Atmosphere polluted urban

As mentioned in the previous section, the increased number of nuclei in polluted urban atmospheres can cause dense persistent fogs due to the many small droplets formed. Fog formation is very dependent on humidity and, in some situations, humidity is increased by release of moisture from industrial processes. Low atmospheric moisture content can also occur, especicilly in urban areas two causes are lack of vegetation and rapid runoff of rainwater through storm sewers. Also, slightly higher temperatures in urban areas lower the relative humidity. 

The nutrition needs of the future will be met with more limitations than in the past on the use of energy and restrictions on contamination of the environment. The maintenance of natural resources will receive much more attention than in the past. Concerns will increase regarding desertification, deforestation, urbanization, salinification, soil and water degradation, and atmospheric pollution. There is considerable difficulty in delineating these limitations, particularly as one considers the responsibilities and interests of developed and developing countries. The role of economics offers an additional challenge in working out these relationships. 

Munier, I., Lefevre, R., Geotti-Bianchini, F. and Verita, M. (2002). Influence of polluted urban atmosphere on the weathering of low durability glasses. Glass Technology 43 225-237. 

The late 1970 s saw the birth of a new aspect of atmospheric chemistry. Thus, in addition to ozone and photochemical oxidant formed in the daytime photooxidation of VOCs, there is an important nighttime chemistry, not only in polluted urban and suburban air environments, but also in relatively remote atmospheres. 

FIGURE 1.5 Predicted rates of generation of OH/H02 in a polluted urban atmosphere as a function of time of day for three free radical sources (adapted from Winer, 1985). 

A major advantage of infrared absorption spectroscopy derives from the characteristic fingerprints associated with infrared-active molecules. On the other hand, interferences from common atmospheric components such as C02 and HzO are significant, so that the sensitivity and detection limits that can be obtained are useful primarily for polluted urban air situations. For atmospheric work, long optical path lengths are needed. 

Figure 11.3 shows typical ambient air spectra in two regions in which HNO-, (Fig. 11.3a) and NH-, (Fig. 11.3b), respectively, have characteristic absorption bands (Biermann et al., 1988). Figure 11.4 shows, for comparison, some typical reference spectra for HN03 and NH-, taken at much higher concentrations in a 25-cm-long cell (see Problem 6). It can be seen that the absorption bands in air even in a polluted urban area are relatively weak. However, FTIR has also proven particularly useful as a standard for intercomparison studies in polluted urban atmospheres (e.g., see Hering et al., 1988). 

These studies were carried out in a polluted urban atmosphere where the concentrations are relatively high it might be expected that the agreement (or lack thereof) would certainly not improve at the much smaller concentrations found in rural and remote regions. Similar disagreements have been observed in other intercomparison studies (e.g., Anlauf et al., 1985 Gregory et al., 1990b Huebert et al., 1990), even in synthetic atmospheres (e.g., Fox et al., 1988). 

A third issue is illustrated by the mass spectrum in Fig. 11.71a, which, as described by Murphy and Thomson (1997a), appears to have a peak at almost every mass. Thus, in many instances in the atmosphere, particularly in polluted urban areas, the spectra may be so complex that only major classes of compounds may be discernible. 

The concept of OH reactivity has been applied to give a first-cut assessment of the contribution of various individual organics and sources to photochemical oxidant formation in a number of situations. For example, Chameides et al. (1992) scaled the contribution of various VOC concentrations in a variety of atmospheres from remote to polluted urban areas using OH reactivity. They concluded that while NOx concentrations decreased from polluted urban areas to rural to remote regions, the total VOC reactivity assessed in this manner was comparable at all continental areas from remote to polluted. 

The potential hazard lies in its significant contribution to atmospheric pollution in general, especially in urban areas, and its resultant long term, low level exposures. 

In polluted urban atmospheres, singlet molecular oxygen may play an essential part in the oxidation of nitric oxide to nitrogen dioxide.5,6 The... 

Singlet molecular oxygen is of interest in connection with atmospheric chemistry with respect both to its mode of excitation and to the consequences of its presence in the upper or lower atmosphere. The first part of this section deals with processes of importance in normal, unpolluted atmospheres, while the second part examines the possibility, only recently appreciated, that singlet molecular oxygen may play a part in the chemistry of polluted urban atmospheres. 

