Modeling of scavenging processes in clouds: some remaining questions about the partitioning of gases among gas and liquid phases

doi:10.1016/S0169-8095(99)00041-1

Atmospheric Research

Volume 53, Issues 1–3, March 2000, Pages 29-43

https://doi.org/10.1016/S0169-8095(99)00041-1 Get rights and content

Abstract

Clouds can play an important role by affecting the chemical composition of the troposphere through modification of photolysis rates, and by redistributing compounds through the vertical transport of species and their removal by wet deposition and finally by aqueous phase chemical reactions within cloud water or precipitation water. Several examples of the effects of clouds on tropospheric chemistry are shown, using a box model or a mesoscale model illustrating the role of clouds on hydrogen peroxide: its partitioning between the gas and aqueous phases, including deviations from Henry's law. The main results are that deviations from Henry's law exist even for small droplets, which are located on the edges of orographic clouds while equilibrium is attained in the center of the cloud. The partitioning of gases is a function of the cloud development conditions such as the air mass in which the cloud has been formed (continental vs. maritime), the microphysical properties (cloud water content, rainwater content).

Introduction

More than 50% of the Earth's surface is covered by clouds and theoretical calculations of Ravishankara (1997) have shown that clouds can alter the chemical composition of the atmosphere on a global scale. Clouds interact in many ways with chemicals on a wide range of scales, from micrometers up to thousands of kilometers.

On a large scale (thousands of kilometers), clouds are organized in broad and complex systems that are responsible for the transport of species from the boundary layer to the free troposphere Renard et al., 1994, Edy et al., 1996. Tracer redistribution can be greatly changed in case of precipitating clouds systems due to their efficient scavenging. Photochemical processes can be modified through cloud/radiation interactions (Thompson, 1984). Within these systems, each individual cloud is the host of complex microphysical processes that influence the partitioning of species among the air, the cloud and the precipitation (Grégoire et al., 1994). Finally, on microscale level, gas absorption and chemical reactions greatly depend on the microstructure of the cloud such as the droplet spectrum. Therefore, one has to consider complex interfacial transfer between gaseous and liquid phases Wurzler et al., 1995, Ricci et al., 1997.

Moreover, these small scale features cannot be ignored at larger scales because removal processes and radiative properties of clouds that perturb photochemistry depend on the microphysical characteristics of the clouds (Madronich, 1987).

In order to simulate such complex interactions on the whole range of scales at which they are important, it is necessary to use several types of models from box chemical model, to mesoscale models.

In this paper, scavenging processes that occur in clouds and their dependency on the fine microphysical features, such as droplet size, liquid water content will be discussed for one particular chemical species, hydrogen peroxide, which is both a soluble and a reactive compound in clouds. The way clouds interact with this particular species will be described in details. In particular, deviations from Henry's law can occur in clouds for this species at the sudden apparition of the aqueous phase or in a cloud, presenting different types of granulometry (cloud droplets vs. raindrops).

Section snippets

Non equilibrium kinetics: mass-transfer of H₂O₂ between gas and liquid phases

The rate equation in gaseous phase for a particular species may be written as: $d C_{g} d t =P_{g} −L_{g} C_{g}$ where P_g and L_g are respectively the production and destruction terms and C_g the gaseous concentration of the species.

With the introduction of cloud water, this equation becomes: $d C_{g} d t =P_{g} −L_{g} C_{g} −Lk_{t} C_{g} + k_{t} C_{aq} H_{eff} RT$ where k_t describes the mass transfer between the gas and aqueous phases, L the liquid water content, H_eff the Henry's law effective constant of the species (Schwartz, 1986) and C_aq the aqueous

Deviations from Henry's law for hydrogen peroxide during a cloud lifetime

The evolution of hydrogen peroxide has been followed during a cloud event by means of a chemical box model (Madronich and Calvert, 1990), which interprets any chemical mechanism, including aqueous phase chemistry based upon Grégoire et al. (1994). The chemical system is a standard gas phase mechanism including methane and CO in the presence of NO_x and sulfur dioxide. The pH is held constant, equal to 4. Table 1, Table 2, Table 3, Table 4, Table 5 list the reactions, the initial concentrations

Deviations from Henry's law for hydrogen peroxide in a polydisperse cloud

The same type of study (Audiffren et al., 1996) has been performed in the framework of a mesoscale model simulating orographic clouds formed from different air masses (continental vs. maritime). This mesoscale meteorological model is coupled with the chemical module described in Section 3, except that the chemical equation system is solved with a QSSA type solver more appropriate (see Audiffren et al., 1998 for more details). A complete description of the meteorological mountain wave scenario

