The role of dew as a night-time reservoir and morning source for atmospheric ammonia
Several field studies have proposed that the volatilization of NH<sub>3</sub> from evaporating dew is responsible for an early morning pulse of ammonia frequently observed in the atmospheric boundary layer. Laboratory studies conducted on synthetic dew showed that the fraction of ammo...
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2016-06-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/16/7435/2016/acp-16-7435-2016.pdf |
| _version_ | 1819179695382462464 |
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| author | G. R. Wentworth J. G. Murphy K. B. Benedict E. J. Bangs J. L. Collett Jr. |
| author_facet | G. R. Wentworth J. G. Murphy K. B. Benedict E. J. Bangs J. L. Collett Jr. |
| author_sort | G. R. Wentworth |
| collection | DOAJ |
| description | Several field studies have proposed that the volatilization of NH<sub>3</sub> from
evaporating dew is responsible for an early morning pulse of ammonia
frequently observed in the atmospheric boundary layer. Laboratory studies
conducted on synthetic dew showed that the fraction of ammonium
(NH<sub>4</sub><sup>+</sup>) released as gas-phase ammonia (NH<sub>3</sub>) during evaporation is
dependent on the relative abundances of anions and cations in the dew. Hence,
the fraction of NH<sub>3</sub> released during dew evaporation (Frac(NH<sub>3</sub>)) can
be predicted given dew composition and pH. Twelve separate ambient dew
samples were collected at a remote high-elevation grassland site in Colorado
from 28 May to 11 August 2015. Average [NH<sub>4</sub><sup>+</sup>] and pH were
26 µM and 5.2 respectively and were on the lower end of dew
[NH<sub>4</sub><sup>+</sup>] and pH observations reported in the literature. Ambient dew
mass (in g m<sup>−2</sup>) was monitored with a dewmeter, which continuously
measured the mass of a tray containing artificial turf representative of the
grass canopy to track the accumulation and evaporation of dew. Simultaneous
measurements of ambient NH<sub>3</sub> indicated that a morning increase in
NH<sub>3</sub> was coincident in time with dew evaporation and that either a
plateau or decrease in NH<sub>3</sub> occurred once the dew had completely
evaporated. This morning increase in NH<sub>3</sub> was never observed on mornings
without surface wetness (neither dew nor rain, representing one-quarter of
mornings during the study period). Dew composition was used to determine an
average Frac(NH<sub>3</sub>) of 0.94, suggesting that nearly all NH<sub>4</sub><sup>+</sup> is
released back to the boundary layer as NH<sub>3</sub> during evaporation at this
site. An average NH<sub>3</sub> emission of 6.2 ng m<sup>−2</sup> s<sup>−1</sup> during dew
evaporation was calculated using total dew volume (<i>V</i><sub>dew</sub>) and
evaporation time (<i>t</i><sub>evap</sub>) and represents a significant morning flux
in a non-fertilized grassland. Assuming a boundary layer height of 150 m,
the average mole ratio of NH<sub>4</sub><sup>+</sup> in dew to NH<sub>3</sub> in the boundary
layer at sunrise is roughly 1.6 ± 0.7. Furthermore, the observed loss
of NH<sub>3</sub> during nights with dew is approximately equal to the observed
amount of NH<sub>4</sub><sup>+</sup> sequestered in dew at the onset of evaporation. Hence,
there is strong evidence that dew is both a significant night-time reservoir
and strong morning source of NH<sub>3</sub>. The possibility of rain evaporation as
a source of NH<sub>3</sub>, as well as dew evaporation influencing species of
similar water solubility (acetic acid, formic acid, and HONO), is also
discussed. If release of NH<sub>3</sub> from dew and rain evaporation is pervasive
in many environments, then estimates of NH<sub>3</sub> dry deposition and NH<sub><i>x</i></sub>
( ≡ NH<sub>3</sub> + NH<sub>4</sub><sup>+</sup>) wet deposition may be overestimated
by models that assume that all NH<sub><i>x</i></sub> deposited in rain and dew remains at
the surface. |
| first_indexed | 2024-12-22T22:02:32Z |
| format | Article |
| id | doaj.art-b52c43960c3749f5b379cffa17a05a36 |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-12-22T22:02:32Z |
| publishDate | 2016-06-01 |
| publisher | Copernicus Publications |
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| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-b52c43960c3749f5b379cffa17a05a362022-12-21T18:11:04ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242016-06-01167435744910.5194/acp-16-7435-2016The role of dew as a night-time reservoir and morning source for atmospheric ammoniaG. R. Wentworth0J. G. Murphy1K. B. Benedict2E. J. Bangs3J. L. Collett Jr.4Department of Chemistry, University of Toronto, 80 St. George Street, M5S 3H6, Toronto, ON, CanadaDepartment of Chemistry, University of Toronto, 80 St. George Street, M5S 3H6, Toronto, ON, CanadaDepartment of Atmospheric Science, Colorado State University, 3915 W. Laporte Ave., 80523, Fort Collins, CO, USADepartment of Atmospheric Science, Colorado State University, 3915 W. Laporte Ave., 80523, Fort Collins, CO, USADepartment of Atmospheric Science, Colorado State University, 3915 W. Laporte Ave., 80523, Fort Collins, CO, USASeveral field studies have proposed that the volatilization of NH<sub>3</sub> from evaporating dew is responsible for an early morning pulse of ammonia frequently observed in the atmospheric boundary layer. Laboratory studies conducted on synthetic dew showed that the fraction of ammonium (NH<sub>4</sub><sup>+</sup>) released as gas-phase ammonia (NH<sub>3</sub>) during evaporation is dependent on the relative abundances of anions and cations in the dew. Hence, the fraction of NH<sub>3</sub> released during dew evaporation (Frac(NH<sub>3</sub>)) can be predicted given dew composition and pH. Twelve separate ambient dew samples were collected at a remote high-elevation grassland site in Colorado from 28 May to 11 August 2015. Average [NH<sub>4</sub><sup>+</sup>] and pH were 26 µM and 5.2 respectively and were on the lower end of dew [NH<sub>4</sub><sup>+</sup>] and pH observations reported in the literature. Ambient dew mass (in g m<sup>−2</sup>) was monitored with a dewmeter, which continuously measured the mass of a tray containing artificial turf representative of the grass canopy to track the accumulation and evaporation of dew. Simultaneous measurements of ambient NH<sub>3</sub> indicated that a morning increase in NH<sub>3</sub> was coincident in time with dew evaporation and that either a plateau or decrease in NH<sub>3</sub> occurred once the dew had completely evaporated. This morning increase in NH<sub>3</sub> was never observed on mornings without surface wetness (neither dew nor rain, representing one-quarter of mornings during the study period). Dew composition was used to determine an average Frac(NH<sub>3</sub>) of 0.94, suggesting that nearly all NH<sub>4</sub><sup>+</sup> is released back to the boundary layer as NH<sub>3</sub> during evaporation at this site. An average NH<sub>3</sub> emission of 6.2 ng m<sup>−2</sup> s<sup>−1</sup> during dew evaporation was calculated using total dew volume (<i>V</i><sub>dew</sub>) and evaporation time (<i>t</i><sub>evap</sub>) and represents a significant morning flux in a non-fertilized grassland. Assuming a boundary layer height of 150 m, the average mole ratio of NH<sub>4</sub><sup>+</sup> in dew to NH<sub>3</sub> in the boundary layer at sunrise is roughly 1.6 ± 0.7. Furthermore, the observed loss of NH<sub>3</sub> during nights with dew is approximately equal to the observed amount of NH<sub>4</sub><sup>+</sup> sequestered in dew at the onset of evaporation. Hence, there is strong evidence that dew is both a significant night-time reservoir and strong morning source of NH<sub>3</sub>. The possibility of rain evaporation as a source of NH<sub>3</sub>, as well as dew evaporation influencing species of similar water solubility (acetic acid, formic acid, and HONO), is also discussed. If release of NH<sub>3</sub> from dew and rain evaporation is pervasive in many environments, then estimates of NH<sub>3</sub> dry deposition and NH<sub><i>x</i></sub> ( ≡ NH<sub>3</sub> + NH<sub>4</sub><sup>+</sup>) wet deposition may be overestimated by models that assume that all NH<sub><i>x</i></sub> deposited in rain and dew remains at the surface.https://www.atmos-chem-phys.net/16/7435/2016/acp-16-7435-2016.pdf |
| spellingShingle | G. R. Wentworth J. G. Murphy K. B. Benedict E. J. Bangs J. L. Collett Jr. The role of dew as a night-time reservoir and morning source for atmospheric ammonia Atmospheric Chemistry and Physics |
| title | The role of dew as a night-time reservoir and morning source for atmospheric ammonia |
| title_full | The role of dew as a night-time reservoir and morning source for atmospheric ammonia |
| title_fullStr | The role of dew as a night-time reservoir and morning source for atmospheric ammonia |
| title_full_unstemmed | The role of dew as a night-time reservoir and morning source for atmospheric ammonia |
| title_short | The role of dew as a night-time reservoir and morning source for atmospheric ammonia |
| title_sort | role of dew as a night time reservoir and morning source for atmospheric ammonia |
| url | https://www.atmos-chem-phys.net/16/7435/2016/acp-16-7435-2016.pdf |
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