Greenhouse gas emitted from vehicles in Seoul megacity, South Korea: Molar ratios (N2O:CO2, CH4:CO2) and stable isotopic compositions of N2O

<p>&#160;Quantifying greenhouse gas (GHG) emissions in the megacities is important to mitigating climate change. To characterize the vehicle emissions which is one of the largest contributors to anthropogenic greenhouse gas emissions, we collected air samples from the entry and exit points of the Sang-do Tunnel in Seoul, South Korea in 2021, and measured dry molar mixing ratios of major greenhouse gases spices emitted from vehicles (CO₂, CH₄, and N₂O). The N₂O:CO₂ emission molar ratio from vehicles is 3.82 &#177; 0.39 &#215; 10^-5, being within a range of 1.8 &#8211; 18.7 &#215; 10^-5 previously reported in Germany, Switzerland, Sweden, and the USA. The CH₄:CO₂ emission molar ratio from the vehicles is 33.52 &#177; 0.43 &#215; 10^-5, which is significantly greater than those observed in Switzerland and the USA of 4.6 &#177; 0.2 &#215; 10^&#8211;5 and 15 &#177; 4 &#215;10^&#8211;5, respectively. Compared with the calculated Further, we also analyzed &#948;¹⁵N and &#948;¹⁸O values of N₂O from the tunnel air. The &#948;¹⁵N and &#948;¹⁸O values of N₂O emitted from the vehicles are estimated as The newly measured data from Seoul may help us better understand greenhouse gas emissions from vehicles in megacities.</p>