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Studying the impact of wildfires on air quality, environment

April 07, 2016

AMHERST, Mass. - Research assistant professor Ezra Wood at the University of Massachusetts Amherst has been awarded a four-year, $800,000 grant from the National Oceanic and Atmospheric Administration (NOAA) to participate in one of the largest studies to date of atmospheric chemistry in wildfires. It will focus on North America, but results should apply to many areas around the world where fires occur, such as those used to clear forests for agriculture in Indonesia and Brazil, Wood says.

The work, to be conducted with co-investigators from Aerodyne Research, Inc. of Billerica, Mass., will advance understanding of the effect fires have on the environment and the atmosphere. Field work will begin in October.

"With climate change, forest fires are likely to be more intense and frequent," he points out. "And the use of fire for forest clearing is a very common practice, as is burning biomass as fuel. Overall, we will address what is being emitted, what gases and what sorts of particles, and in what quantities. We'd like to be able to help modelers predict, for example, if you burn this many acres or woodland, how many grams of compound A and particle B will be released into the atmosphere, what happens to them chemically and how long they persist."

Some materials emitted by wildfires are transformed chemically by sunlight, the atmospheric chemist notes. Some of these are very short-lived while others last much longer. Also, the properties of some compounds are altered by processes called chemical aging. Some organic compounds start out as gas, for example, but after undergoing photochemistry from exposure to sunlight they turn into particles, he points out.

Interestingly, Wood says that one of the biggest unknowns in this field is the nighttime atmospheric chemistry of wildfires, and this will be one of the largest studies to investigate such differences.

"Combustion is often different at night," he says, "because there is higher humidity and cooler temperatures. The fire may smolder more and have less open flame. We also know that pollutants emitted from the ground at night usually don't mix as well in the atmosphere as they do during the day; the smoke and other emissions can hang near the surface until the sun comes up and causes vertical mixing in the atmosphere. This is one of the most under-studied areas and I'm looking forward to making some interesting discoveries."

In addition to climate change affecting wildfire incidence, fires also affect climate, Wood says. Particles emitted from fires can have both a warming and a cooling effect. Light-colored particles reflect sunlight and have a cooling effect, while black or dark-colored ones absorb sunlight and have a warming effect. "These optical properties can change as they are processed in the atmosphere. Particles also affect cloud formation, brightness and lifetime, all of which affect climate," he adds.

During the first year of the study, Wood and colleagues will conduct experiments at a fire laboratory in Missoula, Mont., where known quantities of different fuels can be burned in a controlled environment and the pollutant emissions analyzed by many different research groups' analytical instrumentation. This information on emission factors for different fuel types can be used as inputs to models that predict the impact of forest fires on air quality and climate change.

In the later years of this work, the scientists will use research aircraft and a ground-based mobile air-sampling laboratory for analyses near and far from an actual wildfire. In particular, Wood will focus on hydrogen oxide radicals, which are short-lived catalysts that initiate some of the atmospheric chemical reactions in and around blazes.

Quantifying such radicals will help to answer questions about how long the compounds last in the air and to characterize what happens to compounds that are formed in the smoke plume and not emitted directly by the fire, such as ozone. This work will complement Wood's ongoing research on hydrogen oxide radical chemistry in non-burning forests, which is currently supported by the National Science Foundation.

Wood and colleagues' study is part of NOAA's Fire Influence on Regional and Global Environments Experiment (FIREX) project.

University of Massachusetts at Amherst

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