Nitrous Oxide (N2O) Emission

Why in news?

Recently, scientists have noted that N2O has higher potential to trap heat compared with CO2.

What do you understand by Nitrous oxide (N2O)?

Nitrous oxide is also called as laughing gas due to the euphoric effects upon inhaling it, a property that has led to its recreational use as a dissociative anaesthetic.

• Properties – At room temperature, it is a colorless non-flammable gas, and has a slightly sweet scent and taste.
• Applications – It has significant medical uses, in surgery and dentistry, for its anesthetic and pain-reducing effects.
• It is used as a propellant, and has a variety of applications from rocketry to making whipped cream.       
• Emissions – Agriculture is one of the main sources of N2O emissions.
• It is produced in the process of nitrification, consisting of the microbial conversion of ammonia to nitrate.
• The amount of N2O produced from the soil through the combined processes of nitrification and denitrification is profoundly influenced by temperature, moisture, carbon, nitrogen and oxygen contents.

Nitrification is a microbial process by which reduced nitrogen compounds (primarily ammonia) are sequentially oxidized to nitrite and nitrate.

Denitrification is the process that converts nitrate to nitrogen gas, thus removing bioavailable nitrogen and returning it to the atmosphere.

What is the current trend of N2O emissions?

• Higher concentration – It’s concentration in the atmosphere reached 336 parts per billion in 2022 (25% above pre-industrial levels).
• Accelerated emission – Accumulation in the atmosphere has accelerated in the last four decades, with growth rates over the past three years (2020-2022) higher than any previous observed year since 1980.
• A total 10 million tonnes of N20 were released into the atmosphere between 1980 and 2020.
• Rise in anthropogenic emission – Global anthropogenic emissions increased by 40% from 1980 to 2020.
• Major sources – Agricultural production contributed 74% of the total anthropogenic N2O emissions in the last decade.
• Soil N2O emissions are increasing due to interactions between nitrogen inputs and global warming, constituting an emerging positive N2O-climate feedback.
• Region-wise assessment – In the 1980s, Europe made the largest contribution to global anthropogenic N2O emissions followed by China and South Asia and the USA.
• From the 1980s to the 2010s, Europe and Russia had the largest decline in the share of anthropogenic N2O emissions, while China and South Asia had the largest increase.

What are the major factors contributing to N2O emissions?

• Soil pH – Alkaline pH enhances the rates of both Nitrification and De-nitrification processes.
• In general, soil pH influences the microbial population and activity, which directly impact N2O emission.

pH is a measure of how acidic/basic water is. The range goes from 0 - 14, with 7 being neutral. pHs of less than 7 indicate acidity, whereas a pH of greater than 7 indicates a base.

• Soil moisture – Moist soils enhance N2O emission over long periods.
• Temperature – Bacterial populations increase with increasing temperature up to a certain range.
• Soil Micro-Organisms – The amount of soil organic carbon positively influences N2O production and emission.
• Even microbes in the oceans releases N2O.
• Other sources – They are also naturally released from tropical rainforests and permafrost melting in the Arctic
• Farming – Increase in farming practices like fertilizer usages increase N2O emissions.
• Tillage disturbs the soil and increases CO2 emission which release the organic carbon that favors microbial activities responsible for GHG emission.
• Application of crop residues – It provides a source of easily available Carbon and Nitrogen, henceforth, a potential source of N2O emission.
• Nitrogen fertilizers – After their application, they enter the soil, undergo diverse reactions resulting in leaching, immobilization and volatilization.
• Non-agricultural human sources – It includes industry processes, biomass and fossil fuel burning, and sewage (waste management).

What are the major challenges associated with N2O?

• Higher lifespan – Its lifetime is over 120 years, much longer than 12 year lifetime of methane, another gas 80 times more harmful than CO2.
• Global warming potential – N2O is the third most important GHG contributing to human-induced global warming, after carbon dioxide (CO2) and methane (CH4).
• It has higher potential to trap heat compared with CO2 and its global warming potential is 300 times more than CO2.

Greenhouse gases (also known as GHGs) are gases in the earth's atmosphere that trap heat.

• Human health – Excess nitrogen leads to soil, water and air pollution, in turn affecting human health and wellbeing.
• Ozone layer depletion – Nitrous oxide has also been implicated in thinning the ozone layer.

What lies ahead?

• Crop Residue Management – The return of Crop Residue can serve as a source of carbon for microbial growth, stimulating the Nitrogen assimilation by micro-organisms.
• Fertilizer management – The containment of Nitrogen doses at the lowest non-limiting levels decreases the soil N availability and, consequently, the N2O emission.
• Biochar Application – It increases soil pH and drives N2O complete reduction to N2, thus curbing N2O emission. 

Biochar is a charcoal-like substance that's made by burning organic material from agricultural and forestry wastes.

• Applications of Lime - It modifies soil pH to reduce the alkalinity of the soil.
• N2O emission decreases linearly with increased pH in a pH range of 4–7, irrespective of soil type.
• Enable Nitrogen sink – An improved inventory of sources and sinks will be required if progress is going to be made toward the objectives of the Paris Agreement. 

References

1. Deccan Herald| Rise in N2O emission due to Fertilizers
2. Global Carbon Project| Global Nitrous Oxide Budget 2024
3. NIH| Management Strategies to Mitigate N2O Emissions