Abstract. The Model for Ozone and Related chemical Tracers, version 4 (MOZART-4) is an offline global chemical transport model particularly suited for studies of the troposphere. The updates of the model from its previous version MOZART-2 are described, including an expansion of the chemical mechanism to include more detailed hydrocarbon chemistry and bulk aerosols. Online calculations of a number of processes, such as dry deposition, emissions of isoprene and monoterpenes and photolysis frequencies, are now included. Results from an eight-year simulation (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007) are presented and evaluated. The MOZART-4 source code and standard input files are available for download from the NCAR Community Data Portal (http://cdp.ucar.edu).

The microwave rotational spectra of malonaldehyde and a number of its isotopic forms have been investigated. In the vapor phase the molecule is found to exist in a planar, intramolecularly hydrogen-bonded form with two equivalent, individually asymmetric equilibrium configurations between which tunneling occurs. The data indicate that the hydrogen bond may be described by a double-minimum potential function. The large amplitude tunneling motion complicates structure determination,(1) (a)

Time and wavelength-resolved infrared fluorescence techniques are used to study the photofragmentation dynamics of CH2I2 and CH3I at the excimer laser wavelengths of 248 and 308 nm. Emission is detected from vibrationally excited CH2I and CH3 radicals as well as from the excited iodine atoms [I*(2P1/2→2P3/2)] produced in the photolysis. A complete infrared fluorescence spectrum of the highly excited CH2I radical is obtained as a function of time after the 248 nm dissociating laser pulse, providing both spectroscopic and vibrational deactivation data for the radical. Significant CH2I emission is observed at all wavelengths, indicating that excitation occurs into a very high density of states, nearing the vibrational quasicontinuum. Stronger emission features are observed in the region of the C–H stretching vibrations, the CH2 bending motion, and a combination band of these two modes. Deactivation rates for various spectral features of the highly excited CH2I radical with CH2I2 and argon are presented, along with a discussion concerning the relaxation of the highly excited radical spectrum. In the photolysis of CH3I at 248 nm, infrared fluorescence is observed directly from the out-of-plane bend of the CH3 radical. In addition, at 248 nm, the quantum yield (ΦI*) for I*(2P1/2) production is measured to be 0.81±0.03 for CH3I and 0.46±0.04 for CH2I2, while dissociation of CH2I2 at 308 nm yields ΦI*=0.25±0.02. The I* quenching rates with CH3I and CH2I2 are measured to be (2.5±0.4)10−13 and (3.6±0.3)10−13 cm3 molecule−1 sec−1, respectively.

The most extensive set of free tropospheric ozone measurements ever compiled across midlatitude North America was measured with daily ozonesondes, commercial aircraft and a lidar at 14 sites during July-August 2004. The model estimated stratospheric ozone was subtracted from all profiles, leaving a tropospheric residual ozone. On average the upper troposphere above midlatitude eastern North America contained 15 ppbv more tropospheric residual ozone than the more polluted layer between the surface and 2 km above sea level. Lowest ozone values in the upper troposphere were found above the two upwind sites in California. The upper troposphere above midlatitude eastern North America contained 16 ppbv more tropospheric residual ozone than the upper troposphere above three upwind sites, with the greatest enhancement above Houston, Texas, at 24 ppbv. Upper tropospheric CO measurements above east Texas show no statistically significant enhancement compared to west coast measurements, arguing against a strong influence from fresh surface anthropogenic emissions to the upper troposphere above Texas where the ozone enhancement is greatest. Vertical mixing of ozone from the boundary layer to the upper troposphere can only account for 2 ppbv of the 16 ppbv ozone enhancement above eastern North America; therefore the remaining 14 ppbv must be the result of in situ ozone production. The transport of NOx tracers from North American anthropogenic, biogenic, biomass burning, and lightning emissions was simulated for the upper troposphere of North America with a particle dispersion model. Additional box model calculations suggest the 24 ppbv ozone enhancement above Houston can be produced over a 10 day period from oxidation reactions of lightning NOx and background mixing ratios of CO and CH4. Overall, we estimate that 69–84% (11–13 ppbv) of the 16 ppbv ozone enhancement above eastern North America is due to in situ ozone production from lightning NOx with the remainder due to transport of ozone from the surface or in situ ozone production from other sources of NOx

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