Visualizing Environmental Science

(Marvins-Underground-K-12) #1
Effects of Air Pollution 205

Dust dome

Rural City Rural

Wind
direction
Pollution
plume

a. A dust dome of pollutants forms over a city when the air is
somewhat calm and stable.


b. When wind speeds increase, the pollutants move downwind
from the city.


(the vertical motion of warmer air) lifts pol-
lutants into the air, where they remain be-
cause of the somewhat stable air masses the
urban heat island produces. If wind speeds
increase, the dust dome moves downwind
from the city, and the polluted air spreads
over rural areas (Figure 8.13b).
Urban heat islands affect local air currents and
weather conditions. Cities located in valleys or up-
wind of mountain ranges are particularly susceptible
to buildup of pollutants on low wind days. For exam-
ple, urban heat islands may increase the number of
thunderstorms over the city during summer months.
The uplift of warm air over the city produces a low-
pressure cell that draws in cooler air from the sur-
roundings. As the heated air rises, it cools, causing
water vapor to condense into clouds and produce
thunderstorms.


  1. What are some of the health effects of
    exposure to air pollution?

  2. What are urban heat islands? What are dust
    domes?


Urban heat islands also contribute to the
buildup of pollutants, especially particu-
late matter, in the form of dust domes over
cities (Figure 8.13a). Pollutants concen-
trate in a dust dome because convection


dust dome A dome
of heated air that sur-
rounds an urban area
and contains a lot of
air pollution.

Air temperature (°C) 86 Air temperature (°F)

88

90

92

31

32

33

34

30

Rural Suburban
residential

Commercial Downtown Urban
residential

Park Suburban
residential

Rural
farmland

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This figure shows how temperatures might vary on a summer afternoon. The city stands out as a heat
island against the surrounding rural areas.


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