A recent study from the University of California, Davis reveals a startling statistic: around 25% of nitrogen oxide (NOx) emissions in California’s Salton Sea air basin stem from soil rather than traditional sources.
Researchers calculated the average daily soil emissions to be approximately 11 tons, a figure dramatically higher than the state’s current estimate, which suggests soil NOx emissions are ten times less.
Urgent Need for Research
Published in Scientific Reports, this research highlights an urgent need to deepen our understanding of emissions from agricultural soils.
Such insights are vital for meeting state and federal air quality standards and for improving the air quality in rural regions like the Imperial and Coachella Valleys, areas prone to high temperatures and extensive agricultural activity.
While cities like Los Angeles have witnessed considerable improvements in air quality thanks to reduced emissions from industry and transportation, rural areas are seeing a troubling rise in NOx emissions.
This increase is linked to various factors, including wildfires and the emissions output from agricultural soils.
Impact on Communities
Ian Faloona, a professor at UC Davis and the study’s lead author, suggests that the impact of wildfires and emissions from soil will likely gain importance as the century progresses.
According to him, regulatory measures must evolve in response to this trend, especially considering its effects on rural and suburban populations.
He pointed out that improvements in air quality have plateaued in many California regions over the past eight years, largely due to the overlooked roles of soil and wildfire emissions.
The Salton Sea region is known for having some of the most polluted air in the United States.
Spanning from Palm Springs through Coachella Valley and into the Imperial Valley, it stretches down to the Mexico border at Calexico.
This area plays a crucial role in California’s agricultural sector, which generates over $2 billion annually through diverse crop production, yet the predominantly Latino population faces significant hardships, including high rates of poverty and respiratory illnesses like asthma.
Understanding Emissions Dynamics
NOx emissions are particularly concerning as they lead to ozone and particulate matter formation in the atmosphere.
Factors such as excessive fertilizer use, irrigation, and rising temperatures are known contributors to increased soil NOx emissions—conditions that are prevalent in this hot, agricultural region.
California currently experiences some of the nation’s fastest temperature increases during warm seasons, exacerbating risks from wildfires and enhancing microbial activity within the soil.
Notably, fertilizer sales for sandy soils in Imperial County have skyrocketed by 137% since 1991.
To delve into these dynamics, researchers conducted on-site sampling between June 2022 and April 2023 at an Imperial Valley high school and an air monitoring station located on Torres Martinez Desert Cahuilla Indian land in Coachella Valley, collaborating with Comité Cívico del Valle, a local community organization.
The team analyzed these samples at the UC Davis Stable Isotope Facility.
They utilized isotopic signatures and a Bayesian Mixing Model to gauge how much soil contributes to the overall emissions profile.
Their findings indicate that soil emissions have been significantly underestimated, with factors like nutrient availability, soil moisture, and temperature playing pivotal roles.
The study authors recommend that gathering more information regarding fertilizer applications and irrigation practices could significantly enhance understanding of how these activities directly affect emissions.
Such knowledge would aid regulatory authorities in strengthening air quality initiatives in the area.
Faloona expressed alarm that soil emissions and wildfire smoke are frequently viewed as background pollutants.
He argued that these emissions are on the rise and are becoming major contributors to pollution across many parts of California.
Current assessments, he maintained, are not adequately reflecting the seriousness of these pollution sources.
Heather Lieb led this research, completing her Ph.D. under Faloona’s mentorship at UC Davis.
Financial support came from the UC Davis Environmental Health Sciences Center, the National Institutes of Health, the Western Center of Agricultural Health and Safety, and the USDA National Institute of Food and Agriculture.
Source: ScienceDaily