Summary of the cloud chemistry modeling intercomparison: Photochemical box model simulation

Abstract

[1] We report results of a cloud chemistry numerical modeling intercomparison, which shows good agreement among gas-aqueous photochemistry box models that are being used in the community. For the case studied, cloud chemistry depleted concentrations of CH 2 O, CH 3 OOH, HNO 3 , and O 3 , while H 2 O 2 (in the absence of sulfur chemistry), NO, and NO 2 increased. Because parcels of air usually flow in and out of cloud in a matter of minutes rather than remain in cloud for an hour, an optional simulation was performed in which frequent brief cloud encounters were represented. Representing a cloud intermittently rather than continuously does not alter the total concentration of many of the species. However CH 2 O and HCOOH concentrations are decreased and increased, respectively, because of the timing of the CH 2 O production during clear-sky intervals and its destruction during cloudy intervals. Further differences between a continuous cloud simulation and an intermittent cloud simulation are expected if pH is allowed to vary during the cloud periods. Simulating an intermittent cloud brought out the importance of using a chemistry time step that is a multiple of the cloud time step because deviations of results from a simulation in which the chemistry time step did not coincide with the appearance and disappearance of cloud were quite large. To better quantify the effect of cloud on HO x photochemistry, future investigations should include nonmethane hydrocarbon and sulfur chemistry. Future cloud chemistry modeling intercomparisons should bring in cloud physical and chemical measurements so that the models can be evaluated with observations.

Modelling study of the impact of deep convection on the utls air composition - Part I: Analysis of ozone precursors

“…As for CO, the ethane vertical distribution in the troposphere depends mainly on transport, photochemistry being negligible in the simulation. Boissard et al (1996) reached a similar conclusion from the analysis of the TROPOZ II measurements over eastern Brazil. The ethane 2-D distributions from Boissard at al.…”

“…This allows taking into account the scavenging of the most soluble species such as HNO 3 and H 2 O 2 . The pH in the liquid cloud phase is set to 4.93, as computed by two different cloud chemistry models in Barth et al (2003). A sensitivity simulation showed that the results are not significantly changed if a less acid pH value is used.…”

Distribution of hydrogen peroxide and formaldehyde over Central Europe during the HOOVER project

“…However, although recent convective influence can be ruled out, the peroxide ratio drops below unity, which would indicate "recently convectively influenced" airmasses according to the data filtering method described above. The measurements discussed above from the UTOPIHAN and HOOVER campaigns provide strong evidence that deep convective systems at the midlatitudes can transport both, highly soluble H 2 O 2 and less soluble CH 3 OOH effectively to the upper troposphere, in agreement with some publications (Snider et al, 1992;Barth et al, 2001bBarth et al, , 2003Salzmann et al, 2007). In a study by Kim et al (2002), as pointed out earlier, it is shown that cloud processing of airmasses may have different effects on the mixing ratios of H 2 O 2 depending on the general chemical conditions, including NO x concentrations and the time of day.…”

Implementation and evaluation of online gas-phase chemistry within a regional climate model (RegCM-CHEM4)

“…A suite of numerical procedures with efficient solutions has been developed (e.g., Jacobson et al, 1996), and here we apply the computationally rapid radical balance method (RBM) of Sillman et al (1991) and Barth et al (2002) to solve the tendency equation for photochemical production and loss. RBM utilizes the fact that much of the complexity of tropospheric chemistry stems from the HOx radical family (OH, HO 2 and RO 2 ), which has a limited set of of sources and sinks.…”