A new study suggests that polluted areas where wildfires burn may cause emissions that are even more toxic than in areas that have good air quality.
Nitrogen is released into the atmosphere when people burn fuels in cars, power plants, factories and in other ways. It is then absorbed by plants, which use the gas in order to grow. However, too much nitrogen in the atmosphere can actually result in "nitrogen saturation." This can ultimately lead to a decrease in biodiversity, changes in plant species and contamination of nearby soil and water.
Researchers from the University of California, Riverside and the U.S. Forest Service's Pacific Southwest Research station decided to see whether nitrogen saturation would actually cause a difference in forest fires. They looked at a 60-mile stretch of forest land to the east of the Los Angeles metropolitan area. The pollution concentrations in the area actually decreased from west to east, which meant that the region was perfect for studying the effects of pollution.
The research team selected sites 55 miles apart and collected deposited material from the forest floor. This litter is the primary fuel source for forest fires.
It turns out that litter from the polluted site had a higher nitrogen content than litter from the cleaner site. More interesting, though, was what the researchers found after burning the samples of litter.
They discovered that the litter from the polluted site released more nitrogen oxides than the litter from the clean site. Nitrogen oxides help contribute to the formation of smog and ozone, which means that polluted areas are likely to become even more polluted if they're hit by forest fires.
That's not all that the polluted materials released. It turns out that the litter also release more small fine particles, which can contribute to respiratory health problems in people.
"The environmental impact of prescribed burns has historically been based on data from clean fuels in areas of good air quality, so we have likely been under-predicting the impact of biomass emissions in polluted areas," said Akua Asa-Awuku, a researcher at UC Riverside's Bourns College of Engineering and lead author of the study. "This study, and specifically the concern that biomass grown and burned in polluted areas is potentially more toxic to human health, is additional evidence that human activities have consequences not yet explored and therefore not understood."
The findings tell researchers a bit more about how wildfires may impact areas that have been polluted by nearby cities, as well as other sources of pollution.
The study was published in the March 1 issue of the journal Environmental Research Letters.
