Visualizing Environmental Science

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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