北京市交通干道空气中CO_2和δ^13C变化及来源分析

Variations of CO_2 concentration and δ^(13)C and source analysis based on stable isotope on a main road of Beijing urban areas

采用离轴积分腔输出光谱技术分析了夏季和冬季北京市四环路空气中CO_2浓度和δ13C值变化特征。结果表明,四环路上车流量大,夏季和冬季均超过15万辆/d,06:00—10:00和15:00—19:00车行缓慢,平均车速小于25 km/h,车道占有率超过60%。机动车排放出大量的CO_2,导致四环路的空气中CO_2浓度呈双峰曲线日变化和δ^(13)C值呈双波谷曲线日变化。同位素定量区分结果显示,四环路空气中CO_2主要来源于机动车尾气排放,夏季和冬季均在52%以上。逐步回归分析表明,平均车速和车道占有率是影响四环路上CO_2浓度和δ13C值的主要因子。06:00—10:00和15:00—19:00来源于汽车尾气的CO_2比例比整个白天来源于汽车尾气的CO_2比例高出6个百分点以上,表明车行缓慢显著增加了CO_2的排放。

Off-axis integrated cavity output spectroscopy was used to measure the CO_2 concentration and stable carbon（ δ^（13）C） isotope ratio in the air around the Fourth Ring Road（ FRR） of Beijing during summer and winter. The result showed that traffic volumes on the FRR were high in both summer and winter,exceeding150 000 per day. The average vehicular velocity was less than 25 km / h,and the occupation rate of the driveway was more than 60% from 06： 00 to 10： 00 and from 15： 00 to 19： 00. The vehicles emitted an enormous amount of CO_2; consequently,the CO_2 concentrations around the FRR during both summer and winter exhibited a two-peak curve. In contrast,diurnal variation in the δ^（13）C value had a two-trough curve. The carbon isotope partitioning result showed that during both summer and winter,atmospheric CO_2 around the FRR was mainly derived from vehicular exhaust and the contribution of vehicular exhaust CO_2 to total CO_2 was over 52%. Stepwise regression analysis indicated that the average velocity and occupancy rate were the main factors affecting the CO_2 concentration and δ^（13）C value around the FRR. Because of traffic trends,the contribution of vehicular exhaust CO_2 to total CO_2 from 06： 00 to 10： 00 and 15： 00 to 19： 00 was 6% higher than that during daytime. The results showed that a lower vehicular velocity significantly increased the emission of CO_2 into the atmosphere.