By Joseph Serna, Los Angeles Times (TNS)

LOS ANGELES — Despite increasingly aggressive clean air and fuel standards, years of drought are taking a toll on California’s air quality, the American Lung Association says in a new report.

The portion of California’s Central Valley from Fresno to Madera was the most polluted region in the nation on any given day in 2013 with microscopic particulates, or soot, thanks in large part to the changing climate and drought, according to an annual report on air quality released Wednesday by the American Lung Association.

“Continuing drought and heat may have increased dust, grass fires, and wildfires” that have hurt the Central Valley’s air quality in short-term particle pollution, the report stated. “The impact of climate change is particularly apparent in the West, where the heat and drought create situations ripe for episodes of high-particle days.”

The report evaluated metropolitan areas based on recorded levels of ozone, the main ingredient in smog, and also measured particles, or soot, that tend to build up in colder, winter months. It looked at the annual average for cities and the worst on average in a 24-hour period. The report used data gathered between 2011 and 2013.

In both time frames, a swath of California’s Central Valley topped the rankings for unhealthy particulate pollution. The Fresno-to-Madera region was the most polluted year-round for the second year in a row and the worst in a 24-hour cycle.

Bakersfield was ranked second, the area from Visalia to Hanford was third and the area from Modesto to Merced was fourth for short-term and annual particle pollution.

Los Angeles County actually performed worse in the 24-hour rankings this year than it did the previous year, the report noted.

Despite great strides in recent years, L.A. County again topped the nation’s list of metropolitan areas with the worst smog for 2013, according to the report.

L.A. County has ranked the worst for smog among metropolitan areas in all but one of the association’s 16 reports. Despite the high rank, the report said the city “exemplified” progress in reducing smog.

Its three-year average for 2011-13 was its best since the report began and showed a one-third reduction in the number of unhealthy air days.

Ranking fifth on the list of smog-polluted areas nationally, according to the report, was the area from Sacramento to Roseville.

Smog forms in warm, sunny weather with little wind. More than 138 million people, or 44 percent of the nation, live in areas with unhealthy air, according to the report.

Still, the situation has improved over the last ten years.

“Even the more polluted cities had significantly fewer unhealthy ozone days than they had a decade ago,” the report states.

Poor air quality can most adversely affect the young and old, those with lung disease and asthma, heart disease and diabetes.

The report said that the Environmental Protection Agency’s current ozone air quality standards are “woefully inadequate” and called for the government to adopt stricter standards proposed by the EPA last year.

Photo: Ben Amstutz via Flickr