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[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.