Abstract

The concentrations of atmospheric pollutants measured by the Dutch National Air Quality Monitoring Network (NAQMN) in 2011 do not differ greatly from those of preceding years. This is partly due to the absence in recent years of any extreme weather conditions that can affect air quality. However, during the first few months of 2011, there was an increase in particulate matter concentrations, especially during dry spells in the spring of 2011.
Measurements 2011
Up to June 11, 2011, the Netherlands had exemption from the European Union for complying with European particulate matter standards related to both the annual average concentration (40 micrograms per cubic meter) and the maximum number of days (35) with a maximum daily average of particulate matter concentration above 50 micrograms per cubic meter. During this period (early 2011) less stringent limit values were applicable. After this period the original limit values were reinstated.

In this annual overview, in view of the long-term objectives, both the less stringent and the original European limit values were applied to the measured particulate matter concentrations. The annual average concentration of particulate matter meets both these standards. The European limit value for the maximum number of days exceeding the less stringent daily limit was not exceeded. However, when the original daily limit was applied several exceedances at the NAQMN locations were found, something that has not occurred since 2007.

There is also a less stringent European limit value for nitrogen dioxide that is valid up to January 1, 2015. This level was not exceeded at any of the NAQMN locations. Similar to other years, exceedance of the EU standard for the annual average of nitrogen dioxide occurred at some traffic-related monitoring sites. Traffic contributes significantly to nitrogen dioxide concentrations. No exceedances were observed at rural and urban background stations.

There is also a less stringent European limit value for nitrogen dioxide that is valid up to January 1, 2015. This level was not exceeded at any of the NAQMN locations. Similar to other years, exceedance of the EU standard for the annual average of nitrogen dioxide occurred at some traffic-related monitoring sites. Traffic contributes significantly to nitrogen dioxide concentrations. No exceedances were observed at rural and urban background stations.

Trend analysis up to 2015
A trend analysis of the combined data set for particulate matter and nitrogen dioxide levels shows a decrease in concentrations over the long term, despite the slight increase in annual particulate matter levels for 2011. However, even if the decreasing trend in nitrogen dioxide concentrations continues at the same rate, compliance with the limit value at all monitoring sites by 2015 is uncertain. To guarantee such compliance requires a much stronger reduction than shown so far.

Renewal
During the past twenty years, the concentration levels of carbon monoxide and sulphur dioxide have decreased greatly. The monitoring obligations for these substances have subsequently been reduced and the NAQMN measurement strategy for these substances was adjusted in 2011. In addition, all ozone monitors were replaced in 2011. The old ozone monitors were found to underestimate ozone levels by about seven percent, therefore, a correction to the historical ozone data set was applied in 2011.