Solubility and reactivity of HNCO in water: insights into HNCO's fate in the atmosphere
A growing number of ambient measurements of isocyanic acid (HNCO) are being made, yet little is known about its fate in the atmosphere. To better understand HNCO's loss processes and particularly its atmospheric partitioning behaviour, we measure its effective Henry's Law coefficient &...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2016-01-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/16/703/2016/acp-16-703-2016.pdf |
| _version_ | 1819061535179276288 |
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| author | N. Borduas B. Place G. R. Wentworth J. P. D. Abbatt J. G. Murphy |
| author_facet | N. Borduas B. Place G. R. Wentworth J. P. D. Abbatt J. G. Murphy |
| author_sort | N. Borduas |
| collection | DOAJ |
| description | A growing number of ambient measurements of isocyanic acid (HNCO) are being
made, yet little is known about its fate in the atmosphere. To better
understand HNCO's loss processes and particularly its atmospheric
partitioning behaviour, we measure its effective Henry's Law coefficient
<i>K</i><sub>H</sub><sup>eff</sup> with a bubbler experiment using chemical
ionization mass spectrometry as the gas phase analytical technique. By
conducting experiments at different pH values and temperature, a Henry's Law
coefficient <i>K</i><sub>H</sub> of 26 ± 2 M atm<sup>−1</sup> is obtained, with an
enthalpy of dissolution of −34 ± 2 kJ mol<sup>−1</sup>, which translates to
a <i>K</i><sub>H</sub><sup>eff</sup> of 31 M atm<sup>−1</sup> at 298 K and at pH 3.
Our approach also allows for the determination of HNCO's acid dissociation
constant, which we determine to be <i>K</i><sub>a</sub> = 2.1 ± 0.2 × 10<sup>−4</sup> M at 298 K. Furthermore, by using ion chromatography to analyze
aqueous solution composition, we revisit the hydrolysis kinetics of HNCO at
different pH and temperature conditions. Three pH-dependent hydrolysis
mechanisms are in play and we determine the Arrhenius expressions for each
rate to be <i>k</i><sub>1</sub> = (4.4 ± 0.2) × 10<sup>7</sup> exp(−6000 ± 240∕<i>T</i>) M s<sup>−1</sup>, <i>k</i><sub>2</sub> = (8.9 ± 0.9) × 10<sup>6</sup> exp(−6770 ± 450∕<i>T</i>) s<sup>−1</sup>
and <i>k</i><sub>3</sub> = (7.2 ± 1.5) × 10<sup>8</sup> exp(−10 900 ± 1400∕<i>T</i>) s<sup>−1</sup>, where <i>k</i><sub>1</sub> is for HNCO + H<sup>+</sup>+ H<sub>2</sub>O → NH<sub>4</sub><sup>+</sup>+ CO<sub>2</sub>, <i>k</i><sub>2</sub> is for HNCO + H<sub>2</sub>O → NH<sub>3</sub>
+ CO<sub>2</sub> and <i>k</i><sub>3</sub> is for NCO<sup>−</sup>+ 2 H<sub>2</sub>O → NH<sub>3</sub>+ HCO<sub>3</sub><sup>−</sup>. HNCO's lifetime against hydrolysis is therefore
estimated to be 10 days to 28 years at pH values, liquid water contents, and
temperatures relevant to tropospheric clouds, years in oceans and months in
human blood. In all, a better parameterized Henry's Law coefficient and
hydrolysis rates of HNCO allow for more accurate predictions of its
concentration in the atmosphere and consequently help define exposure of
this toxic molecule. |
| first_indexed | 2024-12-21T14:44:26Z |
| format | Article |
| id | doaj.art-b285a0cc89f849bcb7777ca3de106df8 |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-12-21T14:44:26Z |
