Agriculture is a Major Source of Nitrogen Oxide Pollution in California

Caroline Petrow-Cohen

California supports 12.2% of the national food economy and is the world’s 6th largest economy based on gross national product. Nitrogen Oxide (NOx = NO + NO2) has been recognized as a problem as several of the United States’ worst air quality districts are in the rural regions of California. Policies have been made to limit NOx pollution from fossil fuel sources, but NOx emissions from agricultural soils have been largely overlooked. Agriculture is a large source of NOx in the US, especially where fertilizer use is substantial. It is estimated that Californian agricultural NOx emissions may make up 20% to 51% of the state’s total NOx emissions. As this is a large amount of the state’s air pollution being surpassed, an assessment of agriculture’s impact on NOx is needed and performed in the following study.

The Study

This study looks to examine the amount of NOx emissions from agricultural areas in California and compare them to global data. The study hypothesizes that the emissions from agricultural areas will be much higher than previously believed.


The results confirmed the hypothesis of NOx emissions from agricultural soil in California being the dominant source of NOx emissions, thus meaning there is a large, unrecognized source of pollution within the state. Fertilization increases the emissions as fertilized cropland composed 20% to 32% of total NOx emissions while natural soil composed only 5% to 9%. Especially high emissions are found in the Imperial Valley region, in the Southern part of the state, which is most likely as a result of high temperatures, dry soils, and high fertilizer inputs, all of which are known to affect NOx emissions. Increases in fertilizer and population grown likely accelerate NOx soil emissions as well.

What’s So Bad About NOx Pollution?

NOx pollution is one of the most important and detrimental aspects of air pollution. Air pollution is responsible for one in eight premature deaths worldwide, as well in declines in biodiversity and worsening climate change. Air pollution also can cause upper respiratory disease, asthma, cancer, birth defects, cardiovascular disease, and sudden infant death syndrome. Not only is air pollution dangerous, but fertilizer is costly, and costs the US $210 billion dollars per year in health related and environmental damage.

Why Is This Relevant?

As food demand increases, fertilizer use is expected to increase to keep up with demand, and subsequently NOx emissions are expected to increase. Increased NOx emissions and air pollution could also result from the heat waves and droughts as a result of recent climate changes in California. Seeing as agricultural soils are a substantial source of NOx emissions, a better understanding of agriculture’s effects on air pollution is necessary. Reducing NOx emissions would improve both the economy and environmental health.

What Can We Do About It?

Several techniques which already exist could be used to reduce the amount of NOx emissions as a result of fertilized croplands. Precision fertilization can decrease the amount of emissions. Cover crops that consume leftover fertilizer can be incorporated into cropland soil, which would reduce the amount of fertilizer application necessary. Livestock manure and the fertilizer used to grow livestock feed are big sources of pollution in both air and water, thus it would be beneficial to promote plant consumption instead of livestock. Additionally, it would help to promote the change to a gas such as dinitrogen (N2), instead of NOx, which has less impacts on the environment. Finally, improved and alternative irrigation strategies would also reduce harmful N losses in agriculture.

Praesana Danner ‘19



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