南京城市交通甲烷排放特征

Characteristics of Methane Emission from Urban Traffic in Nanjing

城市交通是CH_4等温室气体的重要排放源,而CH_4排放的观测研究是定量分析城市碳排放的基础.本项研究考虑城市交通的周变化和日变化特点,于2014年10月17日、18日、20日、23日每日5个时段在南京市主城区三条交通主干道上和2015年9月11日的早晚时段在南京长江隧道内,观测大气CH_4和CO_2浓度,分析交通CH_4排放特征及其影响因素.结果表明:1南京城区交通主干道的CH_4平均浓度均大于背景大气CH_4浓度.受交通车流量的影响,ΔCH_4浓度的空间差异显著.ΔCH_4浓度的日变化呈现倒"W"型,在交通早晚高峰时出现峰值.2由于隧道内"活塞风"的作用,长江隧道内的CH_4浓度从入口到出口逐渐增大,出入口浓度差在0.21×10-6~0.38×10-6(摩尔分数,下同)之间.3大气CH_4浓度与CO_2浓度之间线性相关.交通主干道上的ΔCH_4∶ΔCO_2值平均为0.009 1;隧道内的ΔCH_4∶ΔCO_2值仅为0.000 47~0.001 4.4影响南京城区道路大气ΔCH_4浓度和ΔCH_4∶ΔCO_2值的主要因素分别是车流量和天然气车占车流量的比例.

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 CH4 emission 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： ①The 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 △CH4 concentration was significant on three typical main roads. △CH4 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 . ③There was a good linear correlation between CH4 concentration and CO2 concentration. The atmospheric △CH4： △CO2 value of urban main road in Nanjing was 0. 009 1 and the atmospheric △CH4 ： △CO2 value of Nanjing Yangtze River Tunnel was 0. 000 47-0. 001 4. ④Traffic volume and the proportion of natural gas vehicles were the main factors influencing atmospheric △CH4 concentration and △CH4： △CO2 .