Cloud-scale model intercomparison of chemical constituent transport in deep convection

Transport and scavenging of chemical constituents in deep convection is important to understanding the composition of the troposphere and therefore chemistry-climate and air quality issues. High resolution cloud chemistry models have been shown to represent convective processing of trace gases quite well. To improve the representation of sub-grid convective transport and wet deposition in large-scale models, general characteristics, such as species mass flux, from the high resolution cloud chemistry models can be used. However, it is important to understand how these models behave when simulating the same storm. The intercomparison described here examines transport of six species. CO and O₃, which are primarily transported, show good agreement among models and compare well with observations. Models that included lightning production of NOx reasonably predict NOx mixing ratios in the anvil compared with observations, but the NOx variability is much larger than that seen for CO and O₃. Predicted anvil mixing ratios of the soluble species, HNO₃, H₂O₂, and CH₂O, exhibit significant differences among models, attributed to different schemes in these models of cloud processing including the role of the ice phase, the impact of cloud-modified photolysis rates on the chemistry, and the representation of the species chemical reactivity. The lack of measurements of these species in the convective outflow region does not allow us to evaluate the model results with observations.