Air Quality and Health and Welfare

2.7 Toxic Materials

2.7.4 The MATES Study
The Multiple Air Toxics Exposure Study (MATES-II) is a landmark urban toxics monitoring and evaluation study conducted for the South Coast Air Basin (Basin). It represents one of the most comprehensive air toxics programs ever conducted in an urban environment. It consists of several elements - a comprehensive monitoring program, an updated emissions inventory of toxic air contaminants, and a modeling effort to fully characterize Basin risk.

In the monitoring program, over 30 air pollutants were measured including both gaseous and particulate matter.
2.7.4-1 Pollutants Measured in MATES-II

When “carcinogenic risk” is discussed, it typically refers to the probability of a person contracting cancer over the course of a lifetime if exposed to the source of cancer-causing compounds for 70 years. In other words, a cancer risk of 100 in a million at a location means that the individuals staying at that location for 70 years have a 100 in a million chance of contracting cancer. If 10,000 people live at that location, then the cancer burden for this population will be one (the population multiplied by the cancer risk). This means that one of the 10,000 people staying at the location for 70 years are expected to contract cancer.

The key result of the MATES-II study was that the average carcinogenic risk in the Basin is about 1,400 per million people. Mobile sources (e.g., cars, trucks, trains, ships, aircraft, etc.) represent the greatest contributor. About 70% of all risk is attributed to diesel particulate emissions; about 20% to other toxics associated with mobile sources (including benzene, butadiene, and formaldehyde); about 10% of all risk is attributed to stationary sources (which include industries and other certain businesses such as dry cleaners and chrome plating operations.)

The carcinogenic risk of 1,400 per million is based on a range from about 1,120 in a million to about 1,740 in a million among the ten sites.