An extended ozone episode occured in August. Maximum ozone concentration of the year 1997 have been measured at many sites in North Rhine-Westphalia (NRW) ( own analysis with data of the Landesumweltamt).
This episode was investigated in the framwork of Forschungsverbund Verkehr und Umwelt. It was intended to show the applicability of the model system CARLOS. CARLOS (Chemistry And dispersion in a Regional und LOcal Scale) is a joint development in the framework of the FVU with the model EURAD-CTM2 and FOOT3DK/WiTraK, which are used in the special research area SFB419 at the University of Cologne.
Sensitivity studies with the EURAD-CTM were carried out to illustrate transport and chemical impact of emission, which are generated in North Rhine-Westphalia.
|
|
| Figure 1: Computed ozone concentrations in ppb at approximatly 0 to 40 m height at 14 UTC or 16 Uhr MESZ, 13. August 1997. A band of higher ozone concentration is located over North Rhine-Westphalia which runs from Swiss to the North Sea. At the next day this structure will be moved to the east. |
Simulations with computed emissions and the meteorology of the investigated episode were made in a first step to calculate the base case. Emission sources, which are located in NRW, were neglected in a second simulation. Biogenic emissions were treated in the same way as in the base case. This case will be termed zerocase (zero anthropogenic emissions in NRW)
Because the investigated time interval (7. August 1997 - 14. August 1997) is a part of an episode with high ozone concentrations, the potential of reduction at high ozone concentrations can be seen by looking at the results. The reduction in this case would result through the unlikely action of reducing all emissions to zero. Another interpretation would be, that all emittors within NRW, would work with perfect waste gas cleaning, while other countries in Germany use standard techniques. In the figure, plotting the differences between both cases, the "dispersion of impact" in form of areas of higher or minor concentration of polluted air is shown. The major wind direction changed from West to East and South, which is clearly shown by transport mechanismen in the animations (see Results).
Results:
Base case 3.5 MByte MPEG-Movie. Click here to start animation. The simulation starts at 7. August 1997. The first two days (7., 8. August) serve as spin-up time for the model: beginning from initial values described in the literature (especially background concentration of ozone etc.) an atmospheric condition is reached, which describes a realistic distribution of atmospheric pollutants. The simulated episode (9. - 14. August) shows a slow accumulation of ozone, which peaks at 13. August (Figure 1) . The weather situation changes in the night of 13./14. August and the concentrations in NRW decrease noticeably. The area with high ozone concentrations moved to the East (Figure 2).
 |
| Figure 2: Calculated ozone concentration in ppb at approximatly 0 to 40 m height at 14 UTC or 16 MESZ, 14. August 1997. The band of high ozone concentration located over North Rhine-Westphalia day before moved to the East. |
Difference of zerocase - base case 1.6 MByte MPEG-Movie. Click here to start animation. The visualization clearly shows the extension of the ozone plume, which was generated in NRW. This ozone plume is given as the difference of the two cases. Relative changes are illustrated in % (Zero - Base)/Base. Concentrations of the zerocase minus those of the base case results in positive changes, if the deactivation of emission sources leads to higher ozone concentrations. This is represented during night time in areas with NOx emissions. In this area, NOx leads to a decrease of ozone during night time. Negative changes show, that reduced ozone concentrations were calculated in the zero case.
Difference zero case - base case 1.7 MByte MPEG-Movie. Click here to start animation. Relative changes of NO concentratons are plotted in this animation. An area with clearly minor NO concentration, spreading quickly over NRW, is shown. Although emissions are decreasing, there are some areas with increasing NO. The reason for that is a change in ozone concentration: At sites, where less ozone can react with NO (because the level of ozon decreased), higher NO levels remain.
Acknowledgment
This work was funded from Ministerium
für Wissenschaft und Forschung, Nordrhein-Westfalen. Part of emission
data and data of the TEMES network were provided from the Landesumweltamt
Essen. Support of the Bildungsministerium
für Wissenschaft und Forschung is a base of our work in EURAD, as well
as the financial support of the Rheinische Institut für Umweltforschung
(RIU), Cologne. Data for the meteorological model were prepared with support
of Prof. P. Speth, Dr. I. Stiefelhagen and Dr. Birdie Roeben, University
of Cologne. Dr. H. Jakobs (RIU) calculated wind fields with MM5, Dr. M.
Memmesheimer (RIU) created the emission database. Computing time was provided
from Forschungszentrum Jülich, especially ZAM,
ICG2
and ICG3.
To look at the animation (MPEG format), click at the links (Base, Difference) .
