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Fires and soil emissions are elevating air pollution in remote forests

In remote forest areas of California, air pollution is on the rise, and new research indicates that wildfire and soil emissions are the culprits behind the increasing levels of nitrogen dioxide. This revelation was recently published in a paper in the journal Environmental Research Letters.

Nitrogen dioxide, while short-lived in the atmosphere, is crucial in the formation of ozone and particulate matter pollutants, which are known to cause respiratory problems and asthma in humans, as well as damage plants and crop yields. 

Elevated nitrogen dioxide levels 

By analyzing summertime surface and satellite concentrations of nitrogen dioxide from 2009 to 2020, the researchers found that levels decreased by 2-4.5 percent per year in urban areas across California. 

However, in rural areas, the concentrations remained relatively constant, and in remote forests, there was a worrying increase of approximately 4.2 percent per year.

“Forested areas show a steady, rapid rate of increase in summer. The trend is alarming,” study senior author Professor Ian Faloona of UC Davis

Studying remote forests

To conduct the study, scientists used surface nitrogen dioxide levels collected by the state and NASA’s Aura satellite. They then categorized areas of nitrogen dioxide in the atmosphere by surface temperature and soil moisture levels. 

The team also utilized a California database of fire incidents to classify lands into one of five categories: urban, forests, croplands, scrublands, and barren (little vegetation).

What the researchers learned 

While controls on internal combustion engines and other fossil fuel emitters have successfully reduced nitrogen dioxide levels in urban areas, continuous satellite data revealed that this positive effect is not replicated in rural and remote forest areas. 

In these regions, wildfires and emissions from soils, especially agricultural soils with fertilizer use, are correlated with an increase in nitrogen dioxide levels. 

“Soils, and wildfires in particular, are really going to become steerers of the ship of our air pollution. We have to put a lot of effort into curtailing the effects of wildfires and understanding better our emissions from agricultural soils,” said Professor Faloona.

What the future holds for remote forests

The study suggests that areas with high fertilizer use can be sources of nitrogen dioxide emissions as microbes compete with crops for nitrogen. This process generates gaseous nitrogen compounds. 

“Our results point to opportunities for different sets of policies and technologies to assist in reducing nitrogen dioxide concentrations in rural and economically disadvantaged areas of California, but will require a concerted effort to better understand the exact environmental dependence of soil and wildfire emissions,” wrote the study authors. 

This research highlights the importance of addressing non-traditional sources of pollution, such as wildfires and agricultural soils, as regulators seek to further decrease pollutants. 

As fossil fuel emissions continue to decrease due to current emission management actions, it is imperative to address and understand other historically overshadowed sources to ensure comprehensive air quality policy in the future.

The research was funded by the U.S. Department of Agriculture’s National Institute of Food and Agriculture.

More about soil emissions

When discussions about climate change arise, topics such as deforestation, burning of fossil fuels, and industrial emissions often dominate the conversation. However, a critical yet lesser-discussed component of the carbon cycle lies right beneath our feet: soil emissions.

What are soil emissions?

Soil emissions refer to the release of gases from the soil into the atmosphere. These gases primarily include carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). All of these are greenhouse gases (GHGs) that contribute to the greenhouse effect and subsequent global warming.

The science behind soil emissions

Soils are teeming with life. They are home to a plethora of microorganisms, plants, and animals. When these organisms respire, decompose, or excrete waste, they release carbon in the form of CO2. This natural process is vital for nutrient cycling and soil health.

However, in anaerobic or oxygen-deprived environments like wetlands or waterlogged agricultural fields, methane, a GHG much more potent than CO2, is produced. Another significant gas, nitrous oxide, is emitted from soils due to microbial processes that transform nitrogen available in the soil.

Human activities amplifying emissions

Human interventions have exacerbated the rate of these soil emissions. Here are some examples.

Agricultural Practices: The excessive use of nitrogen-based fertilizers in agriculture can increase nitrous oxide emissions. Similarly, flooded fields, as seen in rice paddies, can become hotspots for methane emissions.

Deforestation: Trees and plants capture and store carbon. When they are removed, not only is this carbon storage capacity lost, but the disturbed soil also emits the stored carbon back into the atmosphere.

Drainage of Wetlands: Wetlands naturally emit methane. However, when they are drained for agriculture or development, the exposed organic matter rapidly decomposes, releasing large amounts of CO2.

The climate implications

While soil emissions are natural, the amplified release due to human activities is a concern. Collectively, soils release more CO2 than all human activities combined, making them a significant carbon sink. Any alteration to this balance could have cascading effects on global climate patterns.

Methane, despite being emitted in smaller quantities than CO2, is over 25 times more effective at trapping heat in the atmosphere. Nitrous oxide, on the other hand, is 300 times more potent as a GHG than CO2 and also plays a role in the depletion of the ozone layer.

Towards sustainable soil management

Addressing the challenge of increased soil emissions requires a multi-faceted approach.

Regenerative Agriculture: This includes practices like crop rotation, cover cropping, and reduced tillage, which improve soil health and reduce the need for synthetic fertilizers.

Afforestation: Planting trees and restoring natural habitats can capture atmospheric CO2 and enhance soil carbon storage.

Wetland Preservation: Protecting wetlands can prevent the large-scale release of GHGs while preserving biodiversity.

In summary, while soil emissions are a natural part of the Earth’s carbon cycle, human interventions have disturbed this delicate balance. As efforts to combat climate change intensify, understanding and mitigating enhanced soil emissions will be crucial.

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