ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-11-25605-2011 Impact of the isoprene photochemical cascade on tropical ozone Paulot F. 1 Henze D. K. 2 Wennberg P. O. 1 3 Division of Engineering and Applied Sciences, California Institute of Technology, Pasadena, California, USA Department of Mechanical Engineering, University of Colorado, Boulder, Colorado, USA Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA 13 09 2011 11 9 25605 25654 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys-discuss.net/11/25605/2011/acpd-11-25605-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/11/25605/2011/acpd-11-25605-2011.pdf

Tropical tropospheric ozone affects Earth's radiative forcing and the oxidative capacity of the atmosphere. Considerable work has been devoted to the study of the processes controlling its budget. Yet, large discrepancies between simulated and observed tropical tropospheric ozone remain. Here, we characterize some of the mechanisms by which the photochemistry of isoprene impacts the budget of tropical ozone. At the regional scale, we find that isoprene nitrates can account for up to 70% of the local NO<sub>x</sub> sink. Using forward sensitivity simulations, we show that the modulation of O<sub>x</sub> by isoprene nitrates photochemistry can be characterized by their net impact on NO<sub>x</sub>. We use adjoint sensitivity simulations to demonstrate that the oxidation of isoprene can affect ozone outside of continental regions through the transport of NO<sub>x</sub> over near-shore regions (e.g., South Atlantic) and the oxidation of isoprene outside of the boundary layer far from its emissions regions. The latter mechanism is promoted by the simulated low boundary-layer oxidative conditions. In our simulation, ~20% of the isoprene is oxidized above the boundary layer in the tropics. Changes in the interplay between regional and global effect are discussed in light of the forecasted increase in anthropogenic emissions in tropical regions.

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