Interannual variability of tropospheric composition: the influence of changes in emissions, meteorology and clouds 1Centre for Atmospheric Science, University of Cambridge, UK
2Met Office, Exeter, UK
3Lancaster Environment Centre, Lancaster University, UK
*now at: NASA Goddard Institute for Space Studies & Columbia University, Center for Climate Systems Research, New York, USA
**now at: NOAA Earth System Research Laboratory, Boulder, Colorado, USA
Received: 15 June 2009 – Published in Atmos. Chem. Phys. Discuss.: 26 June 2009 Abstract. We have run a chemistry transport model (CTM) to systematically examine
the drivers of interannual variability of tropospheric composition during 1996–2000.
This period was characterised by anomalous meteorological conditions
associated with the strong El Niño of 1997–1998 and intense wildfires, which produced a large amount of
pollution. On a global scale, changing meteorology (winds, temperatures,
humidity and clouds) is found to be the most important factor
driving interannual variability of NO2 and ozone on the timescales considered.
Changes in stratosphere-troposphere exchange, which are largely driven by
meteorological variability, are found to play a particularly important
role in driving ozone changes. The strong influence of emissions on NO2
and ozone interannual variability is largely confined to areas where intense biomass burning
events occur. For CO, interannual variability is almost solely driven by
emission changes, while for OH meteorology dominates, with the radiative
influence of clouds being a very strong contributor. Through a simple
attribution analysis for 1996–2000 we conclude that changing cloudiness
drives 25% of the interannual variability of OH over Europe by
affecting shortwave radiation. Over Indonesia this figure is as high as 71%.
Changes in cloudiness contribute a small but non-negligible amount (up to 6%) to the interannual
variability of ozone over Europe and Indonesia. This suggests that future
assessments of trends in tropospheric oxidizing capacity should account for interannual variability
in cloudiness, a factor neglected in many previous studies.
Revised: 24 February 2010 – Accepted: 26 February 2010 – Published: 11 March 2010
Citation: Voulgarakis, A., Savage, N. H., Wild, O., Braesicke, P., Young, P. J., Carver, G. D., and Pyle, J. A.: Interannual variability of tropospheric composition: the influence of changes in emissions, meteorology and clouds, Atmos. Chem. Phys., 10, 2491-2506, doi:10.5194/acp-10-2491-2010, 2010.