Environment and Health Series (11) - The impact of overhead source plumes on the surface ecological environment

? The polluted air masses emitted by elevated chimneys (generally more than 200 meters above the ground) spread to the ground. This process is called smoke, which will cause a serious decline in air quality in downwind areas [1] . The continuous smoking of high-altitude plumes occurs in a strongly adiabatic environment, which requires the existence of a thermal inner boundary layer (TIBL). Smoking occurs when the plume is discharged into a shallow layer of unstable air while the upper layer is covered by a deep layer of stable air. This situation generally occurs in cloudy weather in spring [2] . Both the neutral atmosphere (the potential temperature remains unchanged in the vertical direction) and the stable air mass (the potential temperature increases with the height) will cause smoke in the downwind area. It is different from whether the smoke plume is transmitted in the neutral atmosphere or in the downwind area. It is carried out in the stable atmosphere above the neutral atmosphere, and the latter smokes more slowly [3]. Unstable air masses whose potential temperature decreases with increasing altitude generally occur in strong convective weather with less frequency. At this time, the plume diffusion direction is relatively disordered and there is no fixed downwind area.

? In cloudless or less cloudy weather, the removal of sulfur dioxide (SO 2 ) in the smoke plume is mainly through the reaction with OH radicals during the day, while the removal of nitrogen oxides (NO x ) is during the day. It occurs during the day and night, and is removed by rapid reaction with OH radicals during the day and by reaction with NO 3 /N 2 O 5 at night. Therefore, in cloudless weather, the removal efficiency of NO x is more than 10 times that of SO 2 . In cloudy weather, generally after several days of clear sky illumination, the removal of SO 2 is mainly through liquid phase chemical reaction, and photochemical reaction is not important, but NO x will not be contained in the droplets. Remove. For gases in the plume, the dry deposition rate of SO 2 is greater than NO x , while for liquid phase particulate matter, the dry deposition rate of nitrate is greater than that of sulfate [4] . So sulfur dioxide gas and nitrates diffuse more easily to the ground.

? The downwind transmission of smoke plumes will cause nearby residential areas to be polluted by particulate matter, causing the concentration of harmful substances such as benzopyrene to often exceed standards. During an airship survey in Europe, researchers detected ultrafine particles emitted by the metallurgical industry and measured the concentration of ultrafine particles with diameters less than 100 nanometers (3.2×10 5 /cm 3 ) in the smoke plume. When the wind speed is greater than 1 m/s, the ultrafine particle concentration observed on the ground in the downwind residential area is 1.4×10 5 particles/cm 3 , the SO 2 concentration is 88 ppb, and the CO concentration is 11 ppm. In these smoke polluted air masses, most of the ultrafine particles have a diameter of 19-44 nm, and the content of polycyclic aromatic hydrocarbons/benzopyrene is as high as 43.8/3.5 mg/g. Electron microscopy shows that most of the ultrafine particles in these plumes are pellets with a diameter of 30-50 nanometers, and polycyclic aromatic hydrocarbons are highly combined with the parent particles and are easily inhaled and permanently deposited in the human alveoli [5].

? In addition to the dry deposition process of overhead source plume aerosols that will lead to a decrease in air quality, the wet deposition process caused by the cloud process will also affect the surface water environment and soil environment. For example, black rain or red rain may occur near industrial areas [6] . Black rain refers to rain with black raindrops. It is mainly caused by black sand and dust in rainwater or suspended solids containing black metals such as iron ore elements. It has appeared in Guangxi, Hunan, Jiangxi and other places. Red rain refers to rain in which the raindrops are blood-red, caused by the rain containing red dust or phytoplankton rich in iron oxide (the monsoon transport path is farther over the sea). When red rain appears, there is a layer of red gray under the clouds. After the rain, the ground was covered with a thin layer of red dust. The raindrops falling on the clothes were stained yellow-red, like rust. France, Spain, Italy, and Türkiye have all seen red rain.

References

[1] Luhar A K. The influence of vertical wind direction shear on dispersion in the convective boundary layer, and its incorporation in coastal fumigation models[J]. Boundary -Layer Meteorology, 2002, 102(1): 1-38.

[2] Lyons W A, Cole H S. Fumigation and Plume Trapping on the Shores of Lake Michigan During Stable Onshore Flow[J]. Journal of Applied Meteorology, 1973, 12(3): 494-510.

[3] Luhar A K, Young S A. Dispersion moments of fumigating plumes–lidar estimates and PDF model simulations[J]. Boundary -Layer Meteorology, 2002, 104(3): 411-444.

[4] Hewitt C N. The atmospheric chemistry of sulfur and nitrogen in power station plumes[J]. Atmospheric Environment, 2001, 35 (7): 1155-1170.

[5] Leoni C, Hovorka J, Do?ekalová V, et al. Source Impact Determination using Airborne and Ground Measurements of Industrial Plumes[J]. Environmental Science & Technology, 2016, 50(18): 9881-9888.

[6] Editorial Board of "Dictionary of Atmospheric Science". Dictionary of Atmospheric Science[M]. 1994.