A Three-Dimensional Modeling Study of the Effects of Solidphase Hydrometeor Chemical Interactions in Cumulonimbus Clouds on Tropospheric Chemical Distributions (original) (raw)

Chemistry and physics of a winter stratus cloud layer: A case study

Journal of Geophysical Research, 1987

The chemical and physical properties of a supercooled stratus cloud layer and surrounding clear air covering southern Ontario on February 20, 1984, were studied with the objectives of identifying the processes responsible for the cloud water chemical composition. The cloud layer, which extended from circa 650 to 1050 m mean sea level, was bounded by a strong temperature inversion just at cloud top. The air below this inversion was well mixed vertically, as indicated by the near independence of concentrations of various trace gas species with altitude and by conservation of number concentration of particles from the surface to cloud top, with below-cloud aerosol number concentrations (0.2 < d < 3 #m) approximately equal to the sum of the interstitial aerosol and cloud droplet (2 < d < 30 #m) number concentrations. Fractional incorporation of aerosol sulfate into cloud water, determined by comparison of interstitial and cloud water sulfate concentrations, was in the range of 85-90%, similar to the result inferred from comparison of interstitial aerosol and cloud droplet number concentrations. Gas phase equivalent concentrations of cloud water species were the same (within experimental error) as the concentrations of aerosol and soluble trace gas species in the below-cloud air. These results suggest that the dominant processes determining cloud water composition in this cloud layer were nucleation scavenging of sulfate aerosol and scavenging of gaseous HNO 3, with no significant contribution from reactive scavenging processes. ple, HNO3) present prior to cloud formation, and (3) reactive scavenging, whereby sparingly soluble gases react in cloud to form soluble compounds that are retained in the cloud water.

A Modeling Study of the Influence of Ice Scavenging on the Chemical Composition of Liquid-Phase Precipitation of a Cumulonimbus Cloud

Journal of Applied Meteorology, 1999

Evidence of the efficient removal of chemicals by ice particles has been deduced from past field experiments and laboratory studies. However, the ice phase has been poorly represented in prior cloud chemistry modeling. This paper uses a two-dimensional Eulerian cloud model to address the impact of ice-phase processes on the chemistry of precipitation in the context of a simulated cumulonimbus cloud. Riming of graupel and the freezing of supercooled rain are the main processes for the transfer of species toward graupel. Even when freezing is the main mode for this transfer, riming still plays an important role by providing a feedback effect that limits the diluting influence of rain. When riming is the only process, sulfate production is more efficient in rainwater, whereas when freezing dominates a decrease in sulfate production is observed. During the decaying stage, the precipitation (glaciated and/or liquid) has higher concentrations of the hydrogen peroxide and sulfates that originated from the gas phase. However, sulfates chemically produced in the liquid phases are less concentrated than if ice had played no role. This study demonstrates the potential impact of ice-phase processes in organized cloud systems where strong updrafts exist, as ahead of a cold front.

The Influence of Cloud Processes on the Distribution of Chemical Species for the 10 July 1996 STERAO/Deep Convection Storm

2000

Clouds are able to modify the distribution of chemical species in many ways Through air motions associated with clouds chemical species are trans ported from the boundary layer to the free tropo sphere Highly soluble species may dissolve into the cloud water and rain and ultimately be deposited on the ground in the precipitation Because of the inter action of the cloud hydrometeors chemical species may be captured by the precipitating ice particles Photolysis rates are altered by the scattering and at tenuation of solar radiation The cloud hydromete ors may serve as locations for aqueous and ice phase reactions Deep convection is usually thought to transport insoluble chemical species from the boundary layer to the upper troposphere and to rain out highly soluble species By using a non hydrostatic three dimensional convective cloud model coupled to a simple chemical reaction mechanism we examine the importance of aqueous chemistry microphysical processes and modi ed photolysis rates...

The relationships among cloud microphysics, chemistry, and precipitation rate in cold mountain clouds

Atmospheric Environment, 2000

A study was conducted to examine the relationships among air pollutant loadings, cloud microphysics, and snowfall rates in cold mountain clouds. It was hypothesized that variations in pollutant loadings would be re#ected in shifts in the cloud droplet size distribution. A "eld program was conducted at Storm Peak Laboratory (SPL) at an elevation of 3210 m MSL in northwestern Colorado. Cold precipitating clouds were sampled during January, 1995. Cloud water was collected and analyzed for major ion and trace element chemistry. Cloud droplet concentrations and size were measured continuously using a PMS FSSP-100. The results indicate a direct relationship between clear-air equivalent (CAE) sulfate concentrations in cloud water and cloud droplet concentrations, an indirect relationship between droplet number and droplet size, a direct relationship between droplet size and snowfall rate, and an indirect relationship between CAE sulfate concentration and snowfall rate.

