大气非甲烷烃在线测量系统的研发与应用

Development and application of an online measuring system for ambient nonmethane hydrocarbons

为满足大气非甲烷烃(NMHCs)时空分布监测需求,开发出一套可用于移动观测的小型在线测量系统.环境空气经Teflon膜去除颗粒物后,以100 m L·min-1流速采样进入多床吸附剂捕集阱,样品气中的NMHCs在-10℃的温度下被捕集,之后,捕集阱经高纯氮气反吹后迅速升温至300℃,载气(高纯氮气)以1.6 m L·min-1将解吸出的样品送入GC-FID进行检测.通过系列条件实验,确定了吸附剂的最佳组合和仪器运行的最优参数,在此条件下,本系统最低检出限为0.01 nmol·mol-1(顺-2-丁烯),标准工作曲线R2为0.9991~0.9998,10次重复实验RSD<3%.本系统与现有商业化设备TH-300B的测量结果具有较好的一致性,在实际外场应用中,运行稳定性高、能准确追踪12种典型NMHCs的大气浓度变化,可为定量分析大气二次污染形成机制提供关键前体物信息.

To address the crucial need for temporal and spatial observation of ambient Non-Methane Hydrocarbon （ NMHCs）, we developed a compact online system which can be deployed for mobile measurement. Ambient air is sampled at a flow rate of 100 mL. min-l into the system. A Teflon filter is used in front of the sampling line for removing particles. NMHCs in the air sample is trapped at -10 ℃ by a cryo-cooled multi-bed adsorbent trap. After sampling, the analytes are thermally desorbed at 300℃ and transferred into a GC-FID by purified nitrogen gas （N2 ） at a flow rate of 1.6 mL. min-l for speciation and quantification. Based on a number of conditional experiments, we determined the best combination of different adsorbents as well as operating parameters of the system. Under the best chosen working condition, the LOD of the system is 0.01 nmol .tool-1 for eis-2-butene, the R2 of standard curves for 56 VOCs are between 0.9991 and 0.9998, and the RSD of 10 repetitive trials is less than 3%. Good agreement of NMHCs measurement results are found between this system and a commercial instrument TH-300B. During a field observation, the system was running with high stability and was accurately tracking the variation of 12 typical NMHCs in the atmosphere, which demonstrates the capability of the system in providing key information for quantitatively analyzing the formation mechanism of secondary air pollution.