Urban atmosphere background

These calculations indicate that for background conditions the accumulation mode is a larger contributor to light scattering than the coarse mode but that the coarse mode is a non-negligible component of the scattering coefficient. This situation contrasts with that of polluted urban atmospheres in which the accumulation mode is responsible for more than 90% of the total scattering coefficient. 

Fig. 5. Size distributions of atmospheric particles ia (—) urban, (------) mral, and (------) remote background areas.

Yin J, Harrison RM, Chen Q, Rutter A, Schauer JJ (2010) Source apportionment of fine particles at urban background and rural sites in the UK atmosphere. Atmos Environ 44 (6) 841-851... 

Heal, M.R., Hibbs, L.R., Agius, R.M. and Beverland, I.J. (2005) Total and water-soluble trace metal content of urban background PM 10, PM2.5 and black smoke in Edinburgh, UK. Atmospheric Environment, 39(8), 1417-30. 

The basic chemistry responsible for urban photochemistry is essentially the same as that takes place in the unpolluted atmosphere (see Section 2.5). It is the range and concentrations of NMHC fuels and the concentrations of NO coupled to the addition of some photochemical accelerants that can lead to the excesses of urban chemistry. For example, in the Los Angeles basin it is estimated that 3333 ton day of organic compounds are emitted as well as 890 ton day of NO - In addition, to the reactions forming OH in the background troposphere, i.e. via the reaction of 0( D) with H2O, viz... 

Trichloroethane has been identified in urban, rural, and indoor air throughout the United States at concentrations shown in Table 5-3. Due to the nature of 1,1,1-trichloroethane s use, volatilization to the atmosphere is a predictable outcome, and thus its widespread detection is not unexpected. It is the only chlorinated ethane regularly seen as a background pollutant in the troposphere (Spence and Hanst 1978). For the year 1980, an estimated global atmospheric quantity of... 

Particle size and surface area as well as vertical distribution are also important for heterogeneous reactions. The majority of the mass of atmospheric aerosol matter is represented by particles of size 10 -10 m [5], i.e. their surface area must be 10 m g. The specific surface area A of solid aerosols near the Earth surface is considered to be 10 m dm of air under background conditions and can increase by a factor of 100 in urban areas [3]. The vertical distribution of A is shown in Fig. 1(B). Due to sedimentation, almost all of aerosols are located in the lower layer of the troposphere. 

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