Abstract Gaseous and particulate emissions from vehicles represent a major source of atmospheric pollution in cities. Recent research shows evidence of, along with the primary emissions from motor exhaust, important contributions from secondary (due to traffic-related organic/inorganic gaseous precursors) and primary particles due to wear and resuspension processes. Besides new and more effective (for NO emissions) technologies, non-technological measures from local authorities are needed to improve urban air quality in Europe. 

From an emission point of view, in spite of the constant technical developments of less pollutant vehicles and the implementation of diverse mitigation strategies for PM [31], atmospheric pollution by road traffic has not diminished for pollutants such as N02. Also it has to be highlighted the poor understanding of the so-called non-exhaust emissions as a major source of urban PM. Several studies have shown that the importance of these non-exhaust emissions is comparable (or even higher) to that of emissions from vehicle exhaust systems [3, 32-34] (Fig. 2). 

Airborne nanoparticles empirically fit well to log normal distributions and exhibit bimodal distributions in atmospheric urban environments. These arise from both natural and anthropogenic sources. Road vehicles remain a dominant source, contributing up to 90% of total PNCs, in polluted urban environments. 

Ozone (O3) is a bluish irritant gas that occurs normally in the earth s atmosphere, where it is an important absorbent of ultraviolet light. In the workplace, it can occur around high-voltage electrical equipment and around ozone-producing devices used for air and water purification. It is also an important oxidant found in polluted urban air. The effect of low ambient levels of ozone on admission to Ontario, Canada, hospitals for respiratory problems revealed a near-linear gradient between exposure (1-hour level, 20-100 ppb) and response. See Table 57-1 for 1999-2000 threshold limit values. 

Ozone is a major atmospheric pollutant in urban areas. In addition to its damaging effect on lung tissue and even on exposed skin surfaces, ozone attacks the rubber of tires, causing them to become brittle and crack. But in the stratosphere, where ozone absorbs much of the short-wavelength UV radiation from the sun, it provides a vital protective shield for life forms on earth. 

Photolysis of atmospheric pollutants by solar radiation results in an increase of ozone concentration in certain urban areas and is the cause of a sequence of oxidation reactions with polymers. Ozone reacts with practically all organic materials especially with alkenes. The rate of its reaction with alkene is several orders of magnitude higher than that with alkane. The ratio of the rate constants of ozone with ethene/ethane is 1.5 x 105, with propene/propane 1.6 x 106, and with butene- 1/butane 1.1 x 106, at room temperature [5],... 

Although only 10% of atmospheric ozone resides in the troposphere (0-15 km altitude) it has a profound impact on tropospheric chemistry. Ozone concentrations in the troposphere vary from typically 20-40 ppb for a remote pristine site to 100-200 ppb in a highly polluted urban environment. Ozone is a reactive molecule, which readily adds to carbon-carbon double bonds [8]. Reaction with ozone provides an important removal mechanism for many unsaturated reactive organic compounds. 

In addition to OH radicals, unsaturated bonds are reactive towards O3 and NO3 radicals and reaction with these species is an important atmospheric degradation mechanism for unsaturated compounds. Table 4 lists rate constants for the reactions of 03 and NO3 radicals with selected alkenes and acetylene. To place such rate constants into perspective we need to consider the typical ambient atmospheric concentrations of O3 and NO3 radicals. Typical ozone concentrations in pristine environments are 20-40 ppb while concentrations in the range 100-200 ppb are experienced in polluted air. The ambient concentration of NO3 is limited by the availability of NO sources. In remote marine environments the NO levels are extremely low (a few ppt) and NO3 radicals do not play an important role in atmospheric chemistry. In continental and urban areas the NO levels are much higher (up to several hundred ppb in polluted urban areas) and NO3 radicals can build up to 5-100 ppt at night (N03 radicals are photolyzed rapidly and are not present in appreciable amounts during the day). For the purposes of the present discussion we have calculated the atmospheric lifetimes of selected unsaturated compounds in Table 4 in the presence of 100 ppb (2.5 x 1012 cm 3) of O3 and 10 ppt (2.5 x 108 cnr3) of NO3. Lifetimes in other environments can be evaluated by appropriate scaling of the data in Table 4. As seen from Table 4, the more reactive unsaturated compounds have lifetimes with respect to reaction with O3 and NO3 radicals of only a few minutes ... 

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