Aarhus Universitets segl

No. 37: The Danish Air Quality Monitoring Programme. Annual Summary for 2011

Ellermann, T., Nøjgaard, J.K., Nordstrøm, C., Brandt, J., Christensen, J., Ketzel, M. & Jensen, S. S. 2012. The Danish Air Quality Monitoring Programme. Annual Summary for 2011. Aarhus University, DCE – Danish Centre for Environment and Energy, 63 pp. Scientific Report from DCE – Danish Centre for Environment and Energy. http://www2.dmu.dk/Pub/SR37.pdf

Summary and Conclusion

This report presents the result from the Danish Air Quality Monitoring Programme in 2011. The monitoring programme is carried out by the DCE - Danish Centre for Environment and Energy (DCE) at Aarhus University. The core part of this programme consists of continuous measurements at nine monitoring stations; seven stations situated in the four largest cities and two stations located in background areas. These measurements are supplemented with model calculations using DCE’s air quality models.

The aim of the program is to monitor air pollutants relevant to human health in accordance with the EU air quality directives. The programme includes measurements of sulphur dioxide (SO2), nitrogen oxides (NOx/NO2), particulate mass (PM10 and PM2.5), particle number, benzene (C6H6), toluene (C7H8), carbon monoxide (CO), ozone (O3), lead (Pb), arsenic (As), cadmium (Cd), mercury (Hg), nickel (Ni), and polycyclic aromatic hydrocarbons (PAH). In 2009 the programme was expanded with measurements of a number of volatile organic compounds (VOC’s) that are precursors for formation of ozone. The measurements and model calculations are used to evaluate the Danish air quality in relation to limit values as well as to follow trends. Further, the program serves as basis for determination of sources of the air pollutants, basis for evaluation of the impact of regulations of emissions and as basis for various research projects related to air quality.

In 2011 there have been the following major changes in the monitoring programme compared to 2010:

  • Activities concerning measurements of heavy metals were reduced in 2010 because a new analysis technique (ICP-MS) was used for analysis of heavy metals. In 2011 and 2012 this analysis technique has been improved and DCE are now able to analyse for more than 20 heavy metals in the particle samples compared to only four compounds in 2010. This report presents results from measurements of 10 selected heavy metals in 2011.
  • This year presents results of daily sodium concentrations for the street stations. These measurements are carried out in order to be able to determine the contribution from salting of roads and sea salt. These results has been used to evaluate the impact of salt on the exceedance of the daily limit value for PM10.
  • Finally, the report presents results from measurements of the chemical composition the main constituents of PM2.5 at H.C. Andersens Boulevard (Copenhagen/1103) and Risø. 

PM10 were at all the stations below both the annual limit value (40 µg/m3). The daily limit value for PM10 (50 µg/m3 must not be exceeded more than 35 days annually) were exceeded at both street stations in Copenhagen, while no exceedances were observed in the two other cities where PM10 are measured (Aarhus and Odense). The two exceedances in Copenhagen fall under article 20 and 21 of the Air Quality Directive as they can be attributed to natural sources (sea salt) and winter-salting. Section 7.4 of this report contains information on the deductions made primarily based on measurements of sodium.

PM2.5 was lower than the annual limit value (25 µg/m3) valid from 2015. The number of particles in ambient air was about 14000 particles per cm3 at the street station H.C. Andersens Boulevard. This is considerably higher than in urban and rural background. A significant reduction in particle number has been observed since 2002.

The sodium content in PM10 on street stations were about 1.5 µg/m3 corresponding to an estimated annual salt content (NaCl) of about 4.0 µg/m3. High diurnal values of salt were observed during periods with winter salting of roads.

The annual limit value for NO2 (40 µg/m3 in 2011) was exceeded at one street station in Copenhagen (H.C. Andersens Boulevard), whereas no exceedances were observed in Odense, Aalborg and Aarhus. The NO2 concentrations decreased from 2010 to 2011 at part of the stations while no changes was observed at the remaining part. At H.C Andersens Boulevard (Copenhagen/1103) there were still elevated concentrations of NO2. These are believed to be a temporary effect due to local construction work at nearby sites to the measurement station that causes increased emissions from non-road machinery used for the construction work and from re-directed and/or congested traffic. These are under further investigation.

Model calculations at selected streets in Copenhagen and Aalborg indicate that the limit value was exceeded at several streets in Copenhagen but not at any streets in Aalborg in 2011. In general, modelling confirmed that the street station at H.C. Andersens Boulevard (1103) in Copenhagen represents one of the most polluted streets in Copenhagen, whereas the traffic station in Aalborg (6153) represents a site with a pollution load at the average level for the 31 selected streets in Aalborg.

The ozone levels were in 2011 almost the same as in 2010 at all rural and urban background stations and no clear trend was thus observed. The information threshold at 180 µg/m3 was not exceeded in 2011. The target value for the max 8 hours ozone concentration on 120 µg/m3 was not exceeded, but the long-term objective for this target was exceeded at all non-traffic stations.

The report presents results for volatile organic compounds (VOC) measured at the urban background in Copenhagen. VOC’s can act as ozone precursors, although the formation of ozone in Denmark is in general small due to moderate solar radiation. The ozone pollution in Denmark is to a large extent the result of long distance transport of pollutants from other European countries south of Denmark.

The levels of SO2 and heavy metals have decreased for more than two decades and are now far below the limit values. The limit values for benzene and CO are not exceeded and the levels have decreased for the last decade.

Measurements of particle bound PAH concentrations were performed at H.C. Andersens Boulevard, Copenhagen. The average concentration of benzo[a]pyrene was 0.21 ng/m3. The target value for benzo[a] pyrene (1 ng/m3) was not exceeded in 2011.

For the first time this report presents results from determination of the chemical content in PM2.5. The annual average concentrations of NH4+, Na+, K+, Mg2+, Cl-, NO3-, SO42- are very similar at the street station at H.C. Andersens Boulevard and at the rural station at Risø. The main differense between the two stations are for elemental carbon (EC), organic matter (OM) and Ca2+ where the concentrations are higher at the street station compared to the rural background station. This is mainly due to emissions of these compounds from the traffic in Copenhagen.

Actual data, annual and multi-annual summaries are available at the website