They concluded that for every decrease of 10 micrograms per cubic meter of particulate pollution in a city, average life span increased a little more than seven months -- about the same amount seen in previous, smaller studies.
"We are getting a return on our investment to improve air quality," Pope said.
Overall, the average life span in the 51 areas increased 2.7 years over the two decades, with the major share of the increase attributed to reductions in smoking and changes in socioeconomic factors.
Los Angeles, and Southern California in general, had large increases in life expectancy during the period, even though pollution levels did not drop as much as in other cities. Pope attributed the increase in life span to a string of smoking bans begun in 1994.
Pope thinks there is room for further improvement. The average countrywide fine-particulate concentration in the early 1980s was about 20 micrograms per cubic meter, and that dropped to about 14 micrograms by 2000.
"It's reasonable to expect that we could reduce it by that much again, but then we reach a point of substantially diminishing marginal returns," he said.
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thomas.maugh@latimes.com