Conclusion

In this study, several examples of liquid clouds have been simulated by two types of models: a process model and a mesoscale model, including the multiphase chemistry. Experimentally, it is still very difficult to isolate concentrations of chemical species in one particular phase. Moreover, most of the time, samplings of cloud chemistry are based on measurements from pluviometers or impactors that provide time-integrated results, or low-sensitivity airborne measurements. Within the models, it

Acknowledgements

The work reported in this paper was supported by the INSU/CNRS (Institut National des Sciences de l'Univers/Centre National de La Recherche Scientifique) Program PNCA (Programme National de Chimie Atmosphérique). The first authors are very grateful to ADEME and Electricité de France for their support. Computer resources were provided by I.D.R.I.S. (Institut du Développement et Des Ressources en Informatique Scientifique), project no. 187.

References (29)

N. Audiffren et al.
Deviations from the Henry's law equilibrium during cloud events: a numerical approach of the mass transfer between phases and its specific numerical effects
Atmos. Res.
(1998)
N. Chaumerliac et al.
Acidity production in orographic clouds and rain in a mesoscale model with semi-spectral microphysics
Atmos. Environ.
(1990)
N. Audiffren et al.
Effects of a polydisperse cloud on tropospheric chemistry
J. Geophys. Res.
(1996)
E.X. Berry et al.
An analysis of cloud drops growth by collection: II. Single initial distributions
J. Atmos. Sci.
(1974)
N. Chaumerliac et al.
Sulfur scavenging in a mesoscale model with quasi-spectral microphysics: two-dimensional results for continental and maritime clouds
J. Geophys. Res.
(1987)
W.B. De More
Chemical kinetics and photochemical data for use in stratospheric modeling
JPL Publ No. 94-26
(1987)
J. Edy et al.
Modeling ozone and carbon monoxide redistribution by shallow convection over the amazonian rain forest
J. Geophys. Res
(1996)
S. Fuzzi
P.J. Grégoire et al.
Impact of cloud dynamics on tropospheric chemistry: advances in modeling the interactions between microphysical and chemical processes
J. Atmos. Chem.
(1994)
N. Huret et al.
Impact of different microphysical schemes on the dissolution of highly and less soluble non-reactive gases by cloud droplets and raindrops
J. Appl. Meteor.
(1994)

J.V. Iribarne et al.

Models of cloud chemistry

Tellus

(1989)

Laj, P., Fuzzi, S., Facchini, M.C., Lind, J.A., Orsi, G., Preiss, M., Maser, R., Jaeschke, W., Seyffer, E., Helas, G.,...

J. Lelieveld et al.

The role of clouds in tropospheric photochemistry

J. Atmos. Chem.

(1991)

S. Madronich

Photodissociation in the atmosphere: I. Actinic flux and the effects of ground reflections and clouds

J. Geophys. Res.

(1987)

Cited by (17)

