Abstract. This paper presents a review of the main ozone destroying catalytic cycles operating in the stratosphere. Particular attention is paid to the kinetic aspects of these cycles such as the rate limiting step and chain length. Although it is an important kinetic parameter, the chain length of the various cycles is seldom considered when the various catalytic cycles are discussed. This survey highlights that in the low stratosphere the cycles involving HO: and halogens (notably bromine) are particularly important. In approximate order of effectiveness the most important ozone loss cycles in the polar lower stratosphere are the BrO/C10, HO2/BrO, and OH/HO2 cycles.

For the first time, the method of four-dimensional variational data assimilation is applied to the analysis of chemically active trace species. By combining observations with a numerical model to analyse siniultaneously several species over a period of a few days, the analysis method is able to exploit information which is not available to conventional analysis techniques. Moreover, effective use can be made of asynoptic observations even for species which have strong diurnal cycles. Synoptic analyses are produced. A Lagrangian approach is adopted, allowing a separation of dynamics and chemistry which considerably reduces the computational expense of the method.A stratosphere-troposphere data assimilation system. Mom Weather Rev., 122,686702 Variational assimilation of meteorological observations with the adjoint of the vorticity equations. Part I. Theory. Q.

Abstract. With the exception of acetone it is not generally recognized how important atmospheric carbonyls and alkyl radicals are in the lower stratosphere and upper troposphere. Carbonyl compounds are the crucial intermediate species for the autocatalytic production of OH. For example, in the upper troposphere and lower stratosphere it is calculated based on data assimilation analysis of Atmospheric Trace Molecule Spectroscopy Experiment (ATMOS) data that CH3 production due to the degradation of carbonyls contributes around 40% to the overall production of CH3, a key initiation step for HOx production, with the contribution due to the photolysis of CH3CHO being comparable to that of acetone. So correctly modeling the alkyl radical concentrations is of central importance and has not be given the attention it deserves to date. The reactions of carbonyls with Br and C1 are also major sources of HBr and HC1. In short, carbonyl compounds play a central role in atmospheric chemistry close to the tropopause, and this is directly relevant to issues such as the assessment of the impact of air traffic, and ozone depletion.

A three‐dimensional (3D) radiative‐dynamical‐chemical model has been developed and used to study the evolution of trace gases in the Arctic lower stratosphere during winter 1989–1990. A series of 10‐day model integrations were performed throughout this period. The model includes a comprehensive scheme of gas phase chemical reactions as well as a parameterization of heterogeneous reactions occurring on polar stratospheric cloud (PSC) surfaces. An important element of a 3D chemical model is the transport scheme. In this study the transport of chemical species is achieved by a non diffusive method well suited to the preservation of sharp gradients. During the winter studied temperatures were cold enough for the formation of both type I and type II polar stratospheric clouds from early December to early February. Model simulations in late December show that inside the polar vortex air is rapidly processed by polar stratospheric clouds converting HCl and ClONO2 to active chlorine. The possibility of ozone destruction depends strongly on the amount of sunlight. In early February an average ozone loss of 15 ppbv (parts per billion by volume) /day is predicted in PSC‐processed air at 50 hPa, giving a column loss of just under 1 DU/day. This loss increases to 25 ppbv/day if PSCs persist until March with a column loss of around 1.5 DU/day. The relatively small magnitude of the ozone loss predicted in the model, compared to the variability of ozone induced by dynamics, highlights the problems in identifying the signature of chemical ozone loss in the Arctic. In future years significant ozone depletion could occur if PSCs persist until late March. The efficiency of the catalytic cycles responsible for the ozone loss has been analyzed as a function of latitude, altitude and time. In general, the cycle involving ClO + ClO is the dominant loss mechanism in the polar lower stratosphere. Cycles involving BrO can make a relatively large contribution early in the season and when the levels of ClO are low. The cycle initiated by ClO + O destroys ozone at altitudes above 30 hPa but the loss is compensated, to some extent, by in situ ozone production. The results for trace species are validated, where possible, by comparison with the available measurements, although the sparse nature of the observations does not effectively constrain the model.

Abstract. This paper considers the nature of carbonaceous surfaces, the means by which they are activated, the nature of some functional groups that they support, and some reaction mechanisms that may be involved. Because of the strong affinity of carbonaceous surfaces for organic species and because of the ease with which compounds in a high oxidation state can oxidize the carbonaceous surface, it is highly likely that carbonaceous aerosols are interacting chemically with a range of organic species in ways that have, as yet, not been fully characterized but may significantly affect the oxidizing capacity of our atmosphere. If HONO is formed on the surface of carbonaceous aerosols then this could be a significant source of HOz as HONO is readily photolyzed to give OH, and it could explain the large values of HONO often observed in the troposphere. In general, the reduction of NO• on carbonaceous aerosols is an important consideration, and it is addressed here.