Verein Deutscher Ingenieure

Measurement of soot (Ambient Air) - Thermographical determination of elemental carbon after thermal desorption of organic carbon
 N VDI 2465 BLATT 2

Annotation

Introduction

In spite of the considerable decrease the emissions from motor vehicle traffic are a major source of air contamination in inner cities [1]. These emissions are becoming of special relevance to air quality in particular because of the closeness between the emitter and the receiver in street canyons with a high traffic density.

To reduce the soot emissions which are considered to be carcinogenic the 23rd Ordinance on the Implementation of the German Federal Air Pollution Control Act BImSchG (Article 40 Section 2) established, amongst other things, an annual mean concentration as a criterion for assessing soot due to motor vehicles [2]. At the moment soot is essentially emitted by motor vehicles run by diesel engines.

Soot is generally composed of elemental carbon and primary emissions of organic carbon Compounds. Elemental carbon is thus an important indicator of products of incomplete combustion processes. The method described in this Guideline defmes elemental carbon as the proportion of total carbon which, following thermal desorption of organic carbon Compounds, is measured by subsequent combustion.

There are currently no suitable source-specific index substances for routine analysis of diesel soot. Also, the chemical and physical changes undergone by the particles when they pass through atmospheric aging processes do not permit soot particles to be differentiated according to their source (traffic, domestic fires, industry) by chemical analysis. When air pollution due to soot from motor vehicles is measured and evaluated, it must therefore be possible to assume that soot emissions from other combustion processes are negligible at the measurement point, or are quantifiable, for example on the basis of emission factors.