Primary materials found in the solid phase of diesel PM include inorganic carbon and metal ashes, while the liquids include high boiling hydrocarbons, water, and sulfuric acid. According to most legal definitions of diesel particulates and the corresponding sampling and measurement methods, diesel particulates are sampled from exhaust gases that are diluted with air and cooled, typically to 52°C. These sampling procedures have been introduced in an attempt to simulate atmospheric dilution effects on diesel emissions.
Although it is known today that the products of real life atmospheric dilutions may differ from what is sampled in a laboratory dilution tunnel, there has been a consensus in regards to the above definition among worldwide public health authorities. Accordingly, the total particulate matter traditionally includes the following fractions:
Solids (inorganic carbon, ash)
Organics (organic fraction—OF)
Sulfates (hydrated sulfuric acid, metal sulfates).
There is no such consensus, however, in diesel particulate exposure regulations in various occupational health environments. The elemental carbon (EC) definition—which excludes all organic content, sulfates, or inorganic ash—appears to become the preferred representation. Sometimes, the total carbon (TC) definition, which includes both the elemental and organic carbon but no sulfates, is also used.