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California MATES IV study: Cancer risk from air toxics reduced by 65%

14 October 2014

California’s South Coast Air Quality Management District (SCAQMD) has released a Draft Report from the Multiple Air Toxics Exposure Study IV (MATES IV)—a comprehensive air quality study focused on the carcinogenic risk from exposure to air toxics in the California South Coast Air Basin. Based on the exposure levels from the 10 monitoring sites used in the study, the average cancer risk from air toxics in the South Coast Air Basin is 67% lower than the estimated risk from the 2004-2006 time period.

The MATES IV Study included a monitoring program, an updated emissions inventory of toxic air contaminants, and a modeling effort to characterize risk across the South Coast Air Basin. The study is a follow-up to the MATES III study completed in 2008.

The study measured 37 substances, including PM10, PM2.5, several organic compounds (formaldehyde, benzene, toluene, PAHs,...), heavy metals (Mn, Cu, Pb, Ni,...), and other compounds. Two new substances—black carbon (BC) and ultrafine particles (UFP)—not monitored in previous MATES studies were included in the MATES IV measurement program.

Concentrations of diesel particulates, singled out as a major contributor to the cancer risk, were calculated based on the measured elemental carbon (EC) exposures which were adjusted by the ratio of emissions of EC and diesel PM from the emissions inventory estimates. This indirect method of estimation of diesel PM exposures is one of the major sources of uncertainty in the study.

Although the estimated Basin-wide risks declined from the MATES III period, areas near the ports and near transportation corridors continue to show the highest air toxics risk, emphasized the authors of the MATES IV study. Some of the key findings of the study are:

Figure 1 shows the average concentrations of diesel particulate matter modeled by the study. The highest concentration of diesel PM2.5—2.9 μg/m3—was simulated to occur around the Ports of Los Angeles and Long Beach.

Figure 1. 2012/2013 Annual Average Concentrations of Diesel PM2.5 Modeled by MATES IV Study

Diesel PM exposures have been significantly reduced from the 2004-2006 period, due to the various diesel emission regulations and programs enacted in California and federally in the United States. In the previous MATES III study, the average ambient diesel PM concentration in the South Coast Basin was estimated at 3.2-3.49 µg/m3.

SCAQMD has released the Draft Report for a 90-day review period and will accept comments until January 5, 2015.

Source: SCAQMD