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Berlin Environmental Atlas

03.09 Traffic-related Air Pollution - Hydrocarbons

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Map Description

The Berlin primary road network has a length of 1,163 km. The daily travelled distance on this network totals 30,000,000 vehicle kilometers. This figure is almost 100 times the earth's circumference. The secondary road network is about 4,000 km long, and the daily travelled distance is only about 5,600,000 vehicle kilometers. Figure 5 depicts the percentual distribution of exhaust and abrasion emissions of various pollutants according to the Berlin primary and secondary road networks. It is conspicuous that an extremely high percentage of hydrocarbon and benzol emissions occur on the secondary road network. These emissions are strongly influenced by cold start factors; and about half of the initial kilometers travelled after a start occur on secondary roads.

Fig. 5: Percentual Distribution of Emissions and Distance Travelled in Berlin (Liwicki, Garben 1993)

Hydrocarbon Emissions in Primary Road Network

Map 03.09.1 shows that the primary long outbound arterial roads stand out with particularly high exhaust gas emissions at 1) the city expressway ring (Stadtautobahnring), 2) along the east-west axis on roads such as Bismarckstrasse to Kaiserdamm in Charlottenburg, and Karl-Marx-Allee to Frankfurter Allee in Mitte and Friedrichshain and 3) other primary arterial roads. Emission loads over 50 kg/m and 50 t/km have been measured at these roads. The significant impact of these main emission segments are clearly to be seen in a comparison with the highest grid value (150 t/km²·a) in Map 03.09.2, Exhaust Gas Emissions on the Entire Road Network. These primary roads have about 6 % of area on a 1 sq km grid; their emission values are about 30 %.

Emission level evaluations show clear correlation to traffic volume, insofar as the characteristics of individual roads are taken into consideration. Most of the 70 km-long expressway falls into the highest emission categories. The AVUS segment starting at the Funkturm (broadcast tower) triangle, however, has a traffic volume of over 70,000 vehicles a day, and shows a relatively lower pollutant load of 13 kg/m·a. This is due to a relatively undisturbed traffic flow.

Exhaust Gas Emissions in Entire Road Network

Distance travelled on the primary road network is about five times greater than distance travelled on the secondary road network. This 5:1 ratio is not reflected in the amounts of hydrocarbon emissions on the two road networks. This disproportion can be seen in Map 03.09.2 - Exhaust Gas Emissions in Entire Road Network. All grid areas within the inner ring of the City Rail Circle Line (S-Bahn-Ring) have over 50 t/km²·a. The influence of individual long avenues is no longer so clear. 1993 pollutant loads in areas of West Berlin were greater than in East Berlin, but this difference should have evened out by now. East Berlin motor vehicle registrations and distances travelled have increased, and are now near western levels. Other local centers outside the inner city with over 50 t/km²·a have emerged in the boroughs of Spandau, Reinickendorf, Marzahn, Treptow and Neukölln.

Volatile hydrocarbon requires that fuel tank evaporation be considered separately from the direct emissions produced by moving vehicles. The fuel tank respiration of non-moving motor vehicles are differentiated from evaporative effects resulting from use; i.e. hot and warm motors. Map 03.09.3 gives parked motor vehicle vapor emissions and Map 03.09.4 gives evaporative emissions based on hot and warm engines.

Evaporative Emissions from Tank Respiration

Even vehicles parked and not driven for a day can produce hydrocarbon emissions through tank respiration. Tank respiration results from pressure differences between the fuel tank and the carburetor float chamber. Pressure differences are caused by temperature fluctuations. It has been calculated that tank respiration produced 1,830 tons of hydrocarbon emissions in Berlin in 1993. This is a good 5 % of total emissions. These tank respiration emissions could have been prevented and used for fuel if vehicles had been equipped with activated carbon filters.

The distribution of emission levels in the various grids reflects both population density and the ratio of vehicles to residents. Residential areas in outlying areas, some borough centers, and the densely built inner city stand out.

Evaporative Emissions from Vehicles after Use / Hot Engines and Warm Engines

Hot and warm engine evaporative emissions are produced when engine and exhaust systems heat the fuel contained in fuel-feed lines after the engine is shut off. Hot and warm engine evaporative emissions reach levels of 6,600 tons; much greater than tank respiration emissions. Hot and warm engine evaporative emissions are a decisive influence on the distribution of total motor vehicle evaporative emissions (Map 03.09.5 - Total Evaporative Emissions of Motor Vehicle Traffic). Cars, station wagons and light utility vehicles with conventional internal combustion engines (Otto engines) produce these evaporative emissions when their engines are switched off - this occurs about 3,270,000 times a day in Berlin. The grids with the highest levels of over 50 t/km²·a are within the inner city. The inner city is the most frequent destination for traffic - for work, recreation, and shopping. But some local centers, such as Schlossstrasse in Steglitz, have registered loads of around 30 t/km²·a. These local centers are well above the average Berlin load of 7 t/km²·a.

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