The contribution of site to washout and rainout: Precipitation chemistry based on sample analysis from 0.5mm precipitation increments and numerical simulation
2014, Atmospheric Environment
Citation Excerpt :
The estimates in the present analysis agree with the previous estimates at all three sites. The washout contribution in the urban site (Kobe City) was greater than that at the other two sites; this is attributed to the fact that the HNO3(g) concentration in urban ambient air was higher than that in rural ambient air (Aikawa et al., 2008b) due to the strong emission intensity of the precursor gas NOx (NO + NO2) and susceptibility of HNO3(g) to the gas-washout process (Encinas and Casado, 1999; Kasper-Gieble et al., 1999; Chaumerliac et al., 2000; Voisin et al., 2000; Encinas et al., 2004). Fig. 5 shows the distributions of SO42− concentrations for successive increments of precipitation received within discrete rainfall events for each of the three sites.
Datasets of precipitation chemistry at a precipitation resolution of 0.5 mm from three sites were studied to determine whether the washout and rainout mechanisms differed with site type (urban, suburban, rural). Rainout accounted for approximately one-third of the total NO₃⁻ deposition and washout contributed two-thirds, irrespective of the site type, although the washout contribution at the urban site (over 70%) was larger than that at the other two sites. The rainout mechanism and the washout mechanism both accounted for about half the total SO₄²⁻ deposition at the suburban and rural sites, whereas at the urban site the rainout contribution was over 80%. A chemical transport model produced similar levels of washout and rainout contributions as the precipitation chemistry data.
Cell model of in-cloud scavenging of highly soluble gases
2013, Journal of Atmospheric and Solar-Terrestrial Physics
Citation Excerpt :
Scavenging of soluble gases by single evaporating droplets was analyzed by Elperin et al. (2007, 2008). In-cloud scavenging of highly-soluble gases was investigated by Levine and Schwartz (1982), Wurzler et al. (1995), Wurzler (1998), Chaumerliac et al. (2000). Levine and Schwartz (1982) assumed that soluble gas scavenging by cloud droplets is governed by physical absorption.
We investigate mass transfer during absorption of highly soluble gases such as HNO₃, H₂O₂ by stagnant cloud droplets in the presence of inert admixtures. Thermophysical properties of the gases and liquids are assumed to be constant. Diffusion interactions between droplets, caused by the overlap of depleted of soluble gas regions around the neighboring droplets, are taken into account in the approximation of a cellular model of a gas–droplet suspension whereby a suspension is viewed as a periodic structure consisting of the identical spherical cells with periodic boundary conditions at the cell boundary. Using this model we determined temporal and spatial dependencies of the concentration of the soluble trace gas in a gaseous phase and in a droplet and calculated the dependence of the scavenging coefficient on time. We found that scavenging coefficient for gas absorption by cloud droplets remains constant and sharply decreases only at the final stage of absorption. In the calculations we employed a Monte Carlo method and assumed gamma size distribution of cloud droplets. It is shown that despite of the comparable values of Henry's law constants for the hydrogen peroxide (H₂O₂) and the nitric acid (HNO₃), the nitric acid is scavenged more effectively by cloud droplets than the hydrogen peroxide due to a major affect of the dissociation reaction on HNO₃ scavenging. It is demonstrated that scavenging of highly soluble gases by cloud droplets leads to strong decrease of soluble trace gas concentration in the interstitial air. We obtained also analytical expressions for the “equilibrium values” of concentration of the soluble trace gas in a gaseous phase and for concentration of the dissolved gas in a liquid phase for the case of hydrogen peroxide and nitric acid absorption by cloud droplets.
Modeling studies of the sulfur cycle in low-level, warm stratiform clouds
2006, Atmospheric Research
A one-dimensional cloud model with size-resolved microphysics has been fully coupled with size-resolved aqueous-phase chemistry. The model, driven by prescribed dynamics, has been used to study the sulfur cycle in low-level, warm stratiform clouds. Model evaluation and sensitivity tests show that the model can reasonably simulate the time-evolution of cloud properties, interstitial aerosols, gas to aqueous conversions and size-resolved cloud water acidity.
Model results show that gaseous NH₃ and H₂O₂ can be removed quickly by the aqueous-phase process within the cloud layer due to the very small size of cloud droplets. 10% to 50% of SO₂ within the cloud layer can be scavenged in a 1-h period depending on the concentrations of other gaseous species, especially those of NH₃ and H₂O₂. Aqueous-phase chemistry can effectively transfer mass from gas to aqueous particles in low-level, warm stratiform clouds. The rate of transfer from gaseous SO₂ to aqueous sulfate depends on the cloud properties, which are controlled by the initial cloud condensation nuclei (CCN) from which the cloud forms, and on gaseous concentrations of other species such as NH₃ and H₂O₂. Aqueous-phase chemistry might broaden the cloud droplet spectra by increasing the number concentrations of both smallest and largest droplets, and thus enhance precipitation formation.
SPACCIM: A parcel model with detailed microphysics and complex multiphase chemistry
2005, Atmospheric Environment
Multiphase processes, such as the uptake of gases by clouds or the production of gas phase halogens from particulate halides are of increasing importance for the understanding of the tropospheric system. Mass transfer and chemical reactions modify the concentrations of stable compounds and oxidants in either phase. The parcel model SPACCIM is presented which combines a complex multiphase chemical model with a detailed microphysical model. For this purpose, a new coupling scheme is implemented. The description of both components is given for a fine-resolved particle/drop spectrum. The SPACCIM approach allows the coupling of multiphase chemical models with microphysical codes of various types. An efficient numerical solution of such systems is only possible utilizing the special structure. An implicit time-integration scheme with an adapted sparse solver for the linear systems is applied. Its numerical efficiency and robustness is analyzed for two scenarios and versions of different complexity of the multiphase chemistry mechanism CAPRAM. The sensitivity of simulation results against variations in the particle/droplet size resolution, the coupling time step and numerical control parameters is discussed. Guidelines for an “optimal” choice of control parameters are derived from this sensitivity study. The coupling scheme operation is always robust and reliable. Model simulations are compared with several measurements from the FEBUKO field campaign. Simulated and measured results show a reasonable agreement.
Comparison of different model approaches for the simulation of multiphase processes
2005, Atmospheric Environment
Cloud-chemistry models are developed intensively with increasing complexity, leading to new knowledge and offering new possibilities to understand the physico-chemical processes taking place in the atmosphere. Intercomparing such detailed models is the way to test the robustness and reliability of their parameterizations and numerical schemes. The present study involves newly developed parcel models treating microphysics and chemistry with equal rigor. The description of both kinds of processes is given for a size-resolved particle/droplet spectrum. Three different types of models are compared. In the spaccim approach, one- and two-dimensional particle/drop microphysical schemes are used in a time-splitting setup between chemistry and microphysics. The galerkin model employs a one-dimensional scheme in a fully coupled setup. For each of the three types, “fixed bin” and “moving bin” approaches are implemented. A comparison between “fixed” and “moving bin” approaches makes sense only for scenarios without coagulation and breakup. The paper focuses on the effects of different microphysical and numerical approaches on the multiphase chemistry. The resulting changes in the particle/droplet composition feed back on cloud microphysics. Substantiated conclusions can only be derived if these effects are studied for a wide range of cases. Thus, the simulations are performed for three chemical reaction mechanisms of different complexity and four scenarios derived from field measurements. The interaction between numerical schemes, microphysics and multiphase chemistry is discussed. Mostly, the results of the participating models agree in an appreciable way. Observable differences are noticed between the “moving bin” approach and models using fixed grids for the discretization of the particle/droplet spectrum. Furthermore, the initial aerosol composition influences the fate of chemical species as well as the behavior of the numerical solver in a substantial way.
Time-integration of multiphase chemistry in size-resolved cloud models
2002, Applied Numerical Mathematics
The existence of cloud drops leads to a transfer of chemical species between the gas and aqueous phases. Species concentrations in both phases are modified by chemical reactions and by this phase transfer. The model equations resulting from such multiphase chemical systems are nonlinear, highly coupled and extremely stiff. In the paper we investigate several numerical approaches for treating such processes. The droplets are subdivided into several classes. This decomposition of the droplet spectrum into classes is based on their droplet size and the amount of scavenged material inside the drops, respectively. The very fast dissociations in the aqueous phase chemistry are treated as forward and backward reactions. The aqueous phase and gas phase chemistry, the mass transfer between the different droplet classes among themselves and with the gas phase are integrated in an implicit and coupled manner by the second order BDF method. For this part we apply a modification of the code LSODE with special linear system solvers. These direct sparse techniques exploit the special block structure of the corresponding Jacobian. Furthermore we investigate an approximate matrix factorization which is related to operator splitting at the linear algebra level. The sparse Jacobians are generated explicitly and stored in a sparse form. The efficiency and accuracy of our time–integration schemes is discussed for four multiphase chemistry systems of different complexity and for a different number of droplet classes.

