In some cities in our country, hazy days account for almost half of the entire year

Thread Content

This post was last edited by wuhannrd on 2011-12-20 at 17:01. Why is foggy weather increasing? Flights are frequently delayed, masks have become bestsellers, and those who enjoy exercising in the morning are forced to stay at home... Recently, foggy weather has frequently affected various regions across China, from Guangzhou and Hangzhou in the south to Beijing and Lanzhou in the north. Monitoring data from the **Climate Center of the China Meteorological Administration** show that since September 1 this year, foggy weather has occurred frequently in the central and eastern regions of China; a total of 12 large-scale foggy weather events have taken place. Not only were there many days with fog, but its impact also covered a wide area. Autumn and winter are the seasons when fog is most common. Certain weather conditions facilitate the formation of fog, while pollutant emissions lead to an increase in particle concentrations. According to Zhao Shanshan, a senior engineer at the Climate Assessment Office of the **Climate Center, autumn and winter are the periods with the highest incidence of fog. **Analyses by the Climate Center indicate that specific meteorological conditions are a major cause of the frequent foggy weather in recent times. Since September, there has been less cold air activity affecting the central and eastern regions of our country, and this cold air is relatively weak; ground wind speeds are low, which facilitates the accumulation of water vapor in the lower layers of the atmosphere, thus contributing to the formation of fog ； Furthermore, the stronger activity of warm and humid air on the southern side of the Tibetan Plateau leads to highly active transport of southwestward warm and humid air currents originating from the Indian Ocean. These currents carry abundant moisture along a southwestward path to the central and eastern regions of China, reaching areas near Beijing as well; this increases the humidity in those regions significantly. It also facilitates the formation of low-level inversions, which is very conducive to the development of foggy weather. Experts point out that in addition to weather conditions, the increase in concentrations of particulate matter in the atmosphere – including coarse particles PM10 and fine particles PM2.5 – caused by industrial production, vehicle exhaust emissions, and coal burning for winter heating, are important factors contributing to fog and haze. At present, the pollutant emission levels in many cities have reached a critical point; they are highly sensitive to weather conditions. Air quality can meet the standards when dispersion conditions are favorable, but once unfavorable weather conditions arise, air quality and visibility drop rapidly. There is a significant upward trend in the number of haze days in the central and eastern regions. At present, in some large cities, the number of haze days accounts for over 30% of the total number of days in a year, with some cities even seeing around half of their days affected by haze. In fact, there is a difference between ‘fog’ and ‘haze’. ”**Sun Leng, a senior engineer at the Climate System Monitoring Laboratory of the Climate Center, explained that fog is a weather phenomenon that occurs when water vapor suspended in the atmosphere condenses, resulting in visibility below 1 kilometer ； The formation of haze is primarily the result of a large number of particles suspended in the air, combined with weather conditions. There are three causes for this: an increase in calm wind conditions in the horizontal direction. As buildings in cities become taller, the effects of obstruction and friction cause air currents to weaken significantly as they pass through urban areas. The increase in calm wind conditions is not conducive to the dispersion and dilution of airborne particles, allowing them to accumulate easily in urban areas and their surrounding suburbs ； ——An inversion has occurred in the vertical direction. An inversion layer is like a lid covering the city; this phenomenon, in which the temperature at higher altitudes is higher than that at lower levels, restricts the vertical movement of air in the lower layers of the atmosphere. As a result, airborne particles are unable to rise to higher altitudes and remain trapped in the lower layers near the ground. ——An increase in suspended particulate matter in the air. With the growth of urban populations and industrial development, as well as the sharp increase in motor vehicles, pollutant emissions and suspended particles have risen significantly, directly leading to reduced visibility. “When these conditions for the formation of haze occur, they also result in a large amount of dust, smoke particles, and other condensation nuclei in the air; water droplets can easily condense on these particles, leading to fog, which does not dissipate easily due to wind. ”Sun Leng said, “Therefore, fog and haze often occur together.” ” **Monitoring by the Climate Center shows that, from 1961 to 2010, the average annual number of hazy days across the country showed a significant increasing trend. Since the beginning of this century, the number of haze days across the country has increased significantly, with a notable rise in such days in the central and eastern regions. According to the latest statistics from environmental protection agencies, in some large cities, the number of days with haze now accounts for over 30% of the total number of days in a year; in some cases, it even reaches around half of the total days in a year. Human emissions are closely related to hazy weather; PM2.5 has a greater ability to reduce air visibility, and its main source is human emissions. Environmental experts point out that suspended particles in the air are invisible to the naked eye, but they can reduce air visibility and lead to hazy conditions. Particulates of different sizes in the air can all reduce visibility. However, compared to larger particles, fine particulates (PM2.5) have a greater ability to reduce visibility, and they are the main cause of reduced visibility on hazy days. The reporter learned from the China National Environmental Monitoring Center that the monitoring results for haze in the pilot cities in 2010 showed that during haze episodes, the concentrations of PM10 and PM2.5 increased significantly. Moreover, there was a clear negative correlation between fine particles and visibility – the higher the level of fine particles, the lower the visibility ； Lower levels of fine particles result in higher visibility), which indicates that haze conditions are closely related to particle concentration; an increase in particle concentration is one of the key factors contributing to haze, in addition to meteorological conditions. Tan Zhihuan, a Ph.D. in environmental science, explained that the main source of PM2.5 is human emissions. Humans emit both PM2.5 directly and certain gaseous pollutants, which transform into PM2.5 in the air. Direct emissions mainly come from combustion processes, such as the burning of fossil fuels (coal, gasoline, diesel), the burning of biomass (straw, firewood), and waste incineration. The gaseous pollutants that convert into PM2.5 in the air are mainly sulfur dioxide, nitrogen oxides, ammonia, and volatile organic compounds. Other human-induced sources include: road dust, construction dust, industrial dust, etc. Fine particulate matter PM2.5 in the atmosphere often carries pollutants such as sulfides, nitrogen oxides, and heavy metal particles, which are mostly emitted by industrial sources; as a result, it causes significant harm to the human body.