Among greenhouse gases, nitrous oxide (N₂O) is considered one of the most harmful agents for climate change. According to the IPCC's 6th Assessment Report (AR6), the global warming potential (GWP) of N₂O over 100 years is 273 times higher than that of CO₂ (IPCC AR6, 2021). This means that even a small amount of N₂O emissions can contribute significantly to global warming, making it especially important to control and calculate this gas. Let's learn how to calculate it with GREEN IN N2O emission factor in the content below!
Legal basis and calculation instructions
To ensure consistency and transparency in greenhouse gas inventories, especially N₂O, many countries now adopt specific guidelines and legal frameworks.
Internationally, the most widely referenced document is the IPCC Greenhouse Gas Inventory Guidelines (IPCC Guidelines). The 2006 guidelines and their 2019 update provide emission factors (EFs) for key emission sectors such as agriculture, industry, energy and waste management. This is a standard data source, helping countries to agree on calculation methods and to compare results between national reports.
In Vietnam, the legal basis related to the N2O Emission Factor is specifically regulated in the following documents:
- Law on Environmental Protection 2020: Fully regulate the responsibility for reducing greenhouse gas (GHG) emissions and integrate this issue into socio-economic development policies.
- Decree 06 / 2022 / ND-CP on GHG emission reduction and ozone layer protection: Specify the requirement to conduct periodic GHG inventories and apply emission factors appropriate to national conditions.
- Circular 01/2022/TT-BTNMT GHG inventory technical specifications: Provide specific guidance on calculation methods, including the use of IPCC default emission factors or published national factors.
- Decision 2626/QD-BTNMT (2022) of the Ministry of Natural Resources and Environment: Official announcement of national emission factors for GHG inventory, including specific factors for N₂O in sectors such as agriculture, energy and waste treatment.
N2O emission factor according to IPCC and Vietnam
N2O emission factors are prescribed by the IPCC and countries as a basis for calculating greenhouse gas inventories. These factors are built on scientific research and practical data, and may vary depending on geographical conditions, soil, technology and production processes.
IPCC default emission factors
In the IPCC 2006 Guidelines and the 2019 Refinement update, the default N2O Emission Factors are divided by main sectors:
Agriculture:
- Direct N₂O emissions from agricultural soils when applying synthetic or organic fertilizers: 1% of the amount of nitrogen applied to the soil will be emitted as N₂O (EF = 0,01 kg N₂O-N/kg N).
- Indirect emissions from nitrate leaching and ammonia volatilization are also assigned separate coefficients.
Energy:
- The combustion of fossil fuels produces N₂O with a coefficient that depends on the fuel type and combustion technology (e.g., coal, oil, natural gas, biomass).
- Default emission levels range from 0,001–0,015 kg N₂O/GJ (IPCC, 2006).
Industry:
- Production of nitric acid, adipic acid, caprolactam and glyoxal is the main source of N₂O.
- Default EF of nitric acid production: 0,003–0,005 t N₂O/t product (IPCC, 2019).
Waste:
- Municipal and industrial wastewater treatment also generates N₂O, with a default EF of approximately 0,005 kg N₂O-N/kg N in wastewater.
N2O emission factor in Vietnam
Vietnam has officially announced the emission factors for GHG inventory in Decision 2626/QD-BTNMT (2022). In particular, the N2O emission factors have been localized according to domestic production and environmental conditions, including:
- Agriculture: EF N₂O directly from fertilization of agricultural land: 0,0075 kg N₂O-N/kg N (lower than IPCC default, due to different growing conditions and fertilizer use efficiency).
- Energy: EF N₂O from coal combustion: 0,0015 kg N₂O/GJ; from DO oil: 0,0006 kg N₂O/GJ; from natural gas: 0,0001 kg N₂O/GJ.
- Waste: EF N₂O from domestic wastewater treatment: 0,0045 kg N₂O-N/kg N (close to IPCC factor).
Comparison with some ASEAN countries
- Thailand: EF N₂O directly from agricultural land according to BUR3 report (2020) still keeps IPCC default 0,01 kg N₂O-N/kg N.
- Indonesia: Applying the same EF as IPCC in agriculture, but with a lower adjustment for waste treatment (0,004 kg N₂O-N/kg N).
- Malaysia: Using EF IPCC 2006 for most sectors, but is studying localization factor for palm oil industry.
Thus, Vietnam is one of the early ASEAN countries to announce its own national emission factor for N₂O, which helps to better reflect reality than just applying the default of IPCC, while increasing the reliability of N2O emission factor inventory reports and building emission reduction policies.
Method for calculating N2O emission factor
Basic formula (general form):
N₂O emissions = Activity (or applied N amount) × Emission factor
Depending on the data source and inventory goal, the formula can be written specifically in terms of many variables (e.g. kg N applied to soil × EF N₂O directly; or fuel amount × EF N₂O for energy…).
IPCC calculation levels (Tier):
- Tier 1 (default): Uses IPCC default emission factors (simple, data-poor); suitable for rough estimates or when detailed data are lacking.
- Tier 2 (national/industry data): Use adjusted or calculated emission factors at the national/sector level (more reflective of local specificities).
- Tier 3 (measurement data/detailed model): Based on direct observation, biological/soil modeling, or source-specific measurements; most accurate but resource-intensive.
Example: Calculate N2O emission factor from 100 tons of urea fertilizer (apply default Tier 1/IPCC)
Step 1: Determine the amount of nitrogen (N) in 100 tons of urea
- Mass of urea = 100 tons = 100.000 kg.
- Urea has an N content of ≈ 46% (0,46).
=> N (kg) = 100.000 kg × 0.46 = 46.000 kg N
Step 2: Apply direct emission factors (IPCC Tier 1)
The IPCC gives a direct emission factor of 0,01 kg N₂O-N / kg N (i.e. 1% of the applied N becomes N₂O-N).
=> N₂O-N (kg) = 46.000 kg N × 0.01 = 460 kg N₂O-N
Step 3: Convert from N₂O-N to N₂O
Mass ratio N₂O / N₂O-N = 44/28 ≈ 1,5714286.
=> N₂O (kg) = 460 kg N₂O-N × (44/28) ≈722.857 kg N₂O
=> Results (direct emissions according to Tier 1): ~722,86 kg N₂O.
Step 4: Convert to CO₂e (Optional)
Using GWP₁₀₀ of N₂O according to IPCC AR6 = 273
=> CO₂e (kg) = 722.857 × 273 ≈ 197.340 kg CO₂e ≈ 197.34 t CO₂e
=> From 100 t urea (46.000 kg N) ⇒ direct emissions ≈ 0,723 t N₂O ⇒ equivalent to ≈ 197,3 t CO₂e (GWP₁₀₀ = 273).
Note:
- The above example calculates direct N₂O emissions. The IPCC also includes indirect emissions (due to NH₃ volatilization and nitrate leaching/runoff) — these sources are then added to the indirect N₂O using appropriate formulas and factors (the IPCC has corresponding f_factors and EFs).
- At Tier 2, you can replace the 0.01 coefficient with a national coefficient, reflecting domestic growing conditions.
- At Tier 3, using soil-air models (or field observations) to estimate N use efficiency, weather conditions, soil management… gives more accurate results.
- When officially reporting in Vietnam, it is necessary to comply with Circular 01/2022/TT-BTNMT, Decree 06/2022/ND-CP and refer to Decision 2626/QD-BTNMT (2022) on emission factors for GHG inventory.
Conclusion
In general, businesses, management agencies, and communities that master the method of calculating and accurately using the N2O Emission Factor will contribute to providing practical solutions to reduce emissions in agriculture, industry, energy, and waste treatment.