Berlin Environmental Atlas 03.11 Traffic-Related Air Pollution - NO2 and PM10 (Edition 2008)

The Emissions Models Primary Roads (Linear Sources) and Secondary Road Networks (Area Sources)

Exhaust emissions from motor vehicle traffic depend on factors which can be summarised as traffic-specific and motor vehicle-specific quanta.

Traffic-specific quanta are described by traffic density, i.e. the number of vehicles moving on a given section of a street (source), and their driving style (driving mode). Driving style is determined according to different street types (city centre street, secondary road, primary road with or without traffic lights, freeway), and function (shopping street, residential street, or access street).

The motor vehicle-specific quanta, generally expressed by exhaust emissions, are determined by:

• the type of engine (four-stroke, two-stroke or diesel)
• the type of carburetion (carburettor or fuel injection)
• the type of fuel (two-stroke mixture, gasoline, diesel)
• the type of purification system, if any (regulated or unregulated catalytic converter, recycling of exhaust gases); and
• other factors pertaining to the technical condition of the engine.

Emissions also depend on the driving style (driving mode), and are therefore stated for various driving styles. Cold weather starts, which lead to increased emissions during the warm-up phase of the engine, together with evaporation emissions, are considered important vehicle specific quanta.

The emissions factors are provided in the UBA Emissions Factors Manual (Version 2.1, April 2004) for each year from 1990 through 2020. It lists the emission factors for all relevant emitted substances for each vehicle group (passenger cars, light commercial vehicles, motorised two wheeled vehicles, busses and heavy commercial vehicles), for currently at least five reduction levels (1980s ECE cycle, Euro I, Euro II, Euro III, Euro IV, Euro V - only for heavy commercial vehicles), and for each type of street.

The stricter exhaust standard Euro 5 for cars is stipulated as mandatory for new vehicles as of September 2009. However, the planned stricter standard Euro VI for heavy commercial vehicles and Euro 6 for cars will very likely become effective only as of 2013. These exhaust standards cannot be taken into account with the present version of the UBA manual, so that realistic forecasts of motor vehicle emissions are only possible through 2010, and to a limited degree through 2015.

Ascertainment of Emissions from Abrasion and Air Movement Caused by Street Traffic

With today's knowledge, it is assumed that a large part of traffic related PM10 emissions do not originate from vehicle exhaust, but rather from the wind stirring up the particulate matter lying on the street surface, and from tyre and brake abrasion.

The calculations of these emissions with IMMIS^em/air are based on the modified EPA formula from corresponding investigations. This formula was developed from measurements taken on Schildhornstrasse and on Frankfurter Allee, and is based on the finding that approximately 50 % of the measured additional particulate in canyon streets in not attributable to motor vehicle exhaust, but is rather caused by motor vehicle related abrasion (braking and street/tyre abrasion) and air movement. Since exhaust emissions have since been further reduced by improved engine technology, the proportion of additional pollution due to non-exhaust-caused emissions is today considerably higher than 50 %.

Figure 3 shows each output quantum for the calculation of exhaust and abrasion emissions from traffic, such as driving style factors, "stop and go" supplement, cold weather start factors etc., as well as the results.

Emissions from motorised two wheeled vehicles cannot be shown due to a lack of traffic counts on the primary road network. Their contribution to the total is determined on the basis of the average traffic load in Germany and available emissions data.

For areas with distinct orography, the street sections should be arranged in longitudinal categories. However, this is not necessary for Berlin.

Emission Model Secondary Roads Networks (Area Sources)

The traffic pollution on secondary roads for 2005 was calculated with the aid of the traffic routing programme VISUM, based on the underlying source-goal relationship. The resulting total driving performance and the proportion of heavy commercial vehicles was assigned to traffic cells in the city. The emissions from exhausts, ,and from dust stirred up by wind and from abrasion in secondary roads, was determined using the IMMIS^em/air emissions module.

In secondary roads networks, emissions are not calculated for specified sections of streets, but rather as grids per square kilometre. The driving performance for the grids is determined on the basis of:

• predominate use of the area, either
  • residential areas in the outskirts;
  • commercial and industry; or
  • inner city and sub centres
• the number of residents and jobs is categorised as
  • trade and service jobs, or
  • manufacturing,
• the results are in source/goal matrices of motor vehicle traffic.

Further inputs for determining total emissions of each pollution component for each area correspond to those for the calculations in the primary roads network.

Exhaust and Abrasion Emissions in the City

Table 3 breaks down the driving activity caused by motor vehicle traffic in the city of Berlin (millions of vehicle kilometres per year); fuel use (t) and the exhaust and abrasion emissions of vehicular traffic (t/year), by type of vehicle, for the reference year 2005.

The new method of measuring emissions for this registry is also a suitable basis for dispersion calculations to determine the extent of pollution at streets. The extensive reorganisation of calculation methods permits only very limited comparisons with previous emissions increases, because these were based on a much simpler method of calculation.