Farming: a Major Contributor to Air Pollution in California

Nitrogen oxides (NOx = NO + NO2) are a primary component of air pollution. These nitrogen gases react in the atmosphere to form tiny particulate matter that have been linked to upper respiratory disease, asthma, cancer, birth defects, cardiovascular disease, and sudden infant death syndrome . Nitrogen oxides are a major precursor to the formation of particulates.

Particulate matter has immediate health impacts: itchy, watery eyes, increased respiratory symptoms such as irritation of the airways, coughing or difficulty breathing and aggravated asthma. Health effects can result from both short-term and long-term exposure to particulate pollution. Exposure to particles can also trigger heart attacks and cause premature death in people with pre-existing cardiac or respiratory disease.

As NOx emissions from fossil fuel combustion have been reduced in the past decades recent studies have found that nitrogen oxide air pollution from and soil are a major contributor to air pollution. Studies in the United States Midwest have found that 30% of the nitrogen oxide emission is from agriculture. California is considered the world’s sixth largest economy in terms of gross national product and grows about two-thirds of the fruit and nuts and one third of the vegetables grown in the United States. Nonetheless, in the current California Air Resource Board (CARB) NOx inventory, emissions from cars and trucks are officially thought to be responsible for 83% of NOx emissions and soil emissions from agriculture are currently considered negligible.

Though the CARB has instituted policies to reduce NOx pollution from fossil fuel sources, they have not regulated NOx emissions from agriculture and observed levels of NOx around the state were often higher than could be explained particularly in the agriculture-heavy Central Valley of California with many locations remaining “non-attainment” areas for federal particulate air pollution standards. Although some NOx occurs naturally in soils, the majority of NOx gases released from agricultural land are due to nitrogen-based fertilizers applied to crops. About half of the fertilizers end up lost the atmosphere due to poor application techniques.

In a new study published in Science Advances titled “Agriculture is a major source of NOx pollution in California,” Maya Almaraz et al find that agricultural soils contribute a substantial amount of NOx to the atmosphere in California. The scientists used modeling techniques to estimate the NOx emission from California soils. Dr. Almaraz and her colleagues used the amount of fertilizers applied to the soil, soil texture, moisture, temperature, precipitation and crop harvest as factors in the model. They also collected air samples in the agricultural Central Valley of California refine and verify the model. They determined that agricultural land is responsible for between 20% and 32% of NOx air pollution in California. This is a major revision of the previous estimates and increases the estimated NOx released in the state significantly. This places fertilized agricultural lands second behind motor vehicles as sources of NOx pollution.

The scientists expect to see a significant increase as nitrogen based fertilizer use increases to keep pace with food demands in a changing climate. These findings suggest the need to reconsider the role of soil NOx sources and develop implement “best management farming practices” targeted at reducing nitrogen based fertilizer waste and air release.