[Characteristics of Methane Emission from Urban Traffic in Nanjing]

Urban traffic is an important source of greenhouse gases such as CH₄. The observations on CH₄ are the basis for quantitative analysis of urban carbon emissions. Taken into consideration the weekly and daily changing characteristics of urban traffic, we conducted experiments to analyze the features of traffic CH₄emission and its influential factors. The experiments were conducted on 3 main roads in Nanjing on Oct. 17, 18, 20, 23, 2014 with 5 periods of observation per day, and in Nanjing Yangtze River tunnel in the morning and at night of Sep.11 2014. The results showed that:① The average concentration of CH₄ on the urban main road of Nanjing city was greater than that of the background atmosphere. Affected by traffic conditions, the spatial difference of ΔCH₄ concentration was significant on three typical main roads. ΔCH₄ concentration's diurnal variation showed inverted "W" type, and its peak appeared in the morning and evening rush hours. ② Due to the "piston wind" in the tunnel, the CH₄ concentration in Nanjing Yangtze River tunnel gradually increased from the inlet to the outlet and the difference of concentration between the inlet and the outlet was 0.21×10^-6-0.38×10^-6. ③ There was a good linear correlation between CH₄ concentration and CO₂ concentration. The atmospheric ΔCH₄:ΔCO₂ value of urban main road in Nanjing was 0.0091 and the atmospheric ΔCH₄:ΔCO₂ value of Nanjing Yangtze River Tunnel was 0.00047-0.0014. ④ Traffic volume and the proportion of natural gas vehicles were the main factors influencing atmospheric ΔCH₄ concentration and ΔCH₄:ΔCO₂.