Urban Air Pollution - Air Pollution and Global Warming: History, Science, and Solutions - page 84

Figure 4.9. Arie Haagen-Smit (1900-1977). Courtesy
the Archives, California Institute of Technology.

In 1952, Haagen-Smit discovered the mechanism of
ozone formation in smog. In the laboratory, he produced
ozone from oxides of nitrogen and reactive organic
gases in the presence of sunlight. He suggested that
ozone and these precursors were the main constituents
of Los Angeles photochemical smog.
On the discovery of the sources of ozone in smog, oil
companies and business leaders argued that the ozone

Figure 4.11. Photochemical smog in Los Angeles,
California, on July 23, 2000. The smog hides the
high-rise buildings in downtown Los Angeles and the
mountains in the background. Photo by Mark Z.
Jacobson.

originated from the stratosphere. Subsequent measure-
ments showed that ozone levels were low at nearby
Catalina Island, proving that ozone in Los Angeles was
local in origin.
Photochemical smog has persisted to this day in the
Los Angeles Basin (e.g., Figure 4.11). It has also been
observed in most cities of the world. Notable sites of
photochemical smog include Mexico City, Santiago,
Tokyo, Beijing, Calcutta, Johannesburg, and Athens.
Unlike London-type smog, photochemical smog does
not require smoke or fog for its production. Both
London-type and photochemical smog are exacerbated
by a strong temperature inversion (Section 3.3.1.1).
In the following sections, gas chemistry of back-
ground tropospheric air and photochemical smog are
discussed. Regulatory efforts to control smog since the
1940s are summarized in Chapter 8.

Figure 4.10. Smog damage to sugar beets. Courtesy
South Coast Air Quality Management District,
www.aqmd.gov.