Estimating the impact of natural and anthropogenic emissions on cloud chemistry: the influence of organic compounds

Atmospheric Chemistry and Physics Discussions, 2004

In order to estimate the anthropogenic influence of gas and aerosol emissions from the Petroleum Industry in maritime zones with clouds of small vertical extent, a numerical 1D Eulerian cloud-chemical model with detailed microphysics (Alfonso and Raga, 2002) is used to simulate the influence of water soluble organic compounds (WSOC) and organic+inorganic gas emissions on cloud development. Following Mircea et al. (2002), we tested the sensitivity of the cloud and precipitation development in the classical inorganic case (CIC) and the inorganic+organic case (IOC) with respect to CCN compositions. The results indicate an increase in the droplet concentration for the IOC, and a delay in the development of precipitation. The pH spectral evolution was studied during both the development and precipitation stages. The influence of the diffusion of formic acid and its generation by oxidation of hydrated formaldehyde in the aqueous phase result in a reduction in the pH of precipitation in th...

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

Atmospheric Research, 2010

A 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, HNO 3 , H 2 O 2 and CH 2 O in a mixedphase 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.

A relationship between liquid water content and chemical composition in clouds

Atmospheric Research, 1996

In this paper we present two-year results from the Cloud Chemistry Measurements Programme, carried out at Mr. Brocken/Harz (Germany) to assess the influence of cloud physical parameters on the chemical composition of clouds. There are large variations in the chemical composition of cloud water. We found that the liquid water content of clouds predominantly determines the ionic content. The relationship is best approximated by a power function, nearly identical for all chemical species. We identified deviations of data points from the general relationship accompanying events with different air pollution situations. An important conclusion is that cloud chemistry monitoring in the sense of air pollution studies is meaningless without measurement of cloud physical parameters. These are liquid water content, cloud base altitudes, and to some extent, droplet size distribution.

The influence of organic compounds on the development of precipitation acidity in maritime clouds

Atmospheric Chemistry and Physics, 2004

In order to estimate the anthropogenic influence of gas and aerosol emissions from the Petroleum Industry in maritime zones with clouds of small vertical extent, a numerical 1-D Eulerian cloud-chemical model with detailed microphysics (Alfonso and Raga, 2002) is used to simulate the influence of water soluble organic compounds (WSOC) and organic+inorganic gas emissions on cloud development. Following Mircea et al. , we tested the sensitivity of the cloud and precipitation development in the classical inorganic case (CIC) and the inorganic+organic case (IOC) with respect to CCN compositions. The results indicate an increase in the droplet concentration for the IOC, and a delay in the development of precipitation.

Global cloud and precipitation chemistry and wet deposition: tropospheric model simulations with ECHAM5/MESSy1

Atmospheric Chemistry and Physics, 2007

The representation of cloud and precipitation chemistry and subsequent wet deposition of trace constituents in global atmospheric chemistry models is associated with large uncertainties. To improve the simulated trace gas distributions we apply the new submodel SCAV, which includes detailed cloud and precipitation chemistry and present 5 results of the atmospheric chemistry general circulation model ECHAM5/MESSy1. A good agreement with observed wet deposition fluxes for species causing acid rain is obtained. The new scheme enables prognostic calculations of the pH of clouds and precipitation, and these results are also in accordance with observations. We address the influence of detailed cloud and precipitation chemistry on trace constituents based 10 on sensitivity simulations. The results confirm previous results from regional scale and box models, and we extend the analysis to the role of aqueous phase chemistry on the global scale. Some species are directly affected through multiphase removal processes, and many also indirectly through changes in oxidant concentrations, which in turn have an impact on the species lifetime. While the overall effect on tropospheric 15 ozone is relatively small (<10%), regional effects on O 3 can reach ∼20%, and several important compounds (e.g., H 2 O 2 , HCHO) are substantially depleted by clouds and precipitation. 25 (Rasch et al., 2000). These uncertainties are to a large extent associated with the 786 ACPD 7, 785-848, 2007 Abstract Introduction Conclusions References Tables Figures Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion