Methyl bromide( CH3Br)s uppliesa bouth alf of the chemicallya ctiveb romine (Bry)in thes tratospheEreff.o rtsto c ontroBl ry-catalyzoezdo ned epletiobny p hasinogu t, for example,a griculturaul seo f CH3Brm ay be thwartedb y a lack of understandinogf how the variedb iogeochemicapl rocesseisn teracta s a coupleds ystem: in additiont o the chemical industry,l argen aturals ourcesc omef rom the ocean;a ndl osseso ccuri n the atmosphereo, cean,a nd soils. A simplifiedo ne-dimensionaslt ratosphere-troposphere-ocean modeflo r (CH3BrB, ry• thatf itsc urrenut nderstandoinfg s ourceasn ds inksis a nalyzeidn termso f naturalm odes. Surfacea nd oceans ourcesh ave effectively different steadys tate lifetimes (1.0 and0 .5 years,r espectively)b, ut the natural-moded ecayt imeso f the system (1.8y earsfo rC H3Bra nd4 .5y earsfo rs tratospheBrircy )d on otd epenodn t hel ocationo f sources.T he cumulativeo zoned epletionr esultingf rom a singlea tmosphericre leaseo f CH3Brin tegrateosv ert hec onsequesnlto wr isea ndf all of Bryi n thel owers tratosphere. Thus, in spiteo f the 1-yearl ifetime of CH3Br,o nly half of the anticipatedo zoner ecovery occurs in the first 7 years.

Nitrous oxide (N2O) is one of the top three greenhouse gases whose emissions may be brought under control through the Framework Convention on Climate Change. Current understanding of its global budget, including the balance of natural and anthropogenic sources, is largely based on the atmospheric losses calculated with chemical models. A representative one-dimensional model used here describes the photochemical coupling between N2O and stratospheric ozone (O3), which can easily be decomposed into its natural modes. The primary, longest lived mode describes most of the atmospheric perturbation due to anthropogenic N2O sources, and this pattern may be observable. The photolytic link between O3 and N2O is identified as the mechanism causing this mode to decay 10 to 15 percent more rapidly than the N2O mean atmospheric lifetime, affecting the inference of anthropogenic sources.

Estimates of continental sources of CFC-11, CFC-12, CCl , CH CCl and N O are derived from the atmospheric lifetime experiment in Adrigole, Ireland, and anthropogenic emissions of CCl and N O from Europe have been identified. Relative source strengths are consistent with global budgets for the halocarbons and N O. Different industrial release patterns for halocarbons are observed for Europe, the western United States and Australia. © 1985 Nature Publishing Group. 4 3 3 2 4 2 2

THE direct reaction of HOC1 with HC1, known to occur in liquid water and on glass surfaces , has now been measured on surfaces similar to polar stratospheric clouds and is shown here to play a critical part in polar ozone loss. Two keys to understanding the chemistry of the Antarctic ozone hole are, one, the recognition that reactions on polar stratospheric clouds transform HC1 into more reactive species denoted by ClO (refs 812) and, two, the discovery of the ClO-dimer (C1 O ) mechanism that rapidly catalyses destruction of O (refs 1315). Observations of high levels of OClO and ClO in the springtime Antarctic stratosphere confirm that most of the available chlorine is in the form of ClO (refs 20, 21). But current photochemical models have difficulty converting HC1 to ClO rapidly enough in early spring to account fully for the observations . Here I show, using a chemical model, that the direct reaction of HOC1 with HC1 provides the missing mechanism. As alternative sources of nitrogen-containing oxidants, such as N O and ClONO , have been converted in the late autumn to inactive HNO by known reactions on the sulphate-layer aerosols , the reaction of HOC1 with HC1 on polar stratospheric clouds becomes the most important pathway for releasing that stratospheric chlorine which goes into polar night as HC1. © 1992 Nature Publishing Group. 1 2 3,4 5-7 1619 5-7,20,21 24-27 x 2 2 3 x 22,23 x 2 5 2 3

Atmospheric CH perturbations, caused directly by CH emissions or indirectly by those of CO are enhanced by chemical feedbacks. They can be diagnosed in terms of the natural modes of atmospheric chemistry that are general solutions of the continuity equations. Each mode is a pattern in the global distribution of all chemical species, and each has a single time-constant that accurately describes its exponential decay about a given atmospheric state. This mathematical theory extends earlier work and is general for 2-D and 3-D chemistry-transport models. A formal proof relates the steady-state distribution and its lifetime to the integral of the true time-dependent response (properly included in the recent IPCC assessment). Changes in CO are also known to perturb CH ; however, the impact of CO emissions on climate has not been formally assessed in part because the short lifetime of CO (months) relative to that of CH (decade) was believed to limit the integrated impact. Using the IPCC model studies, this theory predicts that adding 5 CO molecules to today's atmosphere is equivalent to adding 1 CH molecule with the same decadal duration as direct CH addition. Extrapolating these results, CH sources would have to triple before runaway growth, wherein CH emissions exceed the oxidizing capacity of the troposphere. Copyright 1996 by the American Geophysical Union. 4 4 4 4 4 4 4 4

A new approach for modeling photolysis rates (J values) in atmospheres with fractional cloud cover has been developed and is implemented as Cloud-J - a multi-scattering eight-stream radiative transfer model for solar radiation based on Fast-J. Using observations of the vertical correlation of cloud layers, Cloud-J 7.3c provides a practical and accurate method for modeling atmospheric chemistry. The combination of the new maximum-correlated cloud groups with the integration over all cloud combinations by four quadrature atmospheres produces mean J values in an atmospheric column with root mean square (rms) errors of 4 % or less compared with 10-20 % errors using simpler approximations. Cloud-J is practical for chemistry-climate models, requiring only an average of 2.8 Fast-J calls per atmosphere vs. hundreds of calls with the correlated cloud groups, or 1 call with the simplest cloud approximations. Another improvement in modeling J values, the treatment of volatile organic compounds with pressure-dependent cross sections, is also incorporated into Cloud-J.