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Berlin Environmental Atlas

03.06 Near Ground Ozone (Edition 1996)

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Maps 03.06.4, 03.06.5, 03.06.6 and 03.06.7: Results of the FluMOB-Measuring Campaign
in Berlin and Brandenburg from 23 July to 27 July 1994

The most frequent exceeding of the threshold values for ozone and the discussion arising from it, whether and in what manner the regional measures to reduce the ozone precursor substances can contribute was the reason for a measuring project jointly financed by the states of Berlin and Brandenburg. Along with the states commissioning the study, a further seven research institutes from Berlin, Brandenburg, Bavaria and Switzerland participated.

From 23 to 27 July 1994, two motor gliders measured the morning and afternoon ozone, nitrogen oxide and hydrocarbon concentrations (VOC) at altitudes between 300 and 3,000 m both within the city and the outlying regions.

These measurements were also taken at the broadcast tower in Frohnau and at 3 Air Quality Measuring vehicles. These were positioned in addition to the fixed ground stations of the Berlin and Brandenburg Monitoring Network in order to measure the pollution load in front of and behind the city. By means of an additional vertical measurement at several locations, the air currents and other meteorological phenomena were recorded (c.f. Stark et al. 1995).

Weather conditions and wide area ozone load

The measuring campaign of 23 to 27 July 1994 took place at the beginning of a long high summer period in which Berlin experienced an unprecedented series of 11 "hot days" with maximum temperatures of over 30 °C. The wide area air pressure distribution was characterized by a low pressure zone from the eastern Atlantic and high pressure zone from the Baltic Sea, southern Scandinavia, and the Baltic states.

Exemplary for the Berlin region are the wind direction and speeds at the BLUME measuring station 314, Charlottenburg City Hall tower, shown in Map 03.06.7 (Correlations of Different Parameters from 23 July to 27 July 1994). In comparison with these measuring points 60 m above ground, the measurements for the wind velocity at the Grunewald station (10 m above the stands) have been given.

From 23 to 25 July, an east to southeasterly air current with low humidity prevailed in Berlin and until noon on the 25 July a very continental air mass too. On the morning of 26 July, the wind turned toward the Northwest, combined with the injection of more humid, intensely subtropical air mass with a high dust concentration.

In order to assess this episode's contribution to transregional transport, a reverse trajectory was calculated from a three-dimensionally analyzed field of meteorological measurements (c.f. Reimer and Scherer 1991). In the Map 03.06.4 (Ozone Concentration from 23 July to 27 July 1994 at 4:00 p.m. CET) sind die are the reverse trajectories with travel time data until arrival in Berlin on each afternoon on four different days of the campaign are presented. According to the trajectory of 24 July, which closely resembled that of 23 July, the air originated until 25 July from the Baltic sea region and central and northern Poland, a region with relatively low emissions of ozone precursor substances. Therefore it contained only a relatively low ozone load of between 120 bis 150 µg/m³.

Map 03.06.4 also shows the spatially interpolated ozone concentration each day at 4:00 p.m. CET on the five days of the measurement campaign. Thus the largest wide-area ozone distribution at the time of the daily maximum is presented. Until 25 July, only values under 180 µg/m³ were recorded in the Northeast.

On 26 July, the reverse trajectories come out of the Czech Republic, Austria, Saxony, and on 27 July, from Switzerland and southern Germany. If one determines the ozone concentration of the air mass under way 48 hours before, using the figure in Map 03.06.4, then one comes to an ozone level already at 180 to 200 µg/m³ at the beginning of each trip. Also the high level of solar radiation on the way to Berlin means a significantly increased initial load of a similar magnitude to the second phase of the campaign could be expected.

This conforms with the development of ozone and NO2 concentrations at the Frohnau broadcast tower documented in Map 03.06.7. Especially during the last two measuring days, a 40 µg/m³ higher ozone level and even higher nitrogen oxide levels could be observed at the tower whose measurement series represents more the transregional pollution influences because it lay windward to Berlin.

Results of the Airborne Measurements

In the course of the measuring campaign between 23 - 27 July, an average of one morning and one afternoon flight per day was undertaken by each aircraft.

