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.

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

Nitrous oxide (N2O) is an important greenhouse gas and the major source of stratospheric reactive nitrogen (NOy), an active participant in the stratospheric chemistry controlling ozone depletion. Tropospheric N2O abundances are increasing at nearly 0.3% yr-1 and this increase is expected to continue in the near future as are direct stratospheric NOy perturbations, for example, from aircraft. In order to test and gain confidence in three-dimensional (3-D) model simulations of the stratospheric N2O-NOy system, a simplified photochemistry for N2O and NOy is developed for use in chemistry transport models (CTMs). This chemical model allows for extensive CTM simulations focusing on uncertainties in chemistry and transport. We compare 3-D model simulations with measurements and evaluate the effect on N2O and NOy of potential errors in model transport, in column and local ozone, and in stratospheric temperatures. For example, with the three different 3-D wind fields used here, modeled N2O lifetimes vary from 173 to 115 years, and the unrealistically long lifetimes produce clear errors in equatorial N2O profiles. The impact of Antarctic denitrification and an in situ atmospheric N2O source are also evaluated. The modeled N2O and NOy distributions are obviously sensitive to model transport, particularly the strength of tropical upwelling in the stratosphere. Midlatitude, lower-stratospheric NOy/N2O correlations, including seasonal amplitudes, are well reproduced by the standard model when denitrification is included. These correlations are sensitive to changes in stratospheric chemistry but relatively insensitive to model transport. The lower stratospheric NOy/N2O correlation slope gives the correct net NOy production of about 0.5 Tg N yr-1 (i.e., the cross-tropopause flux as in the Plumb-Ko relation) only when N2O values from 250 to 310 ppb are used. As a consequence, the Synoz calibration of the flux of O3 from the stratosphere to the troposphere needs to be corrected to 550 ± 140 Tg O3 yr-1. Copyright 2001 by the American Geophysical Union.

From the ensemble of stations that monitor surface air quality over the United States and Europe, we identify extreme ozone pollution events and find that they occur predominantly in clustered, multiday episodes with spatial extents of more than 1000 km. Such scales are amenable to forecasting with current global atmospheric chemistry models. We develop an objective mapping algorithm that uses the heterogeneous observations of the individual surface sites to calculate surface ozone averaged over 1° by 1° grid cells, matching the resolution of a global model. Air quality extreme (AQX) events are identified locally as statistical extremes of the ozone climatology and not as air quality exceedances. With the University of California, Irvine chemistry-transport model (UCI CTM) we find there is skill in hindcasting these extreme episodes, and thus identify a new diagnostic using global chemistry-climate models (CCMs) to identify changes in the characteristics of extreme pollution episodes in a warming climate. © 2014 Author(s).