Brendan D. Field

Global budget of methanol: Constraints from atmospheric observations

factor of 3 higher for young than from mature leaves. The atmospheric lifetime of methanol in the model is 7 days; gas-phase oxidation by OH accounts for 63% of the global sink, dry deposition to land 26%, wet deposition 6%, uptake by the ocean 5%, and aqueous-phase oxidation in clouds less than 1%. The resulting simulation of atmospheric concentrations is generally unbiased in the Northern Hemisphere and reproduces the observed correlations of methanol with acetone, HCN, and CO in Asian outflow. Accounting for decreasing emission from leaves as they age is necessary to reproduce the observed seasonal variation of methanol concentrations at northern midlatitudes. The main model discrepancy is over the South Pacific, where simulated concentrations are a factor of 2 too low. Atmospheric production from the CH3O2 self-reaction is the dominant model source in this region. A factor of 2 increase in this source (to 50–100 Tg yr � 1 ) would largely correct the discrepancy and appears consistent with independent constraints on CH3O2 concentrations. Our resulting best estimate of the global source of methanol is 240 Tg yr � 1 . More observations of methanol concentrations and fluxes are needed over tropical continents. Better knowledge is needed of CH3O2 concentrations in the remote troposphere and of the underlying organic chemistry.

A Tropospheric Ozone Maximum Over the Middle East

The GEOS-CHEM global 3-D model of tropo- spheric chemistry predicts a summertime O3 maximum over the Middle East, with mean mixing ratios in the middle and upper troposphere in excess of 80 ppbv. This model feature is consistent with the few observations from commercial air- craft in the region. Its origin in the model reflects a complex interplay of dynamical and chemical factors, and of anthro- pogenic and natural influences. The anticyclonic circulation in the middle and upper troposphere over the Middle East funnels northern midlatitude pollution transported in the westerly subtropical jet as well as lightning outflow from the Indian monsoon and pollution from eastern Asia transported in an easterly tropical jet. Large-scale subsidence over the region takes place with continued net production of O3 and little mid-level outflow. Transport from the stratosphere does not contribute significantly to the Oa maximum. Sensi- tivity simulations with anthropogenic or lightning emissions shut off indicate decreases of 20-30% and 10-15% respec- tively in the tropospheric O3 column over the Middle East. More observations in this region are needed to confirm the presence of the O3 maximum.

Oxygenated volatile organic chemicals in the oceans: Inferences and implications based on atmospheric observations and air-sea exchange models

(10 � 9 mol L � 1 ) and 2 nM and net fluxes of 1.1 � 10 � 12 g cm � 2 s � 1 and 0.4 � 10 � 12 gc m � 2 s � 1 are calculated for acetaldehyde and propanal, respectively. Large surface seawater concentrations are also estimated for methanol (100 nM) and acetone (10 nM) corresponding to an undersaturation of 6% and 14%, and a deposition velocity of 0.08 cm s � 1 and 0.10 cm s � 1 , respectively. These data imply a large oceanic source for acetaldehyde and propanal, and a modest sink for methanol and acetone. Assuming a 50–100 meter mixed layer, an extremely large oceanic reservoir of OVOC, exceeding the atmospheric reservoir by an order of magnitude, can be inferred to be present. Available seawater data are both preliminary and extremely limited but indicate rather low bulk OVOC concentrations and provide no support for the existence of a large oceanic reservoir. We speculate on the causes and implications of these findings. INDEX TERMS: 0312 Atmospheric Composition and Structure: Air/sea constituent fluxes (3339, 4504); 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry. Citation: Singh, H. B., A. Tabazadeh, M. J. Evans, B. D. Field, D. J. Jacob, G. Sachse, J. H. Crawford, R. Shetter, and W. H. Brune, Oxygenated volatile organic chemicals in the oceans: Inferences and implications based on atmospheric observations and air-sea exchange models, Geophys. Res. Lett., 30(16), 1862, doi:10.1029/ 2003GL017933, 2003.

Imaging Geostationary Fourier Transform Spectrometer-revolutionary tool for tropospheric chemistry

The Geostationary Imaging Fourier Transform Spectrometer (GIFTS) has been selected by the National Aeronautics and Space Administration (NASA) for its 2004 New Millennium Program mission. The GIFTS geophysical data products are derived from measurements of atmospheric thermal emission in 2 spectral bands: 685-1130 cm/sup -1/ and 1650-2250 cm/sup -1/, at high spectral resolution (up to 0.3 cm/sup -1/) on a 4-km spatial grid. Among key data products are vertically-resolved distributions of ozone and carbon monoxide. Vertical resolution attainable is in the range of 3- to 11-km, depending on a target gas and altitude. To evaluate the GIFTS capability for atmospheric chemistry studies, e.g., sources, sinks, transport and transformation of trace gas, simulations of the GIFTS observations have been performed. Real aircraft in situ profiles and results of the Harvard 3-D model were used as inputs for the simulations.