The horizontal distribution of the minute average for the ozone concentration on the flight path at about 500 m altitude has been shown using the example in Map 03.06.5 (Spatial Distribution of Ozone Concentration) for the afternoon of 25 July.

The circle's diameter is the measure for the recorded concentration in ppb (comprises somewhat less than 2 µg/m³) interpolated between the smallest and largest level measured. Map 03.06.6 (Spatial Distribution of NO2 Concentration) yields the same picture for the nitrogen dioxide levels.

Leeward to the main wind direction, there is a significant rise in the ozone concentration. This area lay northeast of the city on 25 July (and the previous days), while on 27 July, the areas south of Berlin were effected by the ozone increase due to the change in the wind to NW-N. This is the explanation for the heavy increase in the ozone values at the Müggelsee station on the 26th and 27th July as can be seen in Map 03.06.7. On these days, the maximum values exceeded the windward levels of over 50 µg/m³ recorded at the broadcast tower in Frohnau.

In both maps, the airborne measurements depicted show a good correspondence between the ozone and NO2 maximum and the spatial extension of Berlin as emission source for ozone-forming substances. The measured NO2 concentrations serve as an excellent index- the windward levels were only 2 - 4 ppb, while the peak concentration in the air layer above the city lay at over 20 ppb. As Map 03.06.6 shows, the leeward side of the city exhibited increased NO2 levels even as far as 30 - 40 km from the city.

In contrast to the source proximate areas, where maximums for nitrogen oxide concentrations, as a result of their ozone-decomposing effect, correspond to the ozone minimums (c.f. Map 03.06.3), shows a simultaneous increase in both types at the outgoing air vane. The highest ozone levels appeared leeward. In comparison to the windward levels, they were usually combined with higher NO2 concentrations. This applies also to the majority of the recorded hydrocarbon compounds and indicates a significantly increased ozone formation potential leeward.

A comparison of the leeward and windward ozone levels measured on all afternoon flights is shown in Figure 9. From 23 - 25 July, the lee effect decreased due to the mixing layer and the higher wind velocity on 24 July. It was much less on both of the last days on which an increase in the ozone concentration up to 44 % of the windward level occurred.

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Fig. 9: Ozone Concentration During the Airborne Measurements at approx. 500 m Altitude from 23 to 27 July 1994, Afternoons

Table 2 shows a compilation of the near ground ozone concentration windward and leeward levels measured in the afternoon in the Berlin municipal area. Just as in the aircraft data measured afternoons, there is a continuous increase in the windward prior pollution load on the outskirts amounting to approximately 20 µg/m³ per day. On 26 and 27 July, it exceeds the information value of 180 µg/m³ prescribed by the EC Guidelines. Within the urban residential areas of Berlin, a slightly lower level prevails due to the ozone destruction by freshly emitted nitrogen oxides.

The proportional growth in ozone pollution leeward lay at the same level as had been calculated by the aircraft measurements and was the lowest on 25 July. It increased significantly on the days following, 26 and 27 July.

Maps 03.06.8 and 03.06.9: Results of the Photochemical Simulation Calculation

In Map 03.06.8 8 (Calculated Near Ground Ozone Concentration), a simulation of the ozone distribution in Berlin and greater parts of Brandenburg using the photochemical dispersion model REGOZON is shown for 25 July 1994, 4:00 p.m. CET (c.f. Mieth and Unger 1993). All available meteorological data and emission information about as many relevant pollutants as possible was taken from the Berlin and Brandenburg emission cadastre to try to generate a computer model of the complicated chemical and meteorological processes. This has the advantage, providing that the simulation is sufficiently correspondent with reality, that different emission scenarios can be simulated under exactly the same conditions to test their effects on ozone reduction.

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Tab. 2: Level of Measured Near Ground Ozone Concentration from 23 to 27 July 1994 given in µg/m³

Excel
[Table is also available as Excel-File (MS-Excel is required).]

