Sensitivities in global scale modeling of isoprene R. von Kuhlmann1, M. G. Lawrence1, U. Pöschl2, and P. J. Crutzen1,3 1Max-Planck-Institut für Chemie, Postfach 3060, 55020 Mainz, Germany 2Institut für Wasserchemie, Technische Universität München, München, Germany 3Scripps Institution of Oceanography, UC San Diego, La Jolla, CA, USA
Abstract. A sensitivity study of the treatment of isoprene and related parameters in 3D
atmospheric models was conducted using the global model of tropospheric chemistry
MATCH-MPIC. A total of twelve sensitivity scenarios which can be grouped into four thematic categories were
performed. These four categories consist of simulations with different chemical
mechanisms, different assumptions concerning the deposition characteristics of
intermediate products, assumptions concerning the nitrates from the oxidation
of isoprene and variations of the source strengths. The largest differences in ozone compared to the reference
simulation occured when a different isoprene oxidation scheme was used (up to
30-60% or about 10 nmol/mol). The largest differences in the abundance of peroxyacetylnitrate (PAN) were found when the isoprene emission strength was
reduced by 50% and in tests with increased or decreased efficiency of the deposition of intermediates. The deposition assumptions were also found to
have a significant effect on the upper tropospheric HOx production.
Different implicit assumptions about the loss of intermediate products were identified as a major reason for the deviations among the tested
isoprene oxidation schemes. The total tropospheric burden of O3
calculated in the sensitivity runs is increased compared to the background methane chemistry by
26±9 Tg( O3) from 273 to an average from the sensitivity runs of
299 Tg(O3). % revised Thus, there is a spread of ± 35% of the overall effect of isoprene in the model among the tested
scenarios. This range of uncertainty and the much larger local deviations found in the
test runs suggest that the treatment of isoprene in global models can only be
seen as a first order estimate at present, and points towards specific processes in need of focused future work.
Citation: von Kuhlmann, R., Lawrence, M. G., Pöschl, U., and Crutzen, P. J.: Sensitivities in global scale modeling of isoprene, Atmos. Chem. Phys., 4, 1-17, doi:10.5194/acp-4-1-2004, 2004.