Effect of mixed-phase cloud on the chemical budget of trace gases: A modeling approach

International audienceA multiphase cloud chemistry model coupling a detailed chemical reactivity mechanism in gas phase and aqueous phase to a cloud parcel model with a two-moment microphysical scheme has been extended to include ice phase processes. This newly developed model is used to study the influence of the ice phase on HCOOH, HNO3, H2O2 and CH2O in a mixed-phase cloud. Microphysical processes are describing the interactions between the water vapor phase, the liquid phase (cloud and rain water) and the ice phase (pristine ice, snow and graupel) in the cloud and for soluble chemical species, their transfer by mixed-phase microphysical processes has been included. In addition to microphysical transfer between iced hydrometeors, the probable two main processes incorporating soluble chemical species in iced hydrometeors are the retention in ice phase as riming or freezing occurs and the burial in the ice crystal as the crystal grows by vapor diffusion. The model is applied to a cloud event describing a moderate precipitating mixed-phase cloud forming in a continental air mass in winter. The main features of the cloud are described and the evolution of key chemical species as function of time and temperature is discussed. Sensitivity tests are performed: a run without ice to highlight the influence of ice phase on the chemical gas phase composition of the cloud, a run without burial showing that it is a negligible process, a run assuming full retention in ice for all species and a run varying the ice crystal shapes. A detailed analysis of the microphysical rates and chemical rates linked to retention and burial effects show that for this cloud event, the effect of the ice phase on gas phase composition is driven by riming of cloud droplets onto graupels, which leads to retention or not of soluble chemical species in the ice phase. Finally, the impact of crystal geometry on the efficiency of collection is studied together with its impact on the riming of cloud droplets on graupels and also on the retention of chemical species in ice phase

Numerical quantification of sources and phase partitioning of chemical species in cloud: Application to wintertime anthropogenic air masses at the Puy de Dôme station

International audienceThe Model of Multiphase Cloud Chemistry M2C2 has recently been extended to account for nucleation scavenging of aerosol particles in the cloud water chemical composition. This extended version has been applied to multiphase measurements available at the Puy de Dôme station for typical wintertime anthropogenic air masses. The simulated ion concentrations in cloud water are in reasonable agreement with the experimental data. The analysis of the sources of the chemical species in cloud water shows an important contribution from nucleation scavenging of particles which prevails for nitrate, sulphate and ammonium. Moreover, the simulation shows that iron, which comes only from the dissolution of aerosol particles in cloud water, has a significant contribution in the hydroxyl radical production. Finally, the simulated phase partitioning of chemical species in cloud are compared with measurements. Numerical results show an underestimation of interstitial particulate phase fraction with respect to the measurements, which could be due to an overestimation of activated mass by the model. However, the simulated number scavenging efficiency of particles agrees well with the measured value of 40% of total number of aerosol particles activated in cloud droplets. Concerning the origin of chemical species in cloud water, the model reproduces quite well the contribution of gas and aerosol scavenging estimated from measurements. In addition, the simulation provides the contribution of in-cloud chemical reactivity to cloud water concentrations

Modelisation du transport et de la redistribution des especes chimiques tropospheriques: physicochimie humide a moyenne echelle

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : TD 20452 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Modeling study of strong acids formation and partitioning in a polluted cloud during wintertime

International audienceA multiphase chemistry model coupled with a quasi-spectral microphysical model has been applied to measurements from the European Cloud Ice Mountain Experiment campaign to quantify the formation of the strong acids nitrate and sulfate and to evaluate the role of microphysical processes in redistributing reactive species among the different phases (gas versus cloud and/or rain). Significant formation of nitrate and sulfate are found to be due to the reaction of pernitric acid with the sulfite ion. Moreover, pernitric acid, because of its equilibrium in the gas phase and its high solubility, is always available both in cloud water and in rainwater via mass transfer from the gas phase. The sulfite ion comes from the mass transfer from the gas phase of sulfur dioxide in cloud water. When rain formation begins, it is efficiently transferred to the rainwater by collision/coalescence processes. This leads to an enhancement in strong acid production when microphysics is activated in the model. Modeled results have been compared with experimental data in an effort to retrieve a behavior law related to the partitioning between the gas and aqueous phases of the cloud. In particular, when collision/coalescence processes are considered, an improvement in retrieving the partitioning of soluble species and especially nitrate is observed. A higher production in sulfate could help interpret the discrepancy of global model calculations with observed sulfate concentrations in Europe in wintertime

Paramétrisation des processus physico-chimiques de formation des nuages et étude de leurs impacts sur l'évolution de la composition chimique atmosphérique

Ce travail porte sur le développement d'un module microphysique de nuages liquides et glacés dans un modèle de chimie multiphase (Leriche et al., 2001). Le modèle complet a été appliqué afin d'évaluer le rôle de ces nuages sur les teneurs en polluants atmosphériques. Les nuages modulent le transport horizontal et vertical des polluants ainsi que leur lessivage via les précipitations, ils sont aussi le siège de réactions chimiques complexes. En paramétrisant la répartition des polluants entre les différentes phases du nuage via des processus comme le givrage, la croissance des cristaux par dépôt de vapeur, la fonte et la collection des hydrométéores, il est montré l'importance de la phase glace et de la morphologie des cristaux dans l'évolution chimique du nuage. Des scénarios de formation nuageuse sont définis à partir de masses d'air continentale et / ou marine, pour voir l'influence de la capacité du nuage à précipiter sur la composition chimique des hydrométéores. Des tests sur la rétention et l'enfouissement pilotant les échanges avec la phase glacée lors du givrage et de la croissance par dépôt de vapeur respectivement ont été menés pour conclure au rôle majeur joué par la glace dans le bilan des espèces tracesCLERMONT FD-BCIU Sci.et Tech. (630142101) / SudocSudocFranceF

Preface - Special Issue CIME

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Etude de l'activation des noyaux de condensation (mesure, analyse et développement instrumental)

CLERMONT FD-BCIU Sci.et Tech. (630142101) / SudocSudocFranceF

Effects of Different Rain Parameterizations on the Simulation of Mesoscale Orographic Precipitation

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Air Pollution Modeling and Its Application XII

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Impact of radical versus non-radical pathway in the Fenton chemistry on the iron redox cycle in clouds

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