| publishDate | 2016-01-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-b285a0cc89f849bcb7777ca3de106df82022-12-21T19:00:04ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242016-01-011670371410.5194/acp-16-703-2016Solubility and reactivity of HNCO in water: insights into HNCO's fate in the atmosphereN. Borduas0B. Place1G. R. Wentworth2J. P. D. Abbatt3J. G. Murphy4Department of Chemistry, University of Toronto, Toronto, Ontario, CanadaDepartment of Chemistry, University of Toronto, Toronto, Ontario, CanadaDepartment of Chemistry, University of Toronto, Toronto, Ontario, CanadaDepartment of Chemistry, University of Toronto, Toronto, Ontario, CanadaDepartment of Chemistry, University of Toronto, Toronto, Ontario, CanadaA growing number of ambient measurements of isocyanic acid (HNCO) are being made, yet little is known about its fate in the atmosphere. To better understand HNCO's loss processes and particularly its atmospheric partitioning behaviour, we measure its effective Henry's Law coefficient <i>K</i><sub>H</sub><sup>eff</sup> with a bubbler experiment using chemical ionization mass spectrometry as the gas phase analytical technique. By conducting experiments at different pH values and temperature, a Henry's Law coefficient <i>K</i><sub>H</sub> of 26 ± 2 M atm<sup>−1</sup> is obtained, with an enthalpy of dissolution of −34 ± 2 kJ mol<sup>−1</sup>, which translates to a <i>K</i><sub>H</sub><sup>eff</sup> of 31 M atm<sup>−1</sup> at 298 K and at pH 3. Our approach also allows for the determination of HNCO's acid dissociation constant, which we determine to be <i>K</i><sub>a</sub> = 2.1 ± 0.2 × 10<sup>−4</sup> M at 298 K. Furthermore, by using ion chromatography to analyze aqueous solution composition, we revisit the hydrolysis kinetics of HNCO at different pH and temperature conditions. Three pH-dependent hydrolysis mechanisms are in play and we determine the Arrhenius expressions for each rate to be <i>k</i><sub>1</sub> = (4.4 ± 0.2) × 10<sup>7</sup> exp(−6000 ± 240∕<i>T</i>) M s<sup>−1</sup>, <i>k</i><sub>2</sub> = (8.9 ± 0.9) × 10<sup>6</sup> exp(−6770 ± 450∕<i>T</i>) s<sup>−1</sup> and <i>k</i><sub>3</sub> = (7.2 ± 1.5) × 10<sup>8</sup> exp(−10 900 ± 1400∕<i>T</i>) s<sup>−1</sup>, where <i>k</i><sub>1</sub> is for HNCO + H<sup>+</sup>+ H<sub>2</sub>O → NH<sub>4</sub><sup>+</sup>+ CO<sub>2</sub>, <i>k</i><sub>2</sub> is for HNCO + H<sub>2</sub>O → NH<sub>3</sub> + CO<sub>2</sub> and <i>k</i><sub>3</sub> is for NCO<sup>−</sup>+ 2 H<sub>2</sub>O → NH<sub>3</sub>+ HCO<sub>3</sub><sup>−</sup>. HNCO's lifetime against hydrolysis is therefore estimated to be 10 days to 28 years at pH values, liquid water contents, and temperatures relevant to tropospheric clouds, years in oceans and months in human blood. In all, a better parameterized Henry's Law coefficient and hydrolysis rates of HNCO allow for more accurate predictions of its concentration in the atmosphere and consequently help define exposure of this toxic molecule.https://www.atmos-chem-phys.net/16/703/2016/acp-16-703-2016.pdf |
| spellingShingle | N. Borduas B. Place G. R. Wentworth J. P. D. Abbatt J. G. Murphy Solubility and reactivity of HNCO in water: insights into HNCO's fate in the atmosphere Atmospheric Chemistry and Physics |
| title | Solubility and reactivity of HNCO in water: insights into HNCO's fate in the atmosphere |
| title_full | Solubility and reactivity of HNCO in water: insights into HNCO's fate in the atmosphere |
| title_fullStr | Solubility and reactivity of HNCO in water: insights into HNCO's fate in the atmosphere |
| title_full_unstemmed | Solubility and reactivity of HNCO in water: insights into HNCO's fate in the atmosphere |
| title_short | Solubility and reactivity of HNCO in water: insights into HNCO's fate in the atmosphere |
| title_sort | solubility and reactivity of hnco in water insights into hnco s fate in the atmosphere |
| url | https://www.atmos-chem-phys.net/16/703/2016/acp-16-703-2016.pdf |
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