Nitrous oxide and methane emissions and nitrous oxide isotopic composition from waste incineration in Switzerland

Highlights: • N₂O emissions from waste incineration with SNCR NO_x removal are 51.5 ± 10.6 g t⁻¹. • This is significantly lower than the reported Swiss emission factor of 120 g t⁻¹ (FOEN, 2013). • N₂O contributes <0.3% and ≈2.5% of GHG emissions from SCR and SNCR plants. • Measured isotopic SP of 17.7‰ is likely characteristic for N₂O emissions from SNCR. • CH₄ emitted by waste incineration is negligible, contributing <0.01% to total GHGs. - Abstract: Solid waste incineration accounts for a growing proportion of waste disposal in both developed and developing countries, therefore it is important to constrain emissions of greenhouse gases from these facilities. At five Swiss waste incineration facilities with grate firing, emission factors for N₂O and CH₄ were determined based on measurements of representative flue gas samples, which were collected in Tedlar bags over a one year period (September 2010–August 2011) and analysed with FTIR spectroscopy. All five plants burn a mixture of household and industrial waste, and two of the plants employ NO_x removal through selective non-catalytic reduction (SNCR) while three plants use selective catalytic reduction (SCR) for NO_x removal. N₂O emissions from incineration plants with NO_x removal through selective catalytic reduction were 4.3 ± 4.0 g N₂O tonne⁻¹ waste (wet) (hereafter abbreviated as t⁻¹) (0.4 ± 0.4 g N₂O GJ⁻¹), ten times lower than from plants with selective non-catalytic reduction (51.5 ± 10.6 g N₂O t⁻¹; 4.5 ± 0.9 g N₂O GJ⁻¹). These emission factors, which are much lower than the value of 120 g N₂O t⁻¹ (10.4 g N₂O GJ⁻¹) used in the 2013 Swiss national greenhouse gas emission inventory, have been implemented in the most recent Swiss emission inventory. In addition, the isotopic composition of N₂O emitted from the two plants with SNCR, which had considerable N₂O emissions, was measured using quantum cascade laser spectroscopy. The isotopic site preference of N₂O – the enrichment of ¹⁴N¹⁵NO relative to ¹⁵N¹⁴NO – was found to be 17.6 ± 0.8‰, with no significant difference between the two plants. Comparison to previous studies suggests SP of 17–19‰ may be characteristic for N₂O produced from SNCR. Methane emissions were found to be insignificant, with a maximum emission factor of 2.5 ± 5.6 g CH₄ t⁻¹ (0.2 ± 0.5 g CH₄ GJ⁻¹), which is expected due to high incinerator temperatures and efficient combustion