Likelihood of meeting the EU limit values for NO2 and PM10 concentrations in the Netherlands

In 2007, the European limit values for annual average nitrogen dioxide (NO2) concentration and for daily average particulate matter (PM10) concentration were exceeded along motorways and city streets in the Netherlands. While the road length along which the exceedance occurred is uncertain, model calculations show that the NO2 concentration was likely to have been exceeded (chance >66%) along about 300 km and PM10 concentration along about 75 km. In addition, the limit values were exceeded ‘about as likely as not’ (chance 33–66%) along a total of 1000 km for NO2 and 1600 km for PM10. PM10 and NO2 concentrations must be below the limit values everywhere in Europe, ultimately by 2011 and 2015, respectively. Since estimates of future local concentrations have an uncertainty of about 15–20%, no absolute statements can be made whether concentrations will be below the limit values within the specified time. Model calculations accounting for the effects of current and proposed national and European legislation, and using average meteorology for large-scale and local traffic contributions show strong decreases in likely limit value exceedances in the Netherlands. However, limit value exceedances are still possible (chance >33%) along about 350 km for PM10 by 2011, and about 150 km for NO2, by 2015. These possible exceedances depend not only on the uncertainties and on national and European policies and their effectiveness, but also on contributions by specific additional local measures. The Netherlands Government has proposed a plan, which includes local measures to meet the limit values everywhere, in time. Although not assessed here due to their specific character, such local measures could reduce exceedances. As the effects of local measures and estimates of concentrations are uncertain, continuous monitoring – possibly together with additional measures – will be needed to adhere to the limit values.