(Reuters) - Massive clouds of smoke spewed from U.S. wildfires raging ever more intensely in recent summers send soot, carbon monoxide and other toxins far and wide, posing health hazards for distant communities, scientists warned in a study on Thursday.
The Natural Resources Defense Council report was based on government satellite images of smoke plumes from 2011, the latest such data available, providing a national snapshot of wildfire-related air pollution that year.
Wildfires burning through drought-parched forests and grasslands in 2011, mainly in the western half of the country, belched smoke into 32 states, diminishing air quality for nearly two-thirds of the U.S. population, the report found.
Eight of those states, including Illinois and Ohio, experienced smoky air measured at "medium- to high-density" levels for at least a week despite an absence of any wildfires within their borders, the study said.
A number of Midwestern states endured 12 days or more of smoky air deemed to be in the unhealthy range that year, the report said.
"Even if you don't live near wildfires, your health may be threatened by smoke," Kim Knowlton, NRDC scientist and assistant professor of environmental health sciences at Columbia University, said during a telephone press conference Thursday.
The 2011 wildfire season was particularly destructive, with more than 74,000 blazes collectively charring nearly 9 million acres nationwide, according to the National Interagency Fire Center in Boise, Idaho.
Wildfire smoke contains hundreds of toxins as well as tiny particles that can lodge deep in the lungs and cause damage, said Patrick Kinney, professor at Columbia University's Mailman School of Public Health.
Numerous scientific studies show exposure to heavy smoke levels can worsen respiratory conditions such as asthma and increase the rate of premature death due to heart and lung problems, he said.
The study did not seek to quantify how many people may have suffered health problems from hazardous air quality linked to wildfires in 2011.
With prolonged drought and rising temperatures tied to climate change predicted to intensify wildfires in the coming years, particularly in the western United States, government health officials are scrambling to address the spread of smoky air as an issue of growing concern, Kinney said.
Heightened worries about pollution from wildfires come at the end of a 2013 wildfire season during which the Rim Fire in and around Yosemite National Park - one of the biggest California blazes on record - sent dense smoke south to the San Joaquin Valley and east to Nevada, triggering unhealthy air alerts in those areas.