BAB II: a project to evaluate the accuracy of real-world traffic emissions for a motorway

To ensure the efficiency of strategies to reduce air pollutants caused by road traffic, it is essential to evaluate the emission data to be used in emission calculation models. This basic approach of the BAB II project (BundesAutoBahn––federal highway) has been reached by simultaneous measurements of gaseous and particulate emissions on the windward and lee side perpendicular to a motorway. The differences between the measurements allows for the calculation of the emissions caused by traffic on the motorway. Measurements of CO, NO, NOx, CO2, O3, VOC, and particulates of high horizontal and vertical resolution were made. The experimental setup was made symmetric to the motorway, with 52 m high towers on each side. The field phase took place from 1 to 25 May 2001 at the motorway A656 near Heidelberg, Germany. In cases of wind direction perpendicular to the motorway, the height of the plume caused by traffic emissions is detectable and the emissions released on the motorway can be calculated. With traffic census carried out simultaneously, the emission data can be estimated using emission factors given in the literature. Comparison between real-world traffic emissions and calculated emissions allows for an evaluation of the emissions calculated by the models.This paper gives an overview of BAB II, its measuring concept, the experimental setup, and the quality assurance and control program. It is shown in detail that the method of emission estimation by measurements of concentration differences between both sides of a motorway works quite well if the meteorological assumptions for determining real-world traffic emissions have been fulfilled. Detailed results in terms of measured and model-calculated emissions of gaseous and particulate species will be reported in a number of subsequent papers.