Joyce Penner and Sanford Sillman, University of Michigan

Research Objectives

To evaluate the role of emissions of volatile organic carbon species (VOCs) and other energy-related pollutants from biomass and fossil fuel burning on the chemical climatology of the global troposphere, with an emphasis on the role of these pollutants in altering O3 photochemistry and the chemistry of CH₄, both of which are important greenhouse gases.

Computational Approach

We have developed a global tropospheric chemical model that is capable of treating the chemistry of CO, CH₄, NO_x, and a suite of VOCs. The model is computationally fast, while providing much better chemical resolution than is available in other tropospheric chemistry models, and is configured so that it may also be run interactively with a climate model.

In order to study the sources of CO and CH₄ in the model, we have simplified the chemistry of the troposphere to mainly focus on the interactions between OH, CH₄, and CO. Ambient distributions of 17 species were calculated for a prescribed methane and CO distribution using the 3D chemistry-transport model GRANTOUR. Meteorology was provided for a 4.5° × 7.5° resolution every 12 hours over a yearly cycle. This simulation was used to diagnose reaction rate coefficients as a function of latitude, longitude, height, and time.

Accomplishments

Comparison of the predicted CO and CH₄ concentrations with data from the NOAA Climate Monitoring and Diagnostics Laboratory indicated that our initial sources result in an underestimate of CO concentrations. Therefore, we adjusted the fossil fuel sources up by a factor of 1.7. The new sources result in a much improved comparison of predicted and observed CO concentrations. We are continuing to use the model to help refine our understanding of CO sources. In addition, we are building a version of the model with interactive isoprene chemistry. This will allow us to determine the additional effects of non-methane hydrocarbon chemistry on the concentration of OH.

Significance

Our model represents a significant advance over previous models for tropospheric chemistry because it includes a full suite of VOCs with explicit chemistry represented in the model. These simulations should improve our estimates of the effects of fossil fuel and biomass burning on the global climate by better quantifying the source magnitude and distribution of both biomass and fossil fuel burning. A better definition of the source strength of CO from fossil fuels and from biomass burning will also help us to quantify the sources of aerosols (sulfates and smoke). In contrast to the greenhouse gases, aerosols tend to cool the climate. Thus, the quantification of these sources is extremely important.

Annual average surface concentrations of CO (in ppbv) from fossil fuel sources (top) and biomass burning sources (bottom).

Publications

J. E. Penner, C. C. Chuang, and K. Grant, "Climate forcing by carbonaceous and sulfate aerosols," Climate Dynamics 14, 839 (1998).

J. E. Penner, D. Bergmann, J. J. Walton, D. Kinnison, M. J. Prather, D. Rotman, C. Price, K. E. Pickering, and S. L. Baughcum, "An evaluation of upper tropospheric NO_x with two models," J. Geophys. Res. Atmos. 103, 97 (1998).

U. Lohmann, J. Feichter, J. E. Penner, and R. Leaitch, "Indirect effect of sulfate and carbonaceous aerosols: A mechanistic treatment," J. Geophys. Res. Atmos. (submitted).

http://aoss.engin.umich.edu/Penner/