Greenhouse Gas Profile: Nitrous Oxide

Intro

In Earth’s atmosphere, nitrogen is four times more abundant than the oxygen we breathe. As a greenhouse gas nitrous oxide (N2O), is about 300 times more effective at trapping and radiating infrared energy than carbon dioxide. Like other greenhouse gasses, N2O’s molecular structure makes it very effective at trapping and emitting infrared energy. N2O exists as part of Earth’s nitrogen cycle, so it may take on many forms before being emitted into the atmosphere. N2O is also colorless and odorless, making it difficult to track accurately. Once N2O makes it into the atmosphere, it can take up to 100 years to break into its basic components.

According to the EPA, about 75% of N2O emissions come from the agriculture sector. Agricultural N2O emissions result primarily from manure and excessive fertilizer use, which eventually leaves the farm through runoff and other means. Other sources of N2O come from microbial activity in the oceans and fossil fuel combustion.

Keep in mind that N2O will take on many different forms through the nitrogen cycle, so for the sake of simplicity, N2O emissions may be lumped in under the parent base, nitrogen (N) and nitrogen gas (N2). Read on for more details on N2O sources, sinks, and solutions.

Sources of N2O

Both terrestrial and oceanic nitrogen emissions are driven primarily by microbial activity. Microorganisms produce various forms of nitrogen (N) as a byproduct of their metabolic processes. Nitrification and denitrification are two major mechanisms that microorganisms use to transform nitrogen compounds.

Agriculture Fertilizers

Nitrogen (N), Phosphorus (P), and Potassium (K) are common ingredients in organic and synthetic fertilizers. Applying fertilizer introduces more nutrients into the soil to improve crop growth, health, and yield. Overfertilization accounts for about 1/3rd of nitrous oxide(N2O) emissions from agriculture.

Denitrification/ Volitilization

The volatilization of nitrogen fertilizer into nitrogen gas happens rapidly. This is why about 50% of any nitrogen applied to crops will be lost to the air in a week. Rain and strong winds may exacerbate nutrient losses. Denitrification/Volitization accounts for about 1/3rd of nitrous oxide(N2O) emissions from agriculture

Plant uptake through Nitrification

Plants grow in part from the nitrogen they consume from the soil. NO3 is the form of nitrogen that is consumable for plants. Nitrifying bacteria help generate NO3 for plants by processing Ammonium (NH4) from the soil, A.K.A Nitrification.

Erosion, runoff, and leaching

Nitrogen is fairly soluble in water. During rain and irrigation events, nitrogen may be carried away with the water. Erosion describes nitrogen that is abrased from the soil. Runoff refers to nitrogen removed by water as it runs over the soil’s surface. Leaching accounts for the dissolved nitrogen carried deep into the soil.

Mineralization

The conversion of organic plant-usable Nitrogen into inorganic Ammonium (NH4) as microorganisms decompose organic matter for energy.

Biological Waste (poop)

Ammonia (NH3) is a component of biowaste that volatilizes into nitrogen gas (N2) when exposed to open air. For nitrogen emissions related to agriculture, raising livestock contributes to 2 thirds of those emissions. To reduce nitrogen emissions and the impact of manure on air quality, researchers have proposed a variety of potential solutions, including but not limited to:

Deep, capped, manure storage

Manure is a massive source of Ammonia. Improving how manure is stored would significantly reduce the volume of Nitrogen-related emissions from agriculture. Researchers found that mass adoption of underground storage tanks, away from the open air, would help slash Ammonia emissions by about 80%.

Manure Trading

Infrastructure that allows farmers to trade excess manure and compost with other farms would help to develop and first-world countries alike. Networking between livestock and crop-based farms would help them take advantage of organic soil amendments and reduce their dependence on synthetic fertilizers.

Crop Application and scheduling

Colorado has an early warning system that alerts livestock farmers about weather patterns that are prone to carrying away Ammonia. Warning systems like this could help farmers schedule fertilizer application days in a way that mitigates nutrient loss and nitrogen emissions.

Reduce the protein content in livestock feed

In general, animals are not perfectly efficient systems. Researchers found that protein that exceeds the daily needs of livestock tends to result in increased nitrogen in their waste.

Oceans

The ocean has a complex system for circulating nitrogen. Consider the general process a continuation of the terrestrial nitrogen cycle. Fish produce Ammonia (NH3) through their waste, which may volatilize and escape into the air. Microorganisms take (N2) and convert it into ammonia (NO3) for phytoplankton and other marine flora to consume.

Chemical manufactruring

N2O is a byproduct of synthesizing nitric acid, a key ingredient in commercial fertilizers. The same goes for Adipic acid, a component of nylon production and other synthetic fibers.

Fossil fuel combustion

Nitrous oxide (N2O) is released when fossil fuels are burned. The amount of N2O emitted depends on the type of fossil fuel being burned.

Sinks of N2O

Lakes, streams, and the ocean

The ocean is the largest pool of nitrogen on Earth. Because nitrogen is especially dissolvable in water, the oceans’ surface and the atmosphere exchange nitrogen-based compounds regularly. Nitrogen may also enter the ocean as runoff from inland sources like agriculture.

The nitrogen cycle that occurs in the intermediate and deep ocean makes use of the ammonia and decomposing material from fish. Through denitrification and nitrification, the toxic ammonia from waste is converted into Nitrates (NO3), nitrous oxide (N2O), and nitrogen gas (N2).

Soil and Vegitation

The second-largest nitrogen sink on Earth is in the soil and in the plants that grow from it. Nitrogen gets into the soil through a mechanism known as nitrogen fixation. This describes the nitrification phase of the nitrogen where microorganisms synthesize nitrate (NO3), the form of nitrogen that plants may grow from.

The Atmosphere

Nitrogen is much more abundant than oxygen in the atmosphere. While it is non-toxic, you would never want to breathe in our nitrogen because it displaces oxygen in the lungs and will suffocate you. Regardless, the atmosphere is composed of about 78% Nitrogen (N2), 21%oxygen, 0.9% Argon (Ar), and 0.1% other gasses like Carbon Dioxide (CO2), Methane (CH4), and water vapor (H2O).