Long-running study published in New England Journal of Medicine shows that exposure to particulates has decreased dramatically in the past 20 years

This article is more than 5 years old

This article is more than 5 years old

Travel deep into the Los Angeles basin on a hot, stifling, windless day, and you would be hard-pressed to see the stark desert mountains rising directly to the north, distinguish one low-rise suburban community from another, or indeed see much of anything beyond grey asphalt, grey concrete and opaque, relentlessly grey skies.

Smog and Los Angeles are as closely bound in the popular imagination as baguettes and Paris, or sleepless nights and New York. And yet, as locals know but the rest of the world rarely stops to notice, the air quality in America’s second-largest metropolis has been improving dramatically over the past 20 years.

The latest evidence comes in a long-running study of lung development in children, published in Wednesday’s New England Journal of Medicine, which shows that exposure to both nitrogen dioxide and small particulates has dropped dramatically since the late 1990s.

Children living in five notoriously smoggy parts of greater Los Angeles showed improved lung growth of about 10% between the ages of 11 and 15, compared with children at the same age 20 years ago.

“Reduced lung function in adulthood has been strongly associated with increased risks of respiratory disease, cardiovascular disease and premature death,” the lead author of the study, James Gauderman of the Keck School of Medicine at the University of Southern California, said in announcing the results.

Facebook Twitter Pinterest The San Bernardino mountains are visible in the distance behind the downtown skyline. Photograph: Zuma/Rex

“Improved air quality over the past 20 years has helped reduce the gap in lung health for kids inside, versus outside, the LA basin.”

The city’s bragging rights are limited, because it is still the most polluted city in North America – despite some stiff competition from Houston, the Washington DC area, and Pittsburgh.

Still, anyone who lives there knows just by riding the freeways that the mountains are clearer, the downtown skyline is more visible and the beach heaves into view much more readily than it did when Seinfeld was the biggest hit on television and southern California’s most notorious presidential intern, Monica Lewinsky, was all over the 24-hour news cycle.

According to the latest analysis by the American Lung Association, Los Angeles had 68 fewer high-ozone days last year than in 1996, and 75 fewer high-particulate-matter days than in 2000.

The reasons are no mystery: ever since the introduction of the catalytic converter in 1975, California has led the country in both regulating vehicle emissions and in shepherding technological advances to make those reductions more attainable.

Because of Los Angeles’s chronic smog problem, Congress gave California the right to set its own, more stringent anti-pollution measures back in 1967.

While the local population has continued to skyrocket, new suburbs keep sprouting and cars on the roads multiply as if they were breeding – the number has roughly doubled since the 1990s – pollution levels have been heading in the opposite direction.

Hybrids and electric cars, improved public transport systems and better engine technology have all contributed.

According to the USC study, those changes have led to fewer stunted lungs and fewer children susceptible to asthma and a host of other respiratory disorders.

Facebook Twitter Pinterest Not long ago, a typical day in Los Angeles looked a lot like this. Photograph: David McNew/Getty Images

The study followed children in communities including Long Beach – home to the largest port in the United States, where huge trucks rumble through day and night to meet the arriving container ships bringing consumer goods from Asia – and Riverside, a baking suburban city in the so-called Inland Empire, 80 miles from the beach and hemmed in by the San Bernardino mountains to the north and the San Gorgonio Pass, gateway to the high desert, to the east.

Overall, the percentage of children with abnormally low lung function at age 15 dropped from nearly 8% in 1994-98, to 6.3% in 1997-2001, to just 3.6% in 2007-11.

Whether Los Angeles can keep the improvements coming, however, is open to question.

Geography is the abiding problem: the mountains tend to trap air, and rainfall to wash the pollutants away is rare enough at the best of times.

The drought that has beset California for the past four years and could, according to some studies, become a more permanent feature because of global warming is a major preoccupation.

“We can’t get complacent,” Gauderman said, “because not surprisingly the number of vehicles on our roads is continually increasing. Also, the activities at the ports of LA and Long Beach, which are our biggest polluting sources, are projected to increase.”