As Map 03.06.8 shows, the highest afternoon ozone values in Brandenburg have been calculated for Northwest of Berlin. In Berlin only the northwestern boroughs of Spandau, Heiligensee and Frohnau are effected by increased ozone concentrations. In contrast, areas with significantly higher emissions (esp. the city center) exhibit significantly lower ozone levels during the entire simulation. Altogether, the 25 July also shows a visible ozone producing potential caused by emissions in the area under investigation. The calculated background concentrations lie between 160 and 180 µg/m³. The position of the calculated ozone vane as well as the calculated levels in the vane in the afternoon coincide well with observations. The breadth of the vane is somewhat underestimated (c.f. Map 03.06.5 with 03.06.8).

Scenarios

The emission reduction for the scenario calculation was oriented on measures and effect prognoses which, according to then current planning, could have been implemented for acute measures in the context of a summer smog ordinance.

The reductions which could have been obtained for the various polluter groups are shown in Table 3.

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Tab. 3: Emission Reductions for Individual Polluter Groups in Percent

Excel
[Table is also available as Excel-File (MS-Excel is required).]

The effect of an emissions reduction by approx. 30 %, as difference between the calculated concentrations in the scenario and real case, is shown in Map 03.06.9 (Difference in the OX Concentration OX = O3 + NO2). The result is a significant decrease in ozone load in the conurbation’s outgoing air vane of up to 15 µg/m³, resp. of about 7 %. In the Berlin city center, the ozone concentration increases a little bit above the background load level. Since the city center is subject to heavy NO emissions from motor vehicle traffic, which in turn reacts with the ozone to form NO2, the ozone concentration drops relative to the background load in the reference run. Nonetheless, the sum of oxidants OX (OX = O3 + NO2) generally increases. To assess the effect of the measures, the difference between the OX concentrations in the scenario and reference run are shown in Map 03.06.9. This makes it possible to recognize an improvement in the air by means of a reduced oxidant load in the especially polluted Berlin city center.

The same simulation of conditions on the last day of the campaign (27 July 94) yields a somewhat greater reduction in the ozone maximums by 10 % in the leeward area of the city. If one calculated the size of the area with the concentrations above 180 µg/m³ ozone for reference and scenario cases, then there is a quite respectable reduction of 60 % on 25 July. Since there was a high pollution level of nearly 180 µg/m³ on 27 July (c.f. Fig. 9 and Tab. 2) which could not have been effected by the measures in the region, the reduction in the area with ozone levels exceeding 180 µg/m³ was only marginal.

Measures to Protect the Stratospheric Ozone Layer and to Reduction of the Near Ground Ozone Load

High near ground concentrations are a great wide-area problem in central Europe. The measurements and simulations from the FluMOB project and similar activities in other federal state (c.f. LAI 1996) show that high ozone peaks have been reached on a few days of the year leeward of the larger conurbations. These lie between 15 and 40 % above the wide-area ozone load. Temporary regional measures during an ozone alarm can help to reduce the regional extra production if a drop in the emissions of ozone precursor substances (nitrogen oxide and hydrocarbons) has reached at least 20 %. However, the area in a larger conurbation subject to such measures must include all the areas of neighboring conurbations in order to take into account regional transport. This makes the approach realized in the Ozone Law (§ 40a BImSchG) really sensible: namely, to declare ozone alarm normally for a larger region. An ozone reduction, which should avoid exceeding the EC-wide valid threshold values, requires nonetheless a combination of wide-area and regional measures which include at least a one third reduction in the emission of ozone precursor substances. This requires a concept which agreed at national and European levels.

To prevent the thinning out of the ozone layer in the stratosphere globally or to limit it, reduction of the CFC emissions and the decrease in air traffic in the stratosphere must be striven for as fast as possible. A first attempt, as part of the Montreal conference of 1987, proved unsuitable because of its excessively long time limits for ending emissions and its abundant exceptions. At the follow-up conferences in 1990 and 1992 in London and Copenhagen, a production stop could be agreed for most CFC compounds by the turn of the millennium. Within the European framework, this has already taken place. Until 2015, there are exceptions for partially-halogenated substances which have a reduced ozone-destroying potential. It is decisive for the global reduction of chlorine and bromine emissions that the developing and newly industrialized countries can be convinced to quickly discontinue their not insignificant CFC and halon production capacity and that they receive the financial aid and support for the production of substitutes.

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