Photochemical smog/particulates

Combustion processes are the most important source of air pollutants. Normal products of complete combustion of fossil fuel, e.g. coal, oil or natural gas, are carbon dioxide, water vapour and nitrogen. However, traces of sulphur and incomplete combustion result in emissions of carbon monoxide, sulphur oxides, oxides of nitrogen, unburned hydrocarbons and particulates. These are primary pollutants . Some may take part in reactions in the atmosphere producing secondary pollutants , e.g. photochemical smogs and acid mists. Escaping gas, or vapour, may... 

Photochemical smog comprises mixtures of particulate matter and noxious gases, similar to those that occurred in the typical London-type pea-soup smog. The London smog was a mixture of particulates and oxides of sulfur, chiefly sulfur dioxide. But the overall system in the London smog was... 

There is no commercially available instrument for the continuous monitoring of any of the chemical species present in the particulate component of photochemical smog. Methods should be developed for the direct and continuous measurement of such species. Species of interest include sulfates, nitrates, some oxygenated organic compounds, and lead. 

Photochemical air pollution is characterized by the formation of a so-called "photochemical oxidant" and the reduction of visibility due to the simultaneous production of aerosol particles or particulates. This type of air pollution is commonly known as "photochemical smog. ... 

The American 1970 Clean Air Act defined ambient air quality standards (NAAQS) in the United States for atmospheric ozone, NO, lead, carbon monoxide, sulfur oxides, and PM-10 (particulate matter less than 10 p.m). The strategy to reduce levels of lead, NOx, PM-10, and to some extent carbon monoxide was to control emissions from automobiles that included the phasing-out of leaded fuel. As previously noted, ozone is a product of the photochemical reaction of volatile organic compounds with NOx (photochemical smog), so the balance between organic compounds and NOx pollutants is important in meeting target ozone levels (e.g., 0.12 ppm). Emissions from stationary sources is an important factor, and limits have been set for them. Because of low pressure drop requirements, coated monolithic catalysts... 

Recognition of particulate matter (4) heterogeneous atmospheric chemistry (1) photochemical modeling understanding mechanisms of photochemical smog formation (2) rise and fall of CFCs global warming ozone depletion (3)... 

The above mentioned urban air pollution in Asian cities drives the tropospheric chemical reactions. This tropospheric chemistry is dominated by the oxidation of trace atmospheric components, as aresult ofwhich organic compounds such as methane and other hydrocarbons are converted into carbon dioxide and water. The consequences of these chemical transformations are known as photochemical smog (photosmog) and the associated problem of ground level ozone. Here we should consider also the effects of particulate matter, one of the major pollutants of urban air in Asia. 

Here we should compare the visibility decrease due to particulates concentration in urban air, so called London smog, with a similar atmospheric phenomenon, Los Angeles photochemical smog. 

Air pollution occurs when the concentration of natural and/or man-made substances in the atmosphere becomes excessive and the air becomes toxic. Emissions from transportation, industry, and agriculture are man-made sources of air pollution. Primary pollutants are gases, liquids, and particulates dispersed into the atmosphere through either man-made or natural processes. In the United States, the primary pollutants are carbon monoxide, sulfur dioxide, nitrogen oxides, volatile organic compounds (VOCs), and particulate matter (soot, dust, etc.). Secondary pollutants are derived from primary pollutants that undergo a chemical reaction and become a different type of toxic material. In the United States, secondary pollutants are ozone, photochemical smog, and acid rain. 

In the twentieth century, dense smoke emission was gradually brought under control, and emphasis shifted to control of photochemical smog (i.e., control of hydrocarbon and oxide of nitrogen emissions from motor vehicles and stationary sources), of particulate matter and sulfur oxide emissions, of toxic and hazardous emissions (e.g., lead, mercury, beryllium, vinyl chloride, and asbestos), and acidic deposition. ... 

Also characteristic ate the particulate secondary pollutants sulfate and nitrate, the latter being especially associated with photochemical smog processes. Nitrate formation during daytime occurs through reaction of nitrogen dioxide with the hydroxyl radical, with subsequent neutralization of nitric acid vapor by ammonia to form ammonium nitrate (NH4NO3) particles, which equilibrate with their gas-phase precursors and are termed semivolatile ... 

Polluted air, e.g., particulate matter, sulfur dioxide, nifrogen dioxide, hydrogen sulfide, and photochemical smog [31]. 

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