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Berlin Environmental Atlas

03.06 Near Ground Ozone (Edition 1993)

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Map 03.06.2: Mean Day Course on Summer Days 1992

The map shows the medium day course of the ozone concentration at several stations of the Berlin Air Quality Monitoring Network.

The form of the day course curves at the three ground stations Heiligensee, Mitte and the freeway are to be explained in first approximation by the superimposition of the course of nitrogen oxide emissions through the motor vehicle traffic and the exchange conditions of the atmosphere. The ozone minimum is to be found between 5.00 and 7.00 o'clock in the morning hours. At this time the motor vehicle traffic is already quite heavy, the nightly ground inversion however still pronounced. Hence it is virtually impossible for the ozone-decomposing nitrogen oxides to move upward and/or the ozone-rich air from the top to move downward. The ozone decomposition on the outskirts of town is effective also, because on one hand the pollutants from the city are transported there also, e.g. to the most leeward Heiligensee measuring station. On the other hand a reaction of the ozone with the materials at the ground occurs in the nightly cold air layer also.

The conditions at 324 m elevation, recorded by the gauge at the radio tower in Frohnau, are completely different. There the ozone level remains at summer days on average above the MIK value of 120 µg/m³ (cf. VDI Guideline 2310), because this air layer is isolated at night by ozone-decomposing processes on the ground. This changes in the morning when the sun has warmed the blocking layer on the ground so far that the vertical air exchange starts. Then the tower measuring point is temporarily affected by the polluted air ascending from the ground, in which slighter ozone concentration is present. The minimum at the tower normally appears between 9.00 and 10.00 o'clock in the morning.

At this time the ozone concentration at the other stations has already risen noticeably because ozone from the superimposed storage layer is transported to the ground. The station Heiligensee and the tower measuring point display a roughly parallel course. The further thinning by the ozone-decomposing pollutants and the photochemical processes, urged on through the intense solar radiation, have caused the ozone concentration in the entire lower atmosphere to rise further.

Near nitrogen oxide sources, particularly at the city expressway and somewhat more weakly at the station Mitte, the ozone-decomposing effect of the freshly issued pollutants also remains clearly perceptible in the afternoon. Indeed the increase in traffic during the late afternoon rush-hour hardly has any impact at all. The horizontal and vertical air exchange assure a relatively fast thinning of the ozone-decomposing pollutants. First in the evening, when the wind and also the vertical transport become weaker, the ozone concentration decreases greatly, accelerated by the nitrogen oxide emission of the persistent motor vehicle traffic in the evening. That this quiets down considerably in the second half of the night can be recognized at the light increase of the ozone at the city expressway. The ozone concentration above the near ground cold air layer has remained unaffected. The negligibly decreasing ozone level yields a reservoir for a further rise at the next day.

In this connection long-term trends of the ozone concentration will be discussed briefly. From Figure 8 it is obvious that in the relatively short measuring period in Berlin the average maximum value on summer days indicates no significant trend.

Figure 8
Fig. 8: Median Value of the Daily Ozone Maximums on Summer Days

Excel
[Statistical base of Figure 8 is also available as Excel-File (MS-Excel is required).]

Indeed a 1 to 2 % increase in the ozone concentration per year since the mid- 70s is to be assumed for other stations, particularly far away from conurbations, e.g. on the Zugspitze (cf. German Bundestag 1990). This increase of the wide area background concentration is probably due particularly to the rise in traffic emissions in the 70s and 80s. Whether for instance the decline of the hydrocarbon output brought by the decommissioning of two-stroke vehicles in the new federal states will provide an improvement in the ozone burden in Berlin can first be answered in a few years.

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