Asian cities

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. 

The hydroxyl radical is central in tropospheric chemistry and photochemical smog formation. The hydroxyl radical OH is continually being formed and consumed in the troposphere and it has very short half-life due to its high reactivity, especially in urban polluted air. This species carries no charge, and is therefore chemically distinct from hydroxyl ion, OH , which has an additional electron. The major route for the formation of hydroxyl radical in the troposphere occurs by a complicated mechanism. 

Other sources of OH are shown in equations (5)-(7), and reaction (6) can give a peak in OH shortly after sunrise under some conditions of local air pollution 

The main two reactions of OH radical are connected with addition and abstraction of an H+ atom. 

Physical characteristics of photosmog include a yellow-brown haze, which reduces visibility, and the presence of substances which irritate the respiratory tract and cause eye-watering. The yellowish color is owed to NO2, whilst the irritant substances include ozone, aliphatic aldehydes, and organic nitrates. The four conditions necessary before photosmog can develop are  

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Figure 1. Ambient levels ofTSP in Asian cities (ESCAP, 2000).

In the wake of growing numbers of motor vehicles, the problem is likely to become more acute in the future. Many Asian cities within the more prosperous economics had already tripled or quadrupled in the number of passenger cars over the last 10-15 years. In Bangkok, for example, the number of road vehicles grew more than sevenfold between 1970 and 1990 and more than 300,000 new vehicles are added to the streets of this city every year. In China, it is projected that by 2015, there will be... 

Today, neither household nor office is conceivable without LCDs. They are flat, lightweight, low in energy consumption, and transportable, and continue to displace older technologies such as cathode ray tubes (CRT). After all, a flat television that hangs on the wall like a painting is highly desirable - especially in the living rooms of East Asian cities where space is often in short supply. In fact, surely an LCD TV would be better than a bulky TV set in any room anywhere ... 

Tropospheric ozone levels are increasing in many Asian cities as the principal products of photochemical smog formation. The main cause of this phenomenon is the rapid development of the transport system and the tremendous growth of the number of vehicles in all Asian countries. More details are given in Chapter 3. 

Thus this type of urban air pollution is called photochemical smog of Los Angeles type. This air pollution phenomenon is very frequent in many Asian cities, especially those in subtropical and tropical zone. 

The difference between the oxidation chemistry occurring in unpolluted background areas and that involved in photosmog formation in Asian cities, is that the latter condition occurs when the concentrations ofNOx and HC are much higher than in rural areas (Table 2). 

ROLE OF PARTICLES IN URBAN AIR POLLUTION IN ASIAN CITIES... 

A common process for the formation of aerosol mists involves the oxidation of SO2, which content is typically high in the urban air of most Asian cities (see Section 2) to H2SO4. This acid is a hydroscopic substance that attracts water vapor in the atmosphere to form small liquid droplets, as follows... 

We should remember that urban air in Asian cities like Bangkok, Beijing or Seoul contains basic compounds, such as ammonia from automobile emissions or calcium oxide from cement kiln and dust. In these conditions, sulfuric acid will react to form salts... 

The preceding examples show various ways in which solid or liquid inorganic particulates are formed in polluted urban air hy chemical reactions. Such reactions constitute the most important general processes for the formation of aerosols, particularly the smaller particles in air of Asian cities. 

Important environmental sources of sootparticles in Asian cities are burning coal, petroleum products, and wood. Coal burning produces large amounts of soot particles and still is an important source of reducing visibility in many cities of China and India. 

Visibility impairment in urban air is greatly affected by ambient particulate substances organics, soot (elemental carbon), soil dust, sulfates and nitrates. One of the primary particles, soot is emitted directly to urban air by diverse biomass burning, diesel engines and agricultural activities. All these process are greatly active in Asian cities. 

The reader can determine the sources of air pollution in his/her own city and estimate the type of smog, which is predominant during a year or separate seasons. However, we should note that in many Asian cities like Bangkok, New Delhi, Bombay, Jakarta, and Beijing, both types of smog are developing, and very often, simultaneously (ESCAP, 2000). 

