The Case for a 24-Hour PM2.5 Standard
In November 2001, the California Air Resources Board (ARB) and the Office of Environmental Health Hazard Assessment (OEHHA) released a staff paper for public comment which recommends a stringent new annual average standard for fine particles (PM2.5), but makes no recommendation on a short-term, 24-hour standard.
The staff paper also recommends substantially tightening the annual average PM10 standard, and retaining the existing 24-hour PM10 standard.
The staff paper claims that evidence of strictly short-term effects of particulate exposures is not compelling (that effects are more likely a result of chronic exposures), and that if short-term effects are of concern, they will be prevented by compliance with an annual average standard.
The American Lung Association® disagrees, and urges establishment of a strict 24-hour PM2.5 standard to protect sensitive populations from the harmful effects of short-term peak exposures to fine particle pollution.
· Three dozen time-series epidemiological studies from across the globe have reported associations between increases in daily concentrations of various measures of particulate matter, and increases in daily death counts, particularly death from cardiac and respiratory causes. The life-shortening demonstrated by these studies is on the order of months to years.
· A sophisticated large-scale study of 90 U.S. cities, specifically designed to address issues of confounding by other pollutants and multiple other factors, confirmed that exposure to daily increases in particulate air pollution concentrations is associated with mortality. (HEI, 2000, “National Morbidity, Mortality, and Air Pollution Study”)
· Several hundred community health studies have demonstrated associations between daily exposure to PM and a cascade of health outcomes, ranging from hospitalization for cardiovascular or respiratory causes, emergency room visits, asthma exacerbation, acute and chronic bronchitis, restrictions in activity, work loss, school absenteeism, respiratory symptoms, and decline in lung function.
· An EPA risk analysis for Los Angeles demonstrated that on 35 percent of the days when air quality is monitored, concentrations would be in the hazardous range even after attaining EPA’s annual average standard for PM2.5. The largest portion of the health risks associated with daily exposures to particulate pollution are not prevented by an annual standard.
· An American Lung Association® analysis of 1999 fine particle monitoring data indicates that EPA’s annual average standards do not protect against peak concentrations in major cities across the country including in San Jose, San Francisco, and Oakland. An annual average standard alone places no limits on how high daily concentrations can rise, leaving the public unprotected on precisely the days when adverse health effects are most likely to be experienced.
A short-term standard is the only mechanism that will ensure protection against sources of short-term peak concentrations, such as occur during temperature inversions, or from seasonal sources such as wood stoves and certain industrial operations.
