that haze occurs frequently, and there are external meteorological factors involved. However, what we value more is the internal factors of atmospheric composite pollution. Under the conditions of combined atmospheric pollution, the enhancement of atmospheric oxidation and the acceleration of the transformation from gaseous pollutants to particulate pollutants are the fundamental reasons for the frequent occurrence of haze events in the central and eastern regions of China. The amount of PM2.5 or PM10 and their precursor pollutants in the atmosphere greatly exceeds the environmental capacity formed by local climate, terrain, and other conditions. Once sustained calm weather occurs, pollutants cannot diffuse, leading to excessive fine particles in the atmosphere.
Why is haze difficult to control? "This is because typical compound pollution causes a decrease in the capacity of the atmospheric environment. In fact, there is no direct international experience to learn from, which is also one of the reasons why haze is difficult to control." He Hong said.
Three governance measures still need to be taken simultaneously
He Hong believes that in order to reduce the frequency of haze occurrence in China, it is necessary to strengthen control in four aspects in the near future, including motor vehicle emission control, coal-fired flue gas desulfurization and denitrification, control industrial exhaust gas pollution, reduce unorganized emissions from agriculture, animal husbandry, and biomass combustion.
"Among them, upgrading the quality of oil products and controlling motor vehicle exhaust pollution should be given priority. This is because motor vehicle exhaust directly emits PM2.5 and its precursors, which contribute significantly to the formation of atmospheric haze in urban areas. In addition, China's emission regulations for gasoline vehicles have not yet included restrictions on fine particulate matter, and efforts should be made to develop fine particulate matter control technologies for gasoline vehicles as soon as possible to support new standard legislation," He Hong said. "In terms of pollutant types, it is recommended to prioritize the control of nitrogen oxides, volatile organic compounds, and ammonia, as these pollutants are closely related to the formation of haze."
Experts also point out that pollution control requires regional participation and strong driving force from national policies and mechanisms.
