Health-Based Federal and State Standards

Based on health considerations, both the state and the federal government set ambient air quality standards for PM10, and more recently, these standards have been revisited to address the health-related concerns regarding PM2.5.  In general, the air quality standards developed were determined by level of exposure to an airborne pollutant without experiencing adverse health effects.

The health- and welfare-based standards for particulate matter were last revised in 1987. The NAAQS for PM10 replaces older particulate standards based on total suspended particulates (TSP) in the atmosphere.  In 1987, the EPA replaced the TSP standards because particulate matter of less than 10 microns diameter contained in a cubic meter of air (mg/m3) that can be inhaled deeply into the lungs has greater health effects than larger particles.  Under certain circumstances some particles less than 10 microns may never be removed from the lungs by exhaling, and such particles may be carriers of other toxic materials which can be absorbed by the blood and carried to other parts of the body.  The federal health standard for PM10 is set at 150 mg/m3 averaged over a 24-hour period, and 50 mg/m3 for an annual average.

The California 24-hour and annual average standards are considerably more stringent than the federal 24-hour and annual average standards.  The ARB revised the standard for the annual average in 2002, pursuant to the Children’s Environmental Health Protection Act.  The 24-hour PM10 standard is 50 mg/m3 (however, ARB is currently reviewing the standard) and the revised annual standard is 20 mg/m3 (changed from 30 mg/m3).  In addition, the ARB adopted a standard for PM2.5, set at 12 mg/m3 for an annual average.

The ARB and the State Department of Health Services adopted the more stringent standards because serious health effects were found to occur at PM10 levels well below the national 24-hour standard.  The standards were developed with the intention of preventing excess deaths from short-term exposures and exacerbation of symptoms in sensitive patients with respiratory disease.  In addition, the state standards were developed with the intent to prevent excess seasonal declines in pulmonary function, especially in children.

In developing these standards, the ARB and the Department of Health Services reviewed many sources of health effects data, including epidemiological, biochemical, and clinical studies of controlled human exposures, animal toxicology, and short-term bioassay.  The development of the final standards focused primarily on epidemiological studies.