Impact of climate change on tropospheric ozone and its global budgets G. Zeng, J. A. Pyle, and P. J. Young National Centre for Atmospheric Science, Department of Chemistry, University of Cambridge, Cambridge, UK
Abstract. We present the chemistry-climate model UMCAM in which a relatively detailed
tropospheric chemical module has been incorporated into the UK Met Office's
Unified Model version 4.5. We obtain good agreements between the modelled
ozone/nitrogen species and a range of observations including surface ozone
measurements, ozone sonde data, and some aircraft campaigns.
Four 2100 calculations assess model responses to projected changes of
anthropogenic emissions (SRES A2), climate change (due to doubling CO2), and
idealised climate change-associated changes in biogenic emissions (i.e. 50% increase
of isoprene emission and doubling emissions of soil-NOx). The global
tropospheric ozone burden increases significantly for all the 2100 A2
simulations, with the largest response caused by the increase of anthropogenic
emissions. Climate change has diverse impacts on O3 and its budgets through
changes in circulation and meteorological variables. Increased water vapour
causes a substantial ozone reduction especially in the tropical lower
troposphere (>10 ppbv reduction over the tropical ocean). On the other hand,
an enhanced stratosphere-troposphere exchange of ozone, which increases by
80% due to doubling CO2, contributes to ozone increases in the
extratropical free troposphere which subsequently propagate to the surface.
Projected higher temperatures favour ozone chemical production and PAN
decomposition which lead to high surface ozone levels in certain regions.
transports ozone precursors more rapidly out of the boundary layer resulting
in an increase of ozone production in the free troposphere. Lightning-produced
NOx increases by about 22% in the doubled CO2 climate and contributes
to ozone production.
The response to the increase of isoprene emissions shows that
the change of ozone is largely determined by background NOx levels: high
NOx environment increases ozone production; isoprene emitting regions with
low NOx levels see local ozone decreases, and increase of ozone levels in
the remote region due to the influence of PAN chemistry. The calculated ozone
changes in response to a 50% increase of isoprene emissions are in the range
of between −8 ppbv to 6 ppbv. Doubling soil-NOx emissions will increase
tropospheric ozone considerably, with up to 5 ppbv in source regions.
Citation: Zeng, G., Pyle, J. A., and Young, P. J.: Impact of climate change on tropospheric ozone and its global budgets, Atmos. Chem. Phys., 8, 369-387, doi:10.5194/acp-8-369-2008, 2008.