European scale exceedance mapping for PM10 and ozone based on daily interpolation fields ETC/ACC Technical Paper 2007/8

14 Mar 2008

Summary
In this report focus is given to the use of daily statistical data, i.e. creating maps on a daily basis, and combining these daily maps to derive the air quality indicators. The indicators assessed are a) the annual mean PM10 concentration, b) the number of days above the limit value of 50 µg/m-3 for PM10 and c) the number of days above the target value of 120 µgm-3 for the maximum daily 8 hour running mean for ozone.

A number of interpolation methods are tested and the use of a variety of supplementary datasets, including both the EMEP and the LOTOS-EUROS chemical transport models (CTM), is assessed. The results of the daily mapping methods are compared to those from the annual mapping in regard to the statistical performance of the methods as well as the methods available for determining uncertainty.

It is found that residual kriging after multiple linear regression is the best performing interpolation methodology for all indicators on both a daily and an annual basis. In addition, the use of daily mapping is generally found to perform better than the annual maps for the majority of years and indicators studied. Both of the CTMs applied give similar results but the LOTOS-EUROS model is found to perform best for PM10 with the EMEP model performs best for ozone.

It is recommended to use daily mapping methods when the number of exceedance days are to be mapped. If annual statistics are to be used for mapping daily exceedances then it is recommended to use the percentile value, i.e. the n’th highest daily concentration, as the indicator rather than the number of exceedance days.

When annual means are to be mapped both the assessment and uncertainty maps using the daily and annual methods give very similar results, though the daily mapping is slightly better. Mapping of these indicators can be carried out using the annual statistics only.

Prepared by: Bruce Denby1, Jan Horálek2, Peter de Smet3, Frank de Leeuw3, Pavel Kurfürst2

1Norwegian Institute for Air Research (NILU), Norway
2Czech Hydro Meteorological Institute (CHMI), Czech Republic
3Netherlands Environmental Assessment Agency (MNP), The Netherlands

Published by: ETC/ACC, January 2008, 53 pp.

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