View all citing articles on Scopus

View full text

Modeling of scavenging processes in clouds: some remaining questions about the partitioning of gases among gas and liquid phases

Abstract

Introduction

Section snippets

Non equilibrium kinetics: mass-transfer of H2O2 between gas and liquid phases

Deviations from Henry's law for hydrogen peroxide during a cloud lifetime

Deviations from Henry's law for hydrogen peroxide in a polydisperse cloud

Conclusion

Acknowledgements

Atmos. Res.

Atmos. Environ.

Effects of a polydisperse cloud on tropospheric chemistry

J. Geophys. Res.

An analysis of cloud drops growth by collection: II. Single initial distributions

J. Atmos. Sci.

Sulfur scavenging in a mesoscale model with quasi-spectral microphysics: two-dimensional results for continental and maritime clouds

J. Geophys. Res.

Chemical kinetics and photochemical data for use in stratospheric modeling

JPL Publ No. 94-26

Modeling ozone and carbon monoxide redistribution by shallow convection over the amazonian rain forest

J. Geophys. Res

Impact of cloud dynamics on tropospheric chemistry: advances in modeling the interactions between microphysical and chemical processes

J. Atmos. Chem.

Impact of different microphysical schemes on the dissolution of highly and less soluble non-reactive gases by cloud droplets and raindrops

J. Appl. Meteor.

Models of cloud chemistry

Tellus

The role of clouds in tropospheric photochemistry

J. Atmos. Chem.

Photodissociation in the atmosphere: I. Actinic flux and the effects of ground reflections and clouds

J. Geophys. Res.

Non equilibrium kinetics: mass-transfer of H₂O₂ between gas and liquid phases