Vol. 22, No. 5
Quality in Denmark
Environmental Research Institute, Department of Atmospheric Environment
Denmark is situated in Northern Europe in a generally cool, windy,
and moist coastal climate. Air pollution levels are usually moderate
compared with Southern and Eastern Europe, which have higher emission
densities and more intense photochemical activity. However, the environmental
impact of air pollution still gives rise to concern, principally because
of health effects owing to human exposure to fine and ultrafine particles.
Other issues include nitrogen deposition that contributes to eutrophication
of coastal waters, damage to sensitive terrestrial ecosystems owing
to atmospheric deposition of nutrients and acidifying compounds, and
Air quality monitoring is carried out within the Danish Urban Air Quality
Monitoring Program  and the Nationwide Danish Monitoring
Program  for air quality in the rural areas. Data
from these programs can be accessed from the following web site: www.dmu.dk/AtmosphericEnvironment/netw.htm.
Current guidelines are not exceeded in Danish cities, and future European
Union (EU) guidelines are expected to be met as well .
Measurements are supplemented with model calculations, and recently
this effort has been extended with an operational Danish air pollution
forecasting system, THOR , from which results are
also accessible on the Internet.
The Danish urban monitoring program was established in 1982, and it
currently comprises a network with stations in three cities (a fourth
city will soon be included). Monitoring is carried out through cooperation
among the Danish Environmental Protection Agency, the National Environmental
Research Institute (NERI), the Greater Copenhagen Air Monitoring Unit,
and the municipal authorities in the cities of Odense and Aalborg. NERI
is responsible for operating the program together with the Agency of
Environmental Protection of Copenhagen, the Environmental and Food Control
Agency of Funen, and the Department for the Environment and Urban Affairs
of Aalborg. Data are published in quarterly reports in Danish and are
summarized in annual reports in English . Data are
also available on the Internet.
Various actions have had a pronounced positive effect on urban air
quality in Danish cities. Lead pollution has been reduced by a factor
of about 50 since 1982 as a result of the removal of lead from gasoline.
A reduction of benzene content in gasoline from approximately 3.5%
in 1994 to around 1% in 1998, together with the introduction of Three-Way
Catalytic (TWC) converters, led to a substantial reduction in ambient
benzene concentrations, as revealed in a recently concluded personal
exposure study on benzene . The introduction of
TWC has, in general, reduced emissions of hydrocarbons, nitrogen oxides,
and carbon monoxide from individual passenger cars considerably (typically
Based on actual kilometers traveled, the percentage of gasoline cars
having TWC is estimated to be about 67%. This reduction is evident in
the observed trends in nitrogen monoxide (NO) from the monitoring stations
(Fig. 1), whereas the trend for the more harmful nitrogen dioxide (NO2)
is much less pronounced. In vehicle exhaust, NO usually accounts for
about 90 to 95% of the nitrogen oxide (NO + NO2) emissions,
but NO2 is formed in a rapid reaction between NO and ozone
in ambient air, usually with ozone as the limiting factor for NO2
formation in streets. Ambient ozone is mainly a result of long-range
transport from Central and Eastern Europe, and local emission reduction
strategies have, therefore, had only limited effect on NO2
concentrations in streets in Danish cities. Impact studies of the new
EU vehicle emission standards show that air quality in Danish cities
will improve further .
1 Concentrations of nitrogen oxides at Danish Urban Air Quality
stations from 1982 to 1999. (Larger view Top,
Concentrations of total suspended particulate (TSP) matter have also
decreased, partly as a result of reduced sulfur emissions. There are
indications, however, that health effects may be related to fine and
ultrafine particles rather than to particle mass. Various research activities
have, therefore, been initiated to explore the characteristics (size,
distributions, chemical compositions, etc.) of particle pollution in
urban areas, and thereby to provide the tools for determining the most
efficient reduction strategies [6,7].
The Nationwide Danish Background Monitoring Program was established
in 1989, and results are reported annually [2,8].
The program assembles information on nutrient input to the Danish aquatic
and forest ecosystems. Turnovers are frequently observed in Danish coastal
waters and lead in worst-case situations to the death of fish and benthic
fauna. Air quality and precipitation measurements are currently performed
at eight locations selected to represent coastal and island-based areas,
as well as inland areas. At all sites, bulk collectors capture precipitation
over semimonthly periods. The samples are analyzed for their content
of nutrients and metal ions. Furthermore, six stations are equipped
with filter pack samplers to collect compounds in the gas and particle
In the later years, a decrease in atmospheric nitrogen concentrations
is evident from the observations (Fig. 2). A similar tendency has been
observed for wet depositions, although the decrease is less pronounced,
owing to dependency on the precipitation amount. Atmospheric nitrogen
deposition to coastal waters, however, contributes significantly to
the overall loads. For inner Danish waters, estimates have shown that
the atmosphere contributes about 30 to 40% of the total nitrogen loads.
