Wildfire smoke

Nearly a third of the U.S. population lived in counties affected by wildfire smoke in 2011, according to an analysis of satellite data by the Natural Resources Defense Council. (Natural Resources Defense Council / October 24, 2013)

Wildfire smoke poses a growing health risk to millions of Americans, even for those who live hundreds of miles from the flames, a new report by an environmental group says.

About two-thirds of Americans, or nearly 212 million people, lived in counties that two years ago contended with wildfire smoke linked to respiratory problems like asthma, pneumonia and chronic lung diseases, according to a report released Thursday by the Natural Resources Defense Council.

The group used satellite imagery of smoke plumes from the 2011 wildfire season - one of the worst in recent years - to take a nationwide snapshot of air quality. The analysis found that the extent of the country affected by wildfire smoke was 50 times greater than the area burned in the fires.

It’s no surprise that many of the smokiest states had major blazes that year. That includes Texas, which topped the list with more than 25 million people living in places with air fouled by wildfires for a week or more, followed by Florida and Georgia.

But six of the worst states, including Illinois, Missouri, Iowa and Kansas, experienced more than a week of medium- to high-density smoke even though they had no major fires, the report found. That’s because smoke drifts far downwind of fire perimeters, spreading health effects across state lines.

"Fires are not only a local issue but a national one because smoke can pose serious health risks to people far away," said Kim Knowlton, an NRDC senior scientist who led the analysis.

The problem is poised to worsen with climate change as warmer temperatures, longer dry seasons, decreased snowpack and drought increase fire risk, the report says. Other factors increasing the risk of fire and smoke include more people moving into fire-prone areas and a history of wildfire suppression that is making blazes more intense.

Some of the most harmful components of wildfire smoke are fine particles, which can lodge deep in the lungs and lead to a host of respiratory and cardiovascular problems. Particularly vulnerable are children, the elderly, pregnant women and people with preexisting conditions like heart disease.

In one study cited in the report, UC Irvine researchers found that Southern California’s 2003 wildfire season resulted in 69 premature deaths, 778 hospitalizations, 1,431 emergency room visits and 47,605 outpatient visits.

The NRDC report found significant smoke levels in some regions, including the Great Plains, that have few devices monitoring the air for fine particles.

“We need to have more monitoring and prevent all the conditions that are making fires and smoke worse,” Knowlton said.

tony.barboza@latimes.com

Twitter: @tonybarboza