Contaminacion atmosferica

Clearing the Air in Los Angeles
Although Los Angeles has the most polluted skies in the nation, it is one of the few cities where air quality has improved in recent decades
by James M. Lents and William J. Kelly

O

n some hot, sunny days, the 14 million residents of the Los Angeles area inhale a thick, brownish-gray haze, and no one can ignore its eÝect. The smog obscures the SanBernardino Mountains and the warm California sun; it irritates the eyes and nose; it restricts the activities of athletes and people who have breathing disorders; it injures the lungs of both young and old. Southern CaliforniaÕs air quality is the worst in the U.S. Air pollution in the region reaches unhealthful levels on half the days each year, and it violates four of the six federal standards forhealthful airÑthose for ozone, Þne particulates, carbon monoxide and nitrogen dioxide. In 1991 the South Coast Air Basin exceeded one or more federal health standards on 184 days. Yet these statistics hide a remark-

JAMES M. LENTS and WILLIAM J. KELLY work together at the South Coast Air Quality Management District ( AQMD ), the regional air-pollution control agency for the Greater Los Angeles area.Before becoming executive oÛcer of AQMD in 1986, Lents headed the air-pollution control program for the state of Colorado. In 1970 he received a Ph.D. in physics from the Space Institute at the University of Tennessee. Some 11 years ago Kelly earned an M.A. in journalism from Columbia University, and since then he has written extensively on the environment.

able accomplishment of the citizensof southern California. Los Angeles is one of the few places in the nation where air quality has improved dramatically since the 1970s. From 1955 to 1992 the peak level of ozoneÑone of the best indicators of air pollutionÑdeclined from 680 parts per billion to 300 parts per billion. The California Air Resources Board recently documented that population exposure to unhealthful ozone levels has beencut in half in just the past decade. Furthermore, the smog levels measured during each of the past three years have been the lowest on record. All these improvements were achieved at a time when human activity in the Los Angeles area was increasing at a rapid rate. Since the 1950s the population has almost tripled, from 4.8 million to 14 million; the number of motor vehicles on the road has morethan quadrupled, from 2.3 million to 10.6 million; and the city has grown into one of the most prosperous regions of the world. Although the residents of southern

AIR POLLUTION SOURCES have increased in size and number in Los Angeles, yet technical innovation and social policy have led to an improvement in air quality during the past two decades. Some typical sources of air pollution include (from left to right) industrial coatings, barbecues, trash incinerators, paints, dry cleaners, commercial ovens and motor vehicles.

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SCIENTIFIC AMERICAN October 1993

Copyright 1993 Scientific American, Inc.

California still face and continue to tackle many air pollution problems, they have an advantage in that they have spent 50 years studying the local atmosphere and experimentingwith various policies. We hope the cities of all nations will learn from the experiences of Los Angeles [see ÒThe Changing Atmosphere,Ó by Thomas E. Graedel and Paul J. Crutzen; SCIENTIFIC AMERICAN, September 1989]. he movement to clean up the air in southern California began during the 1940s, a period of rapid industrialization. At the time, the region was plagued by sudden Ògas attacksÓ thatirritated the eyes, diminished visibility and produced an unpleasant odor. Then, as now, the smog was so obvious and odious to the public that elected leaders were compelled to take meaningful action. Yet their efforts provoked strong conßict. Some citizens and industries Þercely resisted suggestions to clean up sources of pollution. But the Los Angeles Times published dozens of editorials demanding...