C Pollution distribution and impacts

Polluted atmospheres often display well-marked physical features around urban areas that are very dependent upon environmental lapse rates, particularly the presence of temperature inversions, and on wind speed. A pollution dome develops as pollution accumulates under an inversion that forms the urban boundary layer (Figure 12.23A). A wind speed as low as 2 m s-1 is sufficient to displace the Cincinnati pollution dome downwind, and a wind speed of 3.5 m s-1 will disperse it into a plume. Figure 12.23B shows a section of an urban plume with the volume above the urban canopy of the building tops filled by buoyant mixing circulations. When an inversion lid prevents upward dispersion, but lapse conditions due to morning heating of the surface air allow convective plumes and associated downdrafts to bring pollution back to the surface, this process is termedfumigation. Downwind, lofting occurs above the temperature inversion at the top of the rural boundary layer, dispersing the pollution upwards. Figure 12.23C illustrates some features of a pollution plume up to 160 km downwind of St Louis on 18 July 1975. In view of the complexity of photochemical reactions, it is of note that ozone increases downwind due to photochemical reactions within the plume, but decreases over power plants as the result of other reactions with the emissions. This plume was observed to stretch for a total distance of240 km, but under conditions of an intense pollution source, steady large-scale surface airflow and vertical atmospheric stability, pollution plumes may extend downwind for hundreds of kilometres. Plumes originating in the Chicago-Gary conurbation have been

Plume Lofting

Figure 12.23 Configurations of urban pollution. (A) Urban pollution dome. (B) Urban pollution plume in a stable situation (i.e. early morning following a clear night). Fanning is indicative of vertical atmospheric stability. (C) Pollution plume northeast of St Louis, Missouri, on 18 July 1975.

Sources: (B) After Oke (1978); (C) After White et al. (1976) and Oke (l978).

Figure 12.23 Configurations of urban pollution. (A) Urban pollution dome. (B) Urban pollution plume in a stable situation (i.e. early morning following a clear night). Fanning is indicative of vertical atmospheric stability. (C) Pollution plume northeast of St Louis, Missouri, on 18 July 1975.

Sources: (B) After Oke (1978); (C) After White et al. (1976) and Oke (l978).

observed from high-flying aircraft to extend almost to Washington, DC, 950 km away.

The impacts of air pollution include: direct meteorological effects (on radiative transfer, sunshine, visibility, fog and cloud development), greenhouse gas production (by release of CO2, CH4, NO^ , CFCs and HFCs), photochemical effects (tropospheric ozone formation), acidification (processes involving SO2, NO^ and NH3), and societal nuisance (dust, odour, smog) affecting health and the quality of life especially in urban areas.

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Responses

  • Libera
    Why do plumes extend downwind?
    9 years ago
  • Pupetta
    What is pollution dome and pollution plume?
    9 years ago
  • Aziza
    What is a polluton dome?
    8 years ago

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