A model for studies of tropospheric ozone and nonmethane hydrocarbons: Model description and ozone results

We have developed a global three-dimensional chemistry-meteorology model for studies of ozone and hydrocarbons in the troposphere, called Model of Atmospheric Transport and Chemistry-Max-Planck-Institute for Chemistry Version (MATCH-MPIC). The model currently calculates the distributions of 54 species and 141 reactions using a new flexible chemical integration method in connection with a fast general Rosenbrock solver. The reactions can be easily expanded for future studies with the model. The model includes updated emission inventories, an explicit dry deposition scheme, online photolysis rates, extensive budgeting capabilities and a correction for the so-called "mass-wind inconsistency'' problem. One-year simulations at two different horizontal resolutions, approximately 1.9degrees x 1.9degrees (T63) and 5.6degrees x 5.6degrees (T21), both with 28 vertical levels, are extensively evaluated with available observations from surface stations, ozonesondes, and field campaigns. The model is generally able to reproduce the observations of ozone to within 10 nmol/mol, but it overestimates upper tropospheric ozone at northern high-latitude stations in winter and spring and tends to underestimate the summer maximum in the free troposphere. In the tropics the chemical tropopause is sometimes too low. Generally, the low-resolution run yields only slightly worse agreement with observations compared to the higher-resolution run, thus making it suitable for further sensitivity studies. In a simulation using different meteorological data, O-3 agrees much better with observations in the upper troposphere, possibly because of the higher resolution near the tropopause. The net ozone production integrated over all tropospheric regions with a net production and loss separately reveals that the calculated chemically induced redistribution of ozone in the troposphere is 2-3 times larger than the net stratospheric influx. Even in the upper troposphere, photochemical production is of similar magnitude to the stratospheric influence.