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Temperature dependence of Henry's law constant for hydrogen cyanide. Generation of trace standard gaseous hydrogen cyanide.

ABSTRACT: Primary data for the temperature dependent solubility of HCN in water do not presently exist for low concentrations of HCN at environmentally or physiologically relevant temperatures. Henry's Law constant (K(H), M/atm) for the vapor-solution equilibrium of HCN was determined in 0.1 M sodium phosphate buffer (adjusted to pH 9.00 +/- 0.03 at 296.6 +/- 0.1 K) from 287-311 K. Stable gas phase concentrations of HCN are generated by established techniques, via air equilibration of aqueous cyanide partitioned by a microporous membrane. The effluent gaseous HCN, in equilibrium with the constant temperature aqueous cyanide, was collected in dilute NaOH and determined by a spectrophotometrically using cobinamide. The K(H) of HCN may be expressed as ln K(H) (M/atm) = (8205.7 +/- 341.9)/T - (25.323 +/- 1.144); r(2) = 0.9914) where T is the absolute temperature in K. This corresponds to 9.02 and 3.00 M/atm at 25 and 37.4 degrees C, respectively, compared to actual measurements of 9.86 and 3.22 at 25.0 and 37.8 degrees C, respectively. The technique also allows for convenient generation of trace levels of HCN at ppbv-ppmv levels that can be further diluted.

SUBMITTER: Ma J

PROVIDER: S-EPMC2855313 | biostudies-literature | 2010 Apr

REPOSITORIES: biostudies-literature

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Temperature dependence of Henry's law constant for hydrogen cyanide. Generation of trace standard gaseous hydrogen cyanide.

Ma Jian J Dasgupta Purnendu K PK Blackledge William W Boss Gerry R GR

Environmental science & technology 20100401 8

Primary data for the temperature dependent solubility of HCN in water do not presently exist for low concentrations of HCN at environmentally or physiologically relevant temperatures. Henry's Law constant (K(H), M/atm) for the vapor-solution equilibrium of HCN was determined in 0.1 M sodium phosphate buffer (adjusted to pH 9.00 +/- 0.03 at 296.6 +/- 0.1 K) from 287-311 K. Stable gas phase concentrations of HCN are generated by established techniques, via air equilibration of aqueous cyanide part ...[more]

PMID: 20302333

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Project description:The dry deposition process refers to flux loss of an atmospheric pollutant due to uptake of the pollutant by the Earth's surfaces, including vegetation, underlying soil, and any other surface types. In chemistry transport models (CTMs), the dry deposition flux of a chemical species is typically calculated as the product of its surface layer concentration and its dry deposition velocity (V d); the latter is a variable that needs to be highly empirically parameterized due to too many meteorological, biological, and chemical factors affecting this process. The gaseous dry deposition scheme of Zhang et al. (2003) parameterizes V d for 31 inorganic and organic gaseous species. The present study extends the scheme of Zhang et al. (2003) to include an additional 12 oxidized volatile organic compounds (oVOCs) and hydrogen cyanide (HCN), while keeping the original model structure and formulas, to meet the demand of CTMs with increasing complexity. Model parameters for these additional chemical species are empirically chosen based on their physicochemical properties, namely the effective Henry's law constants and oxidizing capacities. Modeled V d values are compared against field flux measurements over a mixed forest in the southeastern US during June 2013. The model captures the basic features of the diel cycles of the observed V d. Modeled V d values are comparable to the measurements for most of the oVOCs at night. However, modeled V d values are mostly around 1 cm s-1 during daytime, which is much smaller than the observed daytime maxima of 2-5 cm s-1. Analysis of the individual resistance terms and uptake pathways suggests that flux divergence due to fast atmospheric chemical reactions near the canopy was likely the main cause of the large model-measurement discrepancies during daytime. The extended dry deposition scheme likely provides conservative V d values for many oVOCs. While higher V d values and bidirectional fluxes can be simulated by coupling key atmospheric chemical processes into the dry deposition scheme, we suggest that more experimental evidence of high oVOC V d values at additional sites is required to confirm the broader applicability of the high values studied here. The underlying processes leading to high measured oVOC V d values require further investigation.

Dataset Information

Temperature dependence of Henry's law constant for hydrogen cyanide. Generation of trace standard gaseous hydrogen cyanide.

Publications

Temperature dependence of Henry's law constant for hydrogen cyanide. Generation of trace standard gaseous hydrogen cyanide.

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