Characterize the general sources of air pollution in the Asian cities. Compare the average data with those for your own city. 

Characterize the role of transport in urban air pollution in various Asian cities. Explain why two-wheeler engines emit more pollutants than car engines. 

Discuss the role of biomass fuel in indoor air quality in Asian cities. Give examples. 

Discuss the connection between urban air pollution and human health in Asian cities. Present examples of airborne diseases. 

Accounting for the high SPM concentration in many Asian cities, that drives the SO2 oxidation, heterogeneous oxidation of particles may predominant the process, especially under high urban pollution conditions. 

Present a discussion of chemical processes that lead to the damage of construction materials in Asian cities. 

Chlorine is the most commonly used disinfecting agent in the Asian cities. Other disinfectants are ozone, chlorine dioxide, and ultraviolet radiation. Some new disinfecting agents are now in advanced water treatment systems, like bactericides, surfactants, antibiotics, irradiation, sonification, and electric shock. 

The commonest of these occur in industrialized and urban areas where discharges from indnstry canse the snrface water (and groundwater to a lesser extent) to be contaminated with phenol or its derivatives, like cresol. Examples include the manufacture of certain herbicides or their precursors, the pulp and paper industry, the manufacture of phenol for use in plastics, such as phenol-formaldehyde, the manufacture and use of pentachlorophenol as a wood preservative, use of phenol derivatives (cresol, etc.) in hospitals, etc. The runoff of these compounds to surface waters and seepage to the groundwater are enlarged in rainy seasons in many Asian cities. 

We strongly recommend the nse of these filters for people staying in varions Asian cities, like Bangkok downtown, especially during the rainy season. 

Before leaving this sub-section on chlorine as a disinfectant, we should note that the majority of the Asian cities still do use chlorine to disinfect drinking water. The benefits in term of protection from water-borne diseases in Asia far overweigh the possible hazard from, for example, 10 or 20 ppb of trihalomethanes. Disinfection with chlorine may possibly pose a cancer risk in old age no disinfection in the Asian region does mean a substantial chance of dying from typhoid fever or cholera as a child or young adult. However, as we have seen in Table 1, there are different methods of disinfection and we consider some of these alternatives to chlorination. 

Hospital incineration yields predominantly octachlorodibenzo-/7-dioxin, and the very toxic TCDD amounts to only a few percent of the mixture (Bunce, 1994). More dioxin emission with high TEQ values is connected with open garbage burning that is often practiced in the Asian cities and uncontrolled landfills. 

In the Asian cities, municipal solid waste (MSW) is generated from residences, commerce, institutions, construction and demolition, cleaning services and treatment plants. Generation rates ofMSW vary from city to city and season to season. In most of the Asian cities, these rates range from less than 0.5 to 0.8 kg per capita per day. Some cities have higher generation rates of more than 1.0 kg per capita per day. 

The composition of MSW varies significantly from city to city. The compostable waste fraction represents typically more than 25% in most of the Asian cities, followed by non-compostable waste, paper and cardboard, and plastics, as shown in Figure 4. 

The amount of human waste in the MSW is significant in squatter areas of many Asian cities, like Hanoi, Calcutta, Dhaka, etc., where wrap and throw sanitation is common or bucket latrines are emptied into waste containers. 

The advantages of the activated sludge reactor in comparison with the trickling filter are related to the maintenance at the optimum temperature for biological activity and relatively small operational space. The first point is important for countries with moderate climate, like South Korea, Japan and partly China, whereas the second one, for many Asian cities (Hong Kong, Singapore, Seoul, etc.) where land is expensive. 

Recycling in developing countries relies largely on informal collection of materials from waste carried out by human scavengers or wastepickers. In the Asian cities, it has been estimated that up to 2% of the population survives by recovering materials from waste to sell for reuse or recycling or for their own consumption. 

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