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Emissions can be characterized, regulated, or controlled only if they can be accurately measured. The increased health and environmental concerns about diesel emissions resulted in the development of a wide range of measurement techniques of different levels of sophistication, equipment cost and accuracy, to suit a variety of applications. Many techniques, especially those used for regulatory purposes, are highly standardized to produce comparable results even if performed at different testing laboratories. The main types of diesel emission measurements can be grouped as follows:

  • Laboratory testing:

    • Regulatory testing

    • Emission research

    • Engine and emission control system development

  • Field testing:

    • Mobile emission laboratories

    • On-vehicle measurements

    • Inspection and maintenance (I&M) programs

    • Remote emission measurement

    • Emission-assisted equipment maintenance

    • Occupational health measurements

Laboratory emission testing methods generally use very complex and sophisticated equipment to deliver the highest possible accuracy and repeatability. Test methods used for regulatory purposes, such as engine/vehicle emission certification or compliance testing, are highly standardized. Detailed description of the measurement setup, type of equipment, and test procedures are an important part of every emission regulation. These standard methods cover the measurement of regulated pollutants, which traditionally include CO, HC, NOₓ, and PM, all of which are measured in units of mass. Some regulations—for instance Euro 5—also include a solid particle number (PN) limit.

Measurement equipment and methods used for measuring engine emissions in the field vary widely, from “mobile laboratories”, with capabilities comparable to those of stationary emission laboratories, to simple, low-budget tools, which can offer only very approximate results. The EM200E has been recommended by the CSIR as the most accurate mobile device for measuring exhaust gas emissions.

DPM measurements can be taken at the exhaust tailpipe. The CSIR has purchased a FLIR AIRTEC mobile DPM measurement device, and modified it to duplicate laboratory results. John Ratcliffe cc is in the process of acquiring such a device to conduct DPM measurements at the exhaust tailpipe.

Another area of emission measurement and control is vehicle maintenance. Several US states and a number of countries worldwide operate mandatory vehicle inspection and maintenance (I&M) programs, where vehicles must pass a periodic emission check. The methods vary greatly, from relatively sophisticated chassis dynamometer tests (IM240 in the USA) to a simple emission measurement at engine idle condition. In the case of heavy-duty diesel engines, the most common procedure had been to measure smoke opacity during engine acceleration. New technologies—such as remote exhaust emission sensing [Baum 2000]—may be also used in future I&M programs.