A gas chromatographic instrument for measurement of hydrogen cyanide in the lower atmosphere

[摘要] A gas-chromatographic (GC) instrument was developed for measuring hydrogencyanide (HCN) in the lower atmosphere. The main features of the instrumentare (1) a cryogen-free cooler for sample dehumidification and enrichment,(2) a porous polymer PLOT column for analyte separation, (3) a flamethermionic detector (FTD) for sensitive and selective detection, and (4) adynamic dilution system for calibration. We deployed the instrument for a∼4 month period from January–June, 2010 at the AIRMAP atmosphericmonitoring station Thompson Farm 2 (THF2) in rural Durham, NH. A subset ofmeasurements made during 3–31 March is presented here with a detaileddescription of the instrument features and performance characteristics. Thetemporal resolution of the measurements was ~20 min, with a 75 ssample capture time. The 1σ measurement precision was <10% andthe instrument response linearity was excellent on a calibration scale of0.10–0.75 ppbv (±5%). The estimated method detection limit (MDL)and accuracy were 0.021 ppbv and 15%, respectively. From 3–31 March2010, ambient HCN mixing ratios ranged from 0.15–1.0 ppbv (±15%), with a mean value of 0.36 ± 0.16 ppbv (1σ). Theapproximate mean background HCN mixing ratio of 0.20 ± 0.04 ppbv appearedto agree well with tropospheric column measurements reported previously. TheGC-FTD HCN measurements were strongly correlated with acetonitrile(CH₃CN) measured concurrently with a proton transfer-reaction massspectrometer (PTR-MS), as anticipated given our understanding that thenitriles share a common primary biomass burning source to the globalatmosphere. The nitriles were overall only weakly correlated with carbonmonoxide (CO), which is reasonable considering the greater diversity ofsources for CO. However, strong correlations with CO were observed onseveral nights under stable atmospheric conditions and suggest regionalcombustion-based sources for the nitriles. These results demonstrate thatthe GC-FTD instrument is capable of making long term, in-situ measurementsof HCN in the lower atmosphere. To date, similar measurements have not beenperformed, yet they are critically needed to (1) better evaluate theregional scale distribution of HCN in the atmosphere and (2) discern theinfluence of biomass burning on surface air composition in remote regions.

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