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Three-dimensional model simulations and scientific results

- The new QUILT validated time series of ground-based data have been compared with SLIMCAT 3D CTM results. The model output acts as a transfer standard and shows large differences in column NO2 measured at nearby stations - probably indicating tropospheric pollution at one site.

At high latitudes the model overestimates column NO2 due to strong transport in the ECMWF analyses. The BrO comparisons are consistent with a current stratospheric loading of around 21pptv, although the model does not reproduce the sub tropical observations well. There is an inconsistency in the OClO comparisons: The model captures the magintude of the Arctic observations but overestimates the Antarctic ones.

- 3D model runs have been performed to look at the observed long-term trend in groundbased NO2 at sites such as Lauder, NZ. Over the period 1990-2003 the basic model does produce a trend similar in magnitude to the observations of around 8%/decade over this time. The observed trend is clearly larger than the observed trend of 3%/decade in the NOy source gas, N2O. There is a large contribution of decreasing aerosol loading during this period.

However, the model agreement with the observed trend is also due to a 'dynamical' trend in the model NOy column (i.e. a trend which is present even in a run with constant NOy) and related to a change in the altitude of the NOy profile (e.g. change in tropopause height).

More information on the QUILT project can be found at:

Reported by

School of Earth & Environement, University of Leeds
Woodhouse Lane
LS2 9JT Leeds
United Kingdom
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