A study examining the dangers of emissions has begun in California at the behest of one of California's leading pollution control agencies - the South Coast Air Quality Management District (SCAQMD).

The Multiple Air Toxics Exposure Study III (MATES III) will seek to test the levels of cancer-causing toxic air pollutants and evaluate the risk they pose to residents of Southern California.

One of the main areas of focus will be the level of diesel particulate, which was the key finding of the original MATES study.

The original survey was held up as crucial evidence for the risk of unfettered automotive development, which was then built on by the second test.

MATES II identified particulate emissions - attributed mostly to diesel engines - as an important cancer risk factor.

Diesel particulates were said to account for about 70 per cent of the total cancer risk, underlining the significance of the autocatalyst market and other alternative forms of emissions control.

The SCAQMD said that the original test was crucial in developing the strategy for tackling cancer-causing emissions, with a series of automotive regulations issued since the project.

The MATES III study, which is expected to begin this month, is expected to shed more light on the effectiveness of these regulations and serve as a tool in shaping future air quality policies.