Experimental study of small-scale particles in atmospheric brown clouds

1317 In this paper we present the results of the experi� mental study of atmospheric brown clouds (ABC), which are congestions of polluted air on a regional scale consisting of large amounts of smallscale parti� cles of soot, sulfates, nitrates, soot dust, and other types of pollution (1, 2). The object of our research is smallscale particles that comprise the ABC of the Central Asia region, which were collected on the terri� tory of the highmountainous lidar complex Teplokly� uchenka belonging to the Kyrgyz-Russian Slavic University in the Central Tien Shan and at the Scien� tific Station of the Russian Academy of Sciences in Bishkek (SS RAS). The particles studied are charac� terized as nanoparticles (sizes from 1 to 1000 nm) and microparticles (size 1-1000 µm), which allows us to use the classification of particles based on their sizes. The nanoand microscale particles effectively influ� ence the screening of solar irradiance and scattering of the light in the atmosphere causing a decrease in visi� bility and disturbing the climatic balance (3). The brown shade of the ABC is caused by absorp� tion and scattering of the solar irradiance by the anthropogenic black carbon, soot dust, soil particles, and nitrogen dioxide. The atmospheric brown clouds are formed from anthropogenic and natural pollut� ants. At present, the developing countries of Asia, Africa, and South America suffer most of all from the pollutants released into the atmosphere, and black carbon, in particular. The most critical state is recorded in the Asian countries, in which the brown gas is especially dense. It spreads widely during the long dry season. Owing to this fact, the population of the region, in which more than 50% of the world pop� ulation lives, suffers from the negative influence of the brown gas on the health, hydrological cycle, and agri� culture (2). If we additionally take into account the role of the water and hydroenergetic resources in the formation of the economy of the Central Asian region, the problem of possible effects related to the ABC is one of the main strategic components of the national security of countries in this region (4). Despite the fact that the term "atmospheric brown clouds" became widely accepted only in the beginning of the 21st century, this phenomenon (without using this term) was actually noted already in September 1989 in the southwestern part of Tajikistan during a joint expedition of Soviet and American scientists (see, for example, (5-10)). In particular, they obtained results on the distribution of dust aerosol by size in the deserts of Central Asia (6) and demonstrated the significant role of the absorption of radiation in the optical range by black carbon during the formation of the radiation regime in the atmosphere (10). The influence of ABC on climate is particularly related to the incomparably greater efficiency of smallscale soot particles in the radiation processes than carbon dioxide, which is associated with an espe� cially important role in climatology. This is caused by the fact that absorption of radiation by smallscale soot particles is characterized by low selectivity. It is related to the entire wide range of solar irradiance but not to the narrow band of absorption by carbon diox� ide. It takes place (11) even if the concentration of crystal carbon in the atmosphere is only a few mil� lionths of the gaseous form of carbon dioxide and the productivity of its formation processes is significantly smaller than the productivity of carbon dioxide sources.