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95 The way chemists understand urban air pollution and how they relate this understanding to policymakers underwent great transformations in the twentieth century. These changes cannot be simplified to notions such as: “pollution got worse,” because in many cities the concentrations of aggressive primary pollutants such as fly ash, smoke, and sulfur dioxide actually declined very substantially. The last, for example, decreased by more than an order of magnitude in some cities during the last half of the century, largely because coal was no longer burned in large quantities.1 Changes in fuel sources—for example, from coal to petroleum—refocused pollution concerns from primary pollutants, like ash or smoke, to a more complex problem, that of the formation of photochemical smog. Nor can we glibly say that “chemists got smarter,” for even as increasingly sophisticated scientific accounts emerged, it was the complex, nonlinear chemistry that failed to translate easily into policy recommendations for air quality or emissions standards. Understanding Los Angeles smog was critical to forging the modern discipline of atmospheric chemistry. The way a variety of chemists and atmo5 DECIPHERING THE CHEMISTRY OF LOS ANGELES SMOG, 1945–1995 Peter Brimblecombe 96–––Peter Brimblecombe spheric scientists produced accounts of complex chemical reactions proved to be a mode of scientific development. Understandings of the LA smog have had far-reaching effects, well beyond petroleum-related pollution and beyond scientific inputs to policy debates. Without a history of the science behind an increasingly complex model of smog formation improvements in the air over LA and around, these developments cannot be properly understood. Origins of Los Angeles Smog The word “smog”—derived from the words “smoke” plus “fog”—was first coined by physician Henry Antoine des Voeux in 1905 in a paper that described pollution in British coal-burning cities. The term “smog” was used to describe several episodes in the early twentieth century where a smokelike substance in the air not only compromised visibility but also caused a variety of adverse health effects. The most notable of these pre–World War II smogs was the St. Louis smog of 1939, where an inversion layer trapped thick smoke for over a week; streetlights were left on during the day to improve visibility. A few years later, during WWII, there were several episodes of severe air pollution in the city of Los Angeles; local residents referred to these as smogs. At the time some feared the pollution was the result of Japanese gas attacks; others thought it important not to reduce the output of strategic industry by imposing smoke control measures. Air pollution episodes were occasionally so bad in Los Angeles in the early 1940s that spectators in the stands could not see baseball games. However, the war effort did not obscure all local concerns; there were also worries about the health impacts of smog on Los Angeles residents in the summer of 1943.2 Even in the 1940s there was an awareness of its smog’s “peculiar nature” and the differences between it and smoke. Ironically, the term “smog” may have obscured the true picture, but this subtlety was lost on city authorities who set up a Bureau of Smoke Control in the health department in 1945. After the war the Los Angeles Times brought air pollution expert Raymond R. Tucker from St. Louis to examine the smog problem and make recommendations. Tucker was a mechanical engineering professor at Washington University and the City Smoke Commissioner from 1934–37. He was credited with an accurate analysis and solution to the smog episode in St. Louis in 1939, and he would later rise to become mayor of the city. Tucker’s Los Angeles Times report in 1946 about smog reinforced the notion that it was not just a few smokestacks causing the problem but a plethora of uncontrolled sources, including backyard rubbish incinerators and smoking Deciphering the Chemistry of Los Angeles Smog, 1945–1995–––97 trucks. However, Tucker’s St. Louis experience was misleading in his investigation of LA smog. The air pollution in St. Louis derived from coal smoke, so it had few similarities with the photo-oxidative smogs of Los Angeles. Tucker’s report recommended establishing unified air pollution control districts at the county level. On April 15, 1947, despite stiff opposition from industry , these recommendations became a reality. Tucker’s report did not single out the automobile as a source of LA’s smog. He noted the presence of sulfur dioxide in the smog, but argued that the lack of...

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