AirWare On-line Manuals: Emission factors traffic

AirWare On-line Reference Manual

Release Level	5.3.0 beta
Release Date	2007 06
Revision Level	1.1

Emission factors: traffic

Emissions for traffic sources are taken by the models from the emission data base, associated with each line source for any or all pollutants considered.

The emission values are either directly entered with the respective soucre, or can be estimates from source specififc data on

vehicle class (defined in the fleet composition object)
average speed over a segment
traffic frequency over all classes
road type or category and road type correction factor
coald start fraction and correction factor
data base tables of vehicle class, speed, and pollutant specific emission factors
correction factors for cold starts and road type.

together with the temporal emisison patterns

The calculation strategy

The basic emission estimates are simple: the emisison factor defines the amount of pollutant generated ( in g/km) from a single vehicle of the gfiven category in the given speed range. This is then converted to the required emission unit of g/ms per segment by correcting for the number of vehiclea and their distribution, segment length, and average speed. Optional corrections for colds start trips and road type can be applied.

The emission inventory primarily uses direct emission estimtes; If and only IF no direct emission estimate is in the data base (for any or all of the pollutants), the estimation is attempted IF and only IF all necessary data for indirect estimation are defined. Then, whenever the emission inventory is recalculated (the button: RECALCULATE) is pressed) missing, undefined emission values will be replaced with the emission factor derived estimates wherever possible. Estimated values are marked in the display of individual OBJECT (line source segments)

Emission factor editing

The Emisison factors can be edited directly in the data base for a set of matrices that are defined

For each vehicle class (user defined in the Descriptor vehicle_class the Knowledge Base) the user can add or delete vehicle classes as required;

a matrix is defined by

The set of speed classes, defined by the user as upper and lower bounds in the data records;
The set of pollutants considered is again user defined in a Descriptor in the knowledge base. The standard set includes:
- CO, CO2, NO, NOx, NO2, PM10, PM2.5, VOC.

The data base structure is defined as follows:

Database:       AIR
Table:             EMISSION_FACTOR

Structure:
ID            int(10) unsigned
DESCRIPTOR    varchar(64)
VALUE         varchar(255)
primary key   (ID, DESCRIPTOR)

Valid descriptor/ value pairs are:

LOCATIONID=53
NAME=Text
OWNER=Text (=username)
DESCRIPTION=Text

Traffic:    CLASSID=83
   em_factor_type=traffic
   emission_factor_min_speed=int
   emission_factor_max_speed=int
   emission_factor_speed_step=int (default 30)
   Factors are stored as 'pollutant,vehicle class,speed classification (starting with 1)'
      eg."NO2,gasoline_car_pre-EURO,1, EMISSION_FACTOR"

Please note that any user defined extensions to the list of pollutants will be considered as bouyant gas. An interactive editor with optional rule based assistance and statistical analysis of the emision factors is under development.