Do you ever wonder what gives smog its grotesque brown hue?

The answer: nitrogen oxides.

Nitrogen oxides, collectively called NOx, are a family of poisonous, highly reactive gases. Three of the most notorious nitrogen oxides are:1

• nitric oxide (NO)
• nitrogen dioxide (NO₂)
• nitrous oxide (N₂0)

NOx is a powerful oxidizing agent. It plays a significant role in the atmospheric reactions with volatile organic compounds (VOCs) that produce smog on hot summer days.²

NOx is also a major part of acid rain and contributes considerably to global climate change.

Health effects of NOx pollution

NOx pollution isn’t just offensive to look at — it’s also toxic to breathe. Short-term exposure to nitrogen oxides can cause a variety of serious health effects, including:³

• irritation of the respiratory system, eyes, and skin
• aggravation of respiratory diseases, especially asthma
• coughing and choking
• nausea
• headache
• abdominal pain
• difficulty breathing

Long-term exposure to low levels of NOx can cause asthma and respiratory infections. The health effects from very high concentrations of nitrogen oxides can include:

• death
• genetic mutations
• harm to a developing fetus
• decreased female fertility
• spasms
• swelling of the throat

Significant sources of NOx pollution

Volcanoes, oceans, and lightning strikes naturally produce nitrogen oxides. But the prominent presence of this noxious pollutant is largely attributed to man-made sources like vehicle exhaust gases and emissions from electrical power plants.⁴

Most governments concentrate most of their NOx-reducing initiatives on regulating vehicle and industrial emissions because these are traditionally the most significant sources of NOx pollution.

But there’s been a flurry of recent research that reveals another huge source of NOx emissions that’s been underreported — agriculture.

Agriculture’s role in NOx

Big Agriculture (a term for the corporatization of agriculture) regularly gets blowback for employing farming practices that undermine the environment, but its excessive use of fertilizer plays the biggest role in increasing NOx pollution.

How does excessive fertilizer use add to NOx pollution?

Farmers add fertilizer to their crops (basically a load of nitrates) because plants use nitrogen to produce chlorophyll, which is essential for growth. Microbes in the soil feed on nitrate-rich organic matter in the soil not consumed by plants. These microbes produce NOx during their feeding frenzy that contaminates the air.⁵

This may not seem like a big deal since microbes are microscopic – how much NOx could these tiny soil dwellers possibly produce? Well, multiply the thousands of microbes in the soil by millions of acres of farmland, and the amount of NOx released into the air reaches astounding levels.

California’s Central Valley: A breeding ground for NOx

Nowhere else is this link between NOx pollution and widespread fertilizer application more clear than in California, home to one of the most prosperous agricultural regions in the world.

Researchers from the University of California, Davis found that California could have 20% to 51% more NOx pollution than previously thought, thanks to its farmland. That would mean that NOx pollution from farming could result in up to 40% of the total NOx pollution in the Golden State.⁶

This represents a dramatic departure from the California Air Resources Board’s (CARB) estimate that only 3.8% of the state’s total NOx pollution derives from farmland soil.⁷

To obtain these figures, the UC Davis research team, funded by the National Science Foundation, took soil samples and flew over cropland on a plane equipped with a gas-sampling tool to take measurements of NOx emissions.

The study found that six of the worst air quality districts in the US were found in the area of California covered by the study.⁸

The smog that has such a stranglehold in these areas may help explain why children in the Central Valley suffer the highest rates of asthma in California — and the San Joaquin Valley region within the Central Valley, where one in six children have asthma, has the highest rate in the entire country.⁹

The Central Valley is home to a significant number of underserved communities, which are more acutely impacted by air pollution due to greater levels of exposure than are other communities. Additionally, these communities are also more vulnerable to the health effects of air pollution exposure than other groups at the same levels of exposure.¹⁰

Excessive fertilizer use is a global air quality issue

Irresponsible large-scale fertilizer use doesn’t just affect the air quality in California — approximately 30-40% of all NOx pollution worldwide is a result of excess fertilizer in farm fields.¹¹

A study conducted by researchers from the University of California, Berkeley used nitrogen isotope data to find the unmistakable fingerprint of fertilizer use in archived air samples from Antarctica and Tasmania.

The air samples showed a long-term trend in isotopic composition that confirms that nitrogen-based fertilizer is mainly responsible for a 20% increase in atmospheric NOx since the Industrial Revolution.¹²

This dramatic rise in global NOx levels proves particularly worrisome for two primary reasons:

1. After carbon dioxide (CO) and methane, nitrous oxide (NO₂) is the most potent greenhouse gas, trapping heat and contributing to global warming.
2. NOx destroys stratospheric ozone, which protects our planet from harmful ultraviolet rays.

All this to say, fertilizer shouldn’t be vilified — many parts of the world need more of it. The distribution and timing of fertilization on a large scale are what truly need to be overhauled.

How the Asthma Impact Model helps Natalie Sua manage her sons’ asthma

Undaunted by the dire statistics around regional NOx pollution in California, the Central California Asthma Collaborative and Clinica Sierra Vista launched a program to help low-income families in the Central Valley take control over their health and well-being.

Launched in 2013, the group’s Asthma Impact Model focuses on helping low-income families better manage their children’s asthma, thus avoiding visits to the ER.

Witnessing one of her sons struggle to breathe was a disturbingly routine occurrence for Natalie Sua, Fresno mother of six. Three of her six children, all boys, have been diagnosed with asthma.¹³

In the past, when one of her sons suffered a severe asthma attack, Natalie would rush him to the emergency room. But, now, thanks to Fresno’s Asthma Impact Model, Sua has learned how to reduce asthma triggers in her home and effectively manage her son’s asthma through environmental control.

A care coordinator with the program paid visits to Natalie’s home and suggested ways to reduce indoor environmental asthma triggers, like pet dander, dust, and mold. Natalie also was given tips on using natural cleaning products and how to remove mold.

Since working with the Asthma Impact Model, Natalie has noticed a huge difference in the health of her sons — one has even been able to play flag football for the entire season.

Using fertilizer responsibly

Since NOx is produced mostly from excess available nitrogen in soils, one way to reduce NOx emissions is to apply fertilizer sensibly — adding just enough at the right place and time to meet crop demands but avoiding excess amount left over. This measure not only decreases fertilizer costs to producers but also reduces the amount of nitrogen that’s lost through excess fertilizer application.

Fertilizer can be used more efficiently by:¹⁴

• adjusting fertilizer rates to coincide with plant needs
• placing fertilizer near plant roots (but not too deep in the soil)
• applying fertilizers to certain plants, such as turfgrass, twice or more a year, rather than only once¹⁵
• using slow-release forms

Other farming practices that can sometimes reduce NOx emissions on farms include:

• using manure efficiently (less NOx is released from manure)
• using cover crops (sown between successive crops) to remove excess available nitrogen
• adjusting tillage intensity (occasionally, no-till practices can reduce emissions)

Fertilizer isn’t inherently bad for the environment – it’s been used for thousands of years without leaving lasting impacts on the planet.

But using it wisely and taking measures to reduce the impact of NOx pollution from fertilizer is key to making sure that fertilizer can continue to support global agricultural efforts without harming our health.

And if you’re concerned that local agricultural practices are affecting your community’s air quality, go to local city council meetings and make your voice heard.

Individual city governments are often close collaborators with big agricultural companies whose farming practices affect local air pollution, so going straight to the source of your local government’s decision-making can often be the beginning of a huge, positive change.