Geoscience Reference
In-Depth Information
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rays can set off reactions that produce various
additional VOCs and aldehydes. These chemically
complex summer smogs are associated with
asthma and various bronchial complaints. Cities
such as Los Angeles, Mexico City, Teheran and
Athens are particularly prone to incidents of
photochemical smogs because they combine high
car-use levels with warm climates and landscapes
that actively contribute to the trapping of air
pollution (McNeill, 2000: 72).
Los Angeles's location plays a crucial role in the development of photochemical smogs in the city.
Its coastal location often means that onshore breezes return the city's air pollution to the metropolis
as part of a cooler air mass
(Plate 3.3).
The cooler air mass pushes the warmer air it encounters in
the city upwards. This process results in what meteorologists term an inversion layer. This
inversion layer acts like a blanket trapping air pollution at low altitudes. Given that Los Angeles is
surrounded by mountains, inversion layers can become very difficult to break when they settle over
the urban region. These relatively stable atmospheric conditions provide time for the sunlight to
stimulate chemical reactions at low altitudes within the city and the production of photochemical
smogs.
Key reading
McNeill, J. (2000) Something New Under the Sun: An Environmental History of the Twentieth Century, Penguin,
London: 72-76
