Evaluation of offline sampling for atmospheric C3-C11 non-methane hydrocarbons

Junfeng Liu , Zhiguo Liu , Chengtang Liu , Zhouming He , Yujing Mu , Chenglong Zhang , Yuanyuan Zhang , Pengfei Liu , Yuzheng Wang


Received February 04, 2021,Revised , Accepted May 14, 2021, Available online June 23, 2021

Volume 34,2022,Pages 132-140

The concentration variation of C3-C11 non-methane hydrocarbons (NMHCs) collected in several types of commercial flexible bags and adsorption tubes was systematically investigated using a gas chromatography-flame ionization detector (GC-FID) system. The percentage loss of each NMHC in the polyvinyl fluoride (PVF) bags was less than 5% during a 7-hr storage period; significant NMHCs loss was detected in aluminum foil composite film and fluorinated ethylene propylene bags. The thermal desorption efficiency of NMHCs for adsorption tubes filled Carbopack B and Carboxen1000 sorbents was greater than 95% at 300℃, and the loss of NMHCs in the adsorption tubes during 20-days storage at 4℃ was less than 8%. The thermal desorption efficiency for C11 NMHCs in the adsorption tube filled with Carbograph 1 and Carbosieve SⅢ absorbents was less than 40% at 300℃, and pyrolysis of the absorbents at 330℃ interfered significantly with the measurements of some alkenes. The loss of alkenes was significant when NMHCs were sampled by cryo-enrichment at -90℃ in the presence of O3 for the online NMHC measurements, and negligible for enrichment using adsorption tubes at 25℃. Although O3 scrubbers have been widely used to eliminate the influence of O3 on NMHC measurements, the loss of NMHCs with carbon numbers greater than 8 was more than 10%. Therefore, PVF bags and adsorption tubes filled Carbopack B and Carboxen1000 sorbents were recommended for the sampling of atmospheric NMHCs.

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