A 20-year study of Los Angeles-area children found decreasing air pollution led to fewer respiratory and bronchitis-like symptoms.

Beginning in 1993, the University of Southern California's Children's Health Study tracked over 4,600 kids in eight communities, including Long Beach, Riverside and Lake Elsinore. Pollution reduced across the southland in that span, allowing asthmatic and non-asthmatic children alike to freely breathe in cities notorious for their unsafe emission levels.

"Several studies indicate that exposure to elevated concentrations of ambient air pollution, often levels below regulator standards, is associate with large increases in the bronchitic symptoms among children with asthma, potentially resulting in a heavy burden of disease in exposed children with substantial economic costs," read the study, published April 12 in the Journal of the American Medical Association.

Researchers began by splitting the kids into three groups, differentiating between those with and without asthma. They were separated by gender, ethnicity, age and living conditions. Cockroach infestations, pet ownership, and secondhand smoke in the home were also taken into account.

The biggest benefactors were kids with asthma, who saw a 32 percent drop in breathing problems. Those without asthma were 21 percent less likely.

Nitrogen dioxide and ozone pollutant levels dropped across each community, with the exception of Long Beach and Santa Maria. Tiny particles called particulate matter -- harmful particles that delve deep into ones lungs -- fell by 47 percent in a 19 year span, dating back to 1992.

Latino Children Report Fewer Breathing Problems

In terms of race, the study was divided into Hispanic -- which accounted for about 45 percent of the children -- and non-Hispanic white groups.

The proportion of Latino children increased from 29.4 percent between 1993-2001 to 55.7 percent from 2003-2012, the latter marking a period when a high portion of parents completed Spanish-language questionnaires.

Regardless of pet cats or dogs, tobacco use in the house, or pre-existing asthma problems, Latino children as a whole saw respiratory improvement over the last two decades.

"The shift in ethnic composition across the 3 cohorts with a growing Hispanic population and lower socioeconomic status is a potential source of bias," researchers wrote. "However, bias in the estimates from this change in ethnic distribution is not likely to have a major effect because sensitivity analyses based on models that only considered Hispanic children gave results that were similar to those that included all children."

Last August, political opinion research firm Latino Decision released a survey indicating 85 percent of registered Latino voters believe smog and air pollution reduction is either "extremely" or "very" important; 78 percent thought developing clean energy sources was just as important.

Children Across the State Affected

The American Lung Association's 2015 "State of the Air" report lists California cities as the five worst ozone pollution offenders, in addition to holding the country's seven worst cities for year-round particle pollution.

Los Angeles-Long Beach rank first and fifth in each category, respectively, but Northern California towns take the remaining top slots. Fresno-Madera rank number one in both short and long-term particle pollution, thanks in large part to vast farmlands left baron by the state's ongoing drought. Dust particles from dust, soil, and wildfires sift in the air, leaving children susceptible to respiratory problems.

Air quality districts aim to curve pollution levels in rural areas by updating standards for wood stove heaters. Curving vehicle pollution in Bay Area cities is a whole other issue.

Children in Oakland are just as likely to inherit lung problems as Los Angelinos. They develop coughing, congestion, and bronchitis-like symptoms in the same jam-packed freeways and visit hospitals just as often.

About one in 10 children in the United States have asthma, according to a 2009 Centers for Disease Control and Prevention study. Medical costs in 2007 exceeded $56 billion, costing U.S. taxpayers about $3,300 per person each year.