Meteorological variability in NO2 and PM10 concentrations in the Netherlands and its relation with EU limit values

The extent of the exceedance of the EU limit values for nitrogen dioxide (NO2) and particulate matter (PM10) concentrations within the Netherlands is expected to decrease significantly, in the coming years. Whether limit values will actually be exceeded, in the next decade, depends not only on European, national and local policies, but also on the effects of inevitable interannual meteorological fluctuations. An analysis of model calculations and measurements yields variations (1 sigma) in the annual average concentration of about 5% for NO2 and 9% for PM10, due to meteorological fluctuations. These deviations from long-term average concentrations affect assessments of future levels, set against limit values. For instance, an NO2 concentration of 39 mu g m(-3), estimated for a given year with long-term average meteorology, indicates that it is likely (chance >66%) that the limit value of 40 mu g m(-3) will not be exceeded in that particular year. At the same time, the estimation also indicates, for example, that this situation is unlikely (change <33%) to continue for three years in a row. However, with an estimated concentration of 38 mu g m(-3), it is likely that the limit value will not be exceeded for three years in a row. The limit value for the daily average PM10 concentration is equivalent to an annual average of about 32 mu g m(-3). This threshold is unlikely to be exceeded for three years in a row, when an annual average concentration of 29 mu g m(-3) is estimated. Interannual variations in concentrations of NO2 and PM10 are linked to large-scale meteorological fluctuations. Therefore, similar results can be expected for other European countries. (C) 2009 Elsevier Ltd. All rights reserved.