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.

Abstract. 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.

Helium is removed at an average rate of 10(6) atoms per square centimeter per second from Venus's atmosphere by the solar wind following ionization above the plasmapause. The surface source of helium-4 on Venus is similar to that on Earth, suggesting comparable abundances of crustal uranium and thorium.

The distribution of 222Rn over North America is simulated with a 3-d chemical tracer model (CTM) based on the meteorology of the GISS general circulation model (GCM). Model results are compared to surface observations from 5 sites in the United States. It is found that the 222Rn concentrations are regulated primary by dry convection. At night, the model underpredicts observations because it does not resolve the sharp 222Rn concentration gradient which forms near the surface. In daytime, the predicted and observed concentrations are usually in good agreement. Inspection of seasonal trends reveals, however, several significant discrepancies which are traced to anomalies in the GCM meteorology. -from Authors