Sulfur chemistry in the National Center for Atmospheric Research Community Climate Model: Description, evaluation, features, and sensitivity to aqueous chemistry

Abstract

Abstract.Sulfur chmnistry has been incorporated in the National Center [or Atmospheric Research Community Climate Model in an internally consistent manner with other parameterizations in the model. The model predicts mixing ratios of dimethylsulfide (DMS), SO2, SO•-, H202. Processes that control the mixing ratio of these species include the emissions of DMS and SO2, transport of each species, gas-and aqueous-phase chemistry, wet deposition, and dry deposition of species. Modeled concentrations agree quite well with observations for DMS 2-and H202, fairly well for SO2, and not as well for SO42--. The modeled SO4 tends to underestimate observed SO•-at the surface and overestimate observations in the upper troposphere. The SO2 and SO•-species were tagged according to the chernical production pathway and whether the sulfilr was of anthropogenic or biogenic origin. Although aqueous-phase reactions in cloud accounted for 81% of the sulfate production rate, only ,.050-60% of the sulfatc burden in the troposphere was derived from cloud chemistry. Because cloud chemistry is an important source of sulfate in the troposphere, the importance of H•O2 concentrations and pH values was investigated. When prescribing H202 concentrations to clear-sky values instead of predicting H202, the global-averaged, annual-averaged in-cloud production ot • sulfate increased. Setting the pH of the drops to 4.5 also increased the in-cloud production of sulfatc. In both sensitivity simulations, the increased in-cloud production of sulfate decreased the burden of sulfate because less SO2 was available for gas-phase conversion, which contributes •nore efficiently to the tropospheric sulfate burden than does aqueous-phase conversion.

Influences of in-cloud aerosol scavenging parameterizations on aerosol concentrations and wet deposition in ECHAM5-HAM

“…This simplistic approach has been used in global models (Barth et al, 2000). We find that the global and annual mean aerosol mass burdens in simulation F100 are lower in comparison to the CTL simulation, by up to 10% for sulfate.…”

“…100% of the aerosols in clouds are assumed to be scavenged into the droplets or crystals for the simulation F100. This simplistic assumption has been used in global models (e.g., Barth et al, 2000). The simulation F100-INT is similar except that 100% of the soluble/internally mixed aerosols in clouds are assumed to be cloud-borne, and 0% of the insoluble aerosol is scavenged into the cloud droplets or crystals.…”

“…Prescribed aerosol scavenging fractions have traditionally been implemented in many GCMs, including ECHAM5-HAM, and some models have simply assumed that 100% of the aerosol in a cloud is scavenged into the cloud droplets and ice crystals (e.g., Barth et al, 2000;Chin et al, 2000;Takemura et al, 2002;Stier et al, 2005;Tie et al, 2005). This approach is desirable for the low computational expense.…”

Inter-Relationships and Seasonal Variations of Inorganic Components of Pm10 in a Western Pacific Coastal City

“…It has generally been found that SO 4 or NH 4 show fairly constant concentrations over wide areas (Pakkanen et al, 2001). Following Adams et al (1999), the source of particulate ammonium is from the condensation of gaseous ammonia, whilst those of particulate SO 4 are from condensation of gaseous sulfuric acid, and SO 2 to sulfate conversion (Barth et al, 2000). The major source (>73%) of SO 2 in Hong Kong is from power generation in the western part of the Territory ( CH2M Hill, 2002).…”

Modelling the reversible uptake of chemical species in the gas phase by ice particles formed in a convective cloud

“…Mari et al, 2000;Barth et al, 2000). The equilibrium between the gas phase and the liquid phase is given by the effective Henry's constant (Sander, 1999) and is not reached for all species on each model time step.…”