Chemical consequences of mixing atmospheric droplets of varied pH

Perdue, Edward M.; Beck, Kevin C.

doi:10.1029/jd093id01p00691

Cited by 39 publications

(10 citation statements)

References 8 publications

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“…Thus, in the case of the 1986 samples, the measured fog water pH might not represent the acidity of the individual droplets in equilibrium with the surrounding atmosphere. This effect has also been reported by Jacob et al (1986b) for the case of NH,(g)/NHZ equilibrium in fog-water solutions and has been discussed by Perdue and Beck (1988). Of course, no comment can be made as yet regarding acetic acid, due to the lack of data at higher pH.…”

Section: Resultssupporting

confidence: 65%

Organic acid gas and liquid-phase measurements in Po Valley fall-winter conditions in the presence of fog

Winiwarter¹,

Puxbaum²,

Fuzzi³

et al. 1988

Tellus B

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Concurrent gas and liquid phase organic acid measurements during radiation fog episodes are reported. Gas phase concentrations of HCOOH and CH3COOH exhibit large variations from the detection limit (5 nmol 0.1 ppb) to 150 nmol m-3 (3.5 ppb). Liquid phase concentration ranges of 11-175 and 10-269 p M were observed for HCOOH and CH,COOH, respectively. Large deviations from Henry's law equilibrium were observed for HCOOH when the pH of fog droplet solutions was above 5. Our hypothesis is that in this range, the bulk sample pH might not be representative of the acidity of individual droplets in equilibrium with the gas phase. The organic acids in the Po Valley fall-winter conditions seem to originate from anthropogenic processes

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Section: Resultssupporting

confidence: 65%

Organic acid gas and liquid-phase measurements in Po Valley fall-winter conditions in the presence of fog

Winiwarter¹,

Puxbaum²,

Fuzzi³

et al. 1988

Tellus B

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“…It is also unlikely that the implicit assumption in our calculations of an internal mixture of particles is the source of the discrepancy. For example, Perdue and Beck [1988] found that when an external mixture of cloud drops in equilibrium with a collection of trace gases are collected in a bulk sample, the resulting sample will be supersaturated with respect to the existing trace composition. However, in our calculations we found an apparent undersaturation with respect to NH 3 .…”

Section: Results and Analysismentioning

confidence: 99%

“…During such long sampling periods, there can be significant variations in the ambient gas‐ and particulate‐phase composition, as well as the ambient temperature and relative humidity. Since the equilibrium partitioning between the gas and particulate phases of individual parcels of air can generally be quite different from the equilibrium partitioning obtained by mixing these parcels together [ Perdue and Beck , 1988], the equilibrium predicted on the basis of the average conditions over a sampling periods will not necessarily reproduce the actual partitioning even though equilibrium may apply to each of the individual parcels. This fact along with the susceptibility of filter‐based techniques to artifacts [ Chow , 1995; Weber et al , 2001; Slanina et al , 1992, 2001] raises some question as to the accuracy of these studies.…”

Section: Introductionmentioning

confidence: 99%

An evaluation of the thermodynamic equilibrium assumption for fine particulate composition: Nitrate and ammonium during the 1999 Atlanta Supersite Experiment

Zhang¹,

Chameides²,

Weber³

et al. 2002

J. Geophys. Res.

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[1] Data obtained during the 1999 Atlanta Supersite Experiment are used to test the validity of the assumption of thermodynamic equilibrium between fine particulate (PM 2.5 ) nitrate (NO 3 À ) and ammonium (NH 4 + ) and gas-phase nitric acid (HNO 3 (g)) and ammonia (NH 3 (g)). Equilibrium is tested by first calculating the equilibrium concentrations of HNO 3 (g) and NH 3 (g) implied by the PM 2.5 inorganic composition (i.e, Na + , NH 4 + , Cl À , NO 3 À , and SO 4 2À ), temperature, and relative humidity observed at the site. These calculated equilibrium concentrations are then compared to the corresponding observed gas-phase concentrations. The observed PM 2.5 composition is based on the 5-min averaged measurements of the Georgia Tech PILS [Weber et al., 2001], while the observed HNO 3 (g) and NH 3 (g) concentrations are based on the measurements of Edgerton et al. [2000a] and Slanina et al. [2001], respectively. The equilibrium gas-phase concentrations are calculated using the ISORROPIA model of Nenes et al. [1998]. Out of the entire Atlanta Supersite database, we were able to identify 272 five-minute intervals with overlapping measurements of PM 2.5 composition, HNO 3 (g) and NH 3 (g). Initial calculations using these 272 data points suggest an absence of thermodynamic equilibrium with the calculated equilibrium NH 3 (g) generally less than its observed concentration and predicted HNO 3 (g) generally greater than the observed concentration. However, relatively small downward adjustments in the measured PM 2.5 SO 4 2À (or apparent acidity) bring the calculated and measured NH 3 (g) and HNO 3 (g) into agreement. Moreover, with the exception of 31 of the 272 data points with either anomalously low observed concentrations of SO 4 2À or NH 3 (g), there is a close correspondence between the SO 4 2À (or acidity) correction needed for HNO 3 and that needed for NH 3 (slope of 1.04, intercept of $0, and r 2 = 0.96). The average relative corrections required for equilibrium with HNO 3 and NH 3 are À14.1% and À13.7%, respectively; significantly larger than the estimated uncertainty arising from random errors in the measurement. One interpretation of our results is that thermodynamic equilibrium does in fact apply to the inorganic PM 2.5 composition during the Atlanta Supersite Experiment and either (1) the PM 2.5 SO 4 2À concentration measured by the PILS was systematically overestimated by $15% or (2) the PM 2.5 PILS systematically underestimated the concentration of the alkaline components by $15%; and/or 3. The ISORROPIA model systematically underestimated the pH of the PM 2.5 encountered during the experiment.

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“…For example, Jacob (1986) listed well over 100 reactions in the chemical specification of his model, but for the microphysical specification simply assumed that the cloud droplets were monodisperse and instantaneously assumed a fixed (10 gm) radius upon imposition of a specified, instantaneous temperature decrease. A possible deficiency in this approach is that the consequences of nonlinearities in droplet chemistry as a function of size, such as those illustrated by Perdue and Beck (1988), cannot be treated in this type of model.…”

Section: Introductionmentioning

confidence: 99%

Numerical study of droplet size dependent chemistry in oceanic, wintertime stratus cloud at southern mid-latitudes

Ayers

Larson

1990

J Atmos Chem

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Cloud droplet chemistry is modelled for the first 150 m of rise m a wintertime, midlatitude, marine stratus cloud using observations made at and near the Cape Grim Baseline Station as a source of input parameters. The emphasis in this work was to study the variation in droplet chemistry as a function of both droplet size and nucleus composition, with a particular focus on the way in which oxidation of dissolved sulfur dioxide varied.At 150 na above the condensation level, solute concentration as a function of droplet size was found to increase by as much as 2 to 3 orders of magnitude for only a factor of 2 increase in droplet radius, primarily as a consequence of the I/r dependence in the droplet growth equation. This type of size dependence exists at all levels in the model cloud, and has a significant influence on oxidation rate of sulfur dioxide in droplets growing on 'sulfate' nuclei, oxidation by ozone being favoured in the smallest droplets, but oxidation by hydrogen peroxide being favoured in the larger droplets. Oxidation by ozone is favoured at all sizes in droplets formed on sea-salt nuclei as a result of the initially high alkalinity of these droplets, and in the cloud overall is calculated to be the more important oxidation pathway. Although based on a simplified chemical scheme, these results suggest that both size-dependent and nucleus-dependent chemistry of cloud droplets may need to be considered explicitly in cloud modelling work.Volume-weighted mean pH values in the range 5 to 6 were predicted from sensitivity studies in which input variables were varied over reasonable ranges, in agreement with two sets of bulk cloudwater pH data obtained by aircraft near Cape Grim.

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Chemical consequences of mixing atmospheric droplets of varied pH

Cited by 39 publications

References 8 publications

Organic acid gas and liquid-phase measurements in Po Valley fall-winter conditions in the presence of fog

Organic acid gas and liquid-phase measurements in Po Valley fall-winter conditions in the presence of fog

An evaluation of the thermodynamic equilibrium assumption for fine particulate composition: Nitrate and ammonium during the 1999 Atlanta Supersite Experiment

Numerical study of droplet size dependent chemistry in oceanic, wintertime stratus cloud at southern mid-latitudes

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