Atmos. Chem. Phys. Discuss., 12, 9247-9281, 2012
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Evaluation of two isoprene emission models for use in a long-range air pollution model
A. Zare1,2, J. Brandt2, J. H. Christensen2, and P. Irannejad1
1Institute of Geophysics, University of Tehran, Iran
2Department of Environmental Science, Aarhus University, Denmark

Abstract. Knowledge about isoprene emissions and concentration distribution is important for chemistry transport models (CTMs), because isoprene acts as a precursor for tropospheric ozone and subsequently affects the atmospheric concentrations of many other atmospheric compounds. Isoprene has a short lifetime, and hence it is very difficult to evaluate its emission estimates against measurements. For this reason, we coupled two isoprene emission models with the Danish Eulerian Hemispheric Model (DEHM), and evaluated the simulated background ozone concentrations based on different models for isoprene emissions. In this research, results of using the two global biogenic emission models; GEIA (Global Emissions Inventory Activity) and MEGAN (the global Model of Emissions of Gases and Aerosols from Nature) are compared and evaluated. The total annual emissions of isoprene for the year 2006 estimated by using MEGAN is 732 Tg yr−1 for an extended area of the Northern Hemisphere, which is 50% higher than that estimated by using GEIA. The overall feature of the emissions from the two models are quite similar, but significant differences are found mainly in Africa's savannah and the rain forests of South America, and in some subtropical regions, such as the Middle East, India and the southern part of North America. Differences in spatial distribution of emission factors are found to be a key source of these discrepancies. In spite of the short life-time of isoprene, a direct evaluation of isoprene concentrations using the two biogenic emission models has been made against available measurements in Europe. Results show that the two models in general represent the measurements well and that the CTM is able to simulate isoprene concentrations. Additionally, investigation of ozone concentrations resulting from the two biogenic emission models show that isoprene simulated by MEGAN strongly affects the ozone production in the African savannah; the effect is up to 20% more than that obtained using GEIA. In contrast, the impact of using GEIA is higher in the Amazon region with more than 15% higher ozone concentrations compared to that of using MEGAN. Comparing the results for ozone concentrations for Europe obtained by using the two different models with measurements, show that the MEGAN emission model improves the model performance significantly in the Mediterranean area.

Citation: Zare, A., Brandt, J., Christensen, J. H., and Irannejad, P.: Evaluation of two isoprene emission models for use in a long-range air pollution model, Atmos. Chem. Phys. Discuss., 12, 9247-9281, doi:10.5194/acpd-12-9247-2012, 2012.
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