The measurements in Danish monitoring programs are supplemented by
model calculations. In the urban monitoring program, calculations with
the carefully validated Operational Street Pollution Model (OSPM) 
allow for estimates of concentration levels in streets without monitoring,
and make it possible to evaluate the effects of various actions toward
reduction of pollution from urban traffic. In the background monitoring
program, the Atmospheric Chemistry and Deposition (ACDEP) 
model is used to study the geographical distribution of nitrogen deposition
to Danish marine waters, and to evaluate sourcereceptor relationships.
Data from THOR  have recently been released on the
Internet. THOR is an integrated modeling system based on weather forecasts
from the ETA model , on air pollution forecasts
derived from a long-range transport pollution model known as the Danish
Eulerian Operational Model (DEOM), on the Urban Background Pollution
Model (UBM), and on the Operational Street Pollution Model (OSPM).
1. K. Kemp and F. Palmgren. The Danish
Air Quality Monitoring Program. Annual Report for 1998. NERI, Tech.
Rep. No. 296, 64 p. (1999).
2. H. Skov, O. Hertel, T. Ellermann,
C. Ambelas Skjøth, N. Z. Heidam. NOVA 2003, Atmospheric Deposition
of Nitrogen (in Danish). NERI, Tech. Rep. No. 289, 102 p. (1999).
3. S. S. Jensen, R. Berkowicz, M. Winther,
F. Palmgren, Z. Zlatev. Future Air Quality in Danish Cities. Impact
Study of the New EU Vehicle Emission Standards, Technical Report available
at www.mst.dk (2000).
4. J. Brandt, J. H. Christensen, L.
M. Frohn, R. Berkowicz, F. Palmgren. The DMU-ATMI THOR Air Pollution
Forecast SystemSystem Description, NERI, Tech. Rep. No. 321, 60
p. (2000) available at www.dmu.dk.
5. H. Skov, A. B. Hansen, G. Lorenzen,
H. V. Andersen, P. Løfstrøm, C. S. Christensen. Benzene
Exposure of People Living and Working in Copenhagen. Submitted to Atmospher.
6. F. Palmgren, P. Wåhlin, R.
Berkowicz, R. van Dingenen. Fine Particles from Traffic. EUROTRAC Symposium
2000. March 2531, 2000. Garmisch-Partenkirchen, Germany. To appear
7. P. Wåhlin, F. Palmgren, R.
van Dingenen. Experimental Studies of Ultrafine Particles in Streets
and the Relationship to Traffic. To appear in Atmospher. Environ. (2000).
8. M. F. Hovmand, L. Grundahl, O. H.
Manscher, A. Egeløv, H. V. Andersen. Atmospheric Deposition on
Danish Forests, Data Report 1992/93 (in Danish), NERI, Tech. Rep. No.
122, 63 p. (1994).
9. R. Berkowicz, O. Hertel, N. N. Sørensen,
J. A. Michelsen. In Modeling Air Pollution from Traffic in Urban Areas.
Flow and Dispersion Through Obstacles, R .J. Perkins and S. E. Belcher
(Eds.). Clarendon Press, Oxford, 121142, (1997).
10. O. Hertel, J. Christensen, E.
H. Runge, W. A. H. Asman, R. Berkowicz, M. F. Hovmand, Ø. Hov.
Atmospher. Environ. 29, 11, 12671290 (1995).
11. S. Nickovic, D. Mihailovic, B.
Rajkovic, A. Papadopoulos. The Weather Forecasting System SKIRON, Vol.
II. Description of the Model, University of Athens Report, 228 p. (1998).
This article is one in a series
by IUPACs Commission on Atmospheric Chemistry (VI.2) about air
quality in IUPAC member countries [Project
620/12/89]. It was contributed by Ole Hertel (E-mail: [email protected];
Tel.: +45 4630 1148; Fax: +45 4630 1214; Web site: http://www.dmu.dk/AtmosphericEnvironment/netw.htm),
Finn Palmgren, Thomas Ellermann, Henrik Skov, Kåre Kemp, Mads
F. Hovmand, and Jørgen Brandt of the National Environmental Research
Institute, Department of Atmospheric Environment, P.O. Box 358, Frederiksborgvej
399, 4000 Roskilde, Denmark.