Traffic-related Air Pollution - Hydrocarbons 1993
Cadastre of Motor Traffic Emissions
The Berlin Department of Urban Development, Environmental Protection and Technology (SenStadtUmTech – Senatsverwaltung für Stadtentwicklung, Umweltschutz und Technologie) maintains a cadastre of emissions for the major groups of polluters, including the polluter group of motor vehicle traffic.
The 1993 Cadastre of Motor Vehicle Traffic Emissions gives the first unified picture of air pollutant emissions produced by motor vehicle traffic for the entire city of Berlin.
This cadastre uses a new method to calculate emissions. This method is also a suitable basis for dispersal calculations which can ascertain pollutant loads on roads. The far-reaching restructuring of calculation methodology allows only limited comparisons to be made with previous emission investigations based on much simpler methods.
Investigation of Motor Traffic Pollution
The basis is the first comprehensive traffic count, performed in 1993. This count included the primary road network as well as scheduled bus routes. This count resulted in the availability of certain data for every road segment in the primary road network:
- average daily motor traffic (DTV) in motor vehicles/day,
- average daily truck traffic in trucks/day for heavy trucks,
- percentage of busses in regular traffic.
This data was supplemented with extensive analyses of vehicle types and total travelled distances of registered motor vehicles in Berlin. The data was also supplemented by emission factors that describe these cars and utility vehicles (cf. Map 07.01 SenStadtUm 1995).
Methodology of Emission Studies
Pollutant emissions produced by motor traffic include the exhausts and abrasions of moving traffic; the evaporative emissions of stopped traffic, and evaporative emissions at fuel stations. Figure 2 presents an overview of the emission study methodology. Fuel station emissions are listed under light industry.
Emission models aided the calculation of pollutant and CO2 emissions for line sources (primary roads), and area sources (secondary roads and evaporative emissions).
Exhaust and abrasion emissions appear as line sources on primary and secondary roads. These emissions are calculated as line sources only for the primary road network because only these streets had data available from previous counts for average daily traffic values (DTV) and hourly capacity. Emissions from line sources are classified as area values in the grid system. Emissions for the secondary road network, however, are directly deduced from the seperate grids from assumptions made about traffic volumes and amounts of trucks.
Hydrocarbon evaporative emissions occur from pressure differences between the fuel tank and the carburetor float chamber. They occur
- in non-moving motor vehicles resulting from daily temperature fluctuations (tank respiration emissions),
- in hot engines after long distances,
- in warm engines after short distances.
Evaporative hydrocarbon emissions and benzol fractions are also determined for the grids. Evaporative emissions resulting from refueling are also calculated. Evaporative emissions from moving traffic could be neglected because they are very low.
Emission Models for Primary Road Networks (Line Sources) and Secondary Road Networks (Area Sources)
The emission simulation model EMISS helped calculate pollutant and CO2 emissions (cf. Map 08.03 CO2 Emissions, SenStadtUmTech, in preparation), and fuel consumption for traffic on primary road networks.
Figure 3 shows the individual model parameters, including total travelled distance factors, stop-and-go formulas, cold start factors, etc., and the results. The methodological background is described in detail in Liwicki, Garben 1993.
Emissions for motorized two-wheel vehicles could not be ascertained because traffic counts do not exist. Two-wheel vehicle contribution to total emissions are calculated on the basis of total travelled distances in Germany, and on available emission factors.
Road segments in areas of varying topography are classified according to longitudinal inclines; but this is not necessary for Berlin.
Emission Model for Secondary Road Network (Area Sources)
Emissions in the secondary road network are not calculated for each specific road segment. Emissions are calculated for a grid area of 1 km2. Travelled distances within the grid surface area are estimated based on the following data:
- predominant use of the area, subdivided into:
- residential living in outer areas of the city,
- small business and industrial areas,
- inner city and suburban areas,
- number of inhabitants and positions of employment, differentiated according to:
- commercial and service industry,
- manufacturing industry,
- and motor traffic source-goal-matrices derived from the above.
It can be assumed that significant traffic jams do not occur in the secondary road network. “Stop and go” supplements are not added to the calculations. Daily, weekly and annual matrices for the secondary road network were then not necessary.
Further input variables needed for determining total emissions for each pollutant component in each grid area correspond to the input variables used for calculating total emissions in the primary road network.
Refueling emissions are determined based on permit-registered fuel stations and their fuel turnovers.
1.4 g of HC per liter of carburetor fuel are emitted at fuel stations with no fuel vapor recovery systems. The fuel vapor recovery system returns 80 % of emitted amounts.
HC emissions from the preliminary chain are not given: these emissions include the transfer of fuel from 1) tanker trucks, tanker ships and railroad tank cars to the fuel depot; from 2) the fuel depot to the tanker; and from 3) the tanker to the fuel station.