How Air Pollution Makes Wildland Fires Worse

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In recent years, we’ve seen wildfires reach taller, burn fiercer, and stretch wider than ever before. While global warming is a significant factor increasing the severity and frequency of wildfires, recent findings show air pollution also plays a role.

A recent study conducted by the United States Forest Service and the University of California, Riverside showed that wildfires in areas with higher air pollution released more nitrogen oxides — pollutants that negatively affect the environment and people’s health. Today we’re going to take a closer look at this study and discuss the meanings of its findings.

Understanding Nitrogen Saturation

Before we jump in, let’s take a step back to understand one important aspect of air pollution: the release of nitrogen. This gas is released into the atmosphere when fuels are burned from our cars, factories, and other sources. While a reasonable amount of nitrogen is absorbed by plants, an overload of nitrogen leads to “nitrogen saturation” — in essence, we’re producing more nitrogen than the plants can absorb, and it’s negatively affecting the environment. Decreases in biodiversity and water contamination are just a couple outcomes of nitrogen saturation.

Studying Nitrogen Saturation and Wildfires

Researchers from The United States Forest Service and the University of California, Riverside wondered if there was another, unexplored, outcome of nitrogen saturation — one that affects regions burned by fire. They conducted a study aimed at understanding how nitrogen saturation affects the atmosphere during wildfires. When a fire burns biomass material, like plant and tree matter, it releases a combination of gases and aerosols into the atmosphere. The study questioned whether the existence of nitrogen saturation in the atmosphere had any impact on those gases and aerosols released during a wildfire.

Researchers, led by Akua Asa-Awuku of the University of California, Riverside, compared emissions at two points 55 miles apart in the San Bernardino Mountains (outside of Los Angeles). This was done by collecting samples from the forest floors of each site, and burning them in controlled lab experiments — in this way, the researchers were able to observe how the earthy soil and biomass material in those areas reacted under fire. The western location, being closer to Los Angeles, had more exposure to air pollution than the eastern location. Apart from this, both points experienced similar weather conditions.

The Study’s Findings

Results showed that samples collected from the western point (higher air pollution) released more nitrogen oxides than those from the eastern point. Western point samples also released greater quantities of small fine particles, which are linked to respiratory problems. In other words, wildfires have negative effects on air quality apart from smoke.

These findings are in conjunction with another study, conducted in the Santa Monica Mountains, that showed an increase in nitrogen oxides negatively impacting native plants in the area. Invasive grasses from the Mediterranean grow at a better rate in the presence of nitrogen oxides than native plants. This means areas with higher levels of nitrogen oxides (such as near populous cities) have more non-native grass pushing out the plants that grow there naturally. In the event of a forest fire, these invasive species produce fuel that results in larger fires, further destroying native species.

Implications for Wildfire Management

How can we use these findings for controlling wildfires? One common method for wildfire management is called controlled burning, also known as prescribed fire. Benefits of controlled burning include protecting communities, recycling nutrients back into the soil, and improving habitats for endangered wildlife. Asa-Awuku recommends agencies look at the study’s findings when determining the impact of controlled burning. According to her, controlled burns are traditionally studied using samples from clean fuel and in areas with good air quality. She believes these studies may have been underestimating the fuel’s impact in areas of poorer air quality.

Implications Beyond Wildfires

Areas with higher population density — which traditionally see higher levels of air pollution — can be further impacted by increased emissions from wildfires. Wildfire seasons have been officially expanded in areas including Alaska, and are understood to last longer than usual in the West and Pacific Northwest. Even if regions don’t have the same population densities as Los Angeles, factories, power plants and other fuel-burning equipment can have the same effects.

Asa-Awuku explained that this study adds to a growing list of negative consequences from burning fossil fuels. In fact, the results imply there are likely additional consequences to burning fossil fuels we haven’t even discovered yet. The impact of wildfires go beyond property damage and a scorched environment, and must be taken into consideration as we develop strategies to defend against them.

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