Very Fine Particulates
U.S. Environmental Protection Agency (EPA) has just proposed updates to its national air quality standards for harmful fine particle pollution, including soot (known as PM2.5). These microscopic particles can penetrate deep into the lungs and have been potentially linked to a wide range of serious health effects, including premature death, heart attacks, and strokes, as well as acute bronchitis and aggravated asthma among children. A federal court ruling required EPA to update the standard based on best available science. The current proposal, which meets that requirement, builds on steps already taken by the EPA to slash dangerous pollution in communities across the country. Thanks to these steps, 99 percent of U.S. counties are projected to meet the proposed standard without any additional action.
Air is filled with very small particulate matter or dust. One can see it in a ray of sunlight on an otherwise perfectly clear day. It has many different shapes and many different chemical compositions.
Particulates (sometimes referred to as soot)are tiny subdivisions of solid matter suspended in a gas or liquid. In contrast, aerosol refers to particles and/or liquid droplets and the gas together.
The size of the particle is a main determinant of where in the respiratory tract the particle will come to rest when inhaled. Because of their small size, particles on the order of ~10 micrometers or less (PM10) can penetrate the deepest part of the lungs such as the bronchioles or alveoli. Larger particles are generally filtered in the nose and throat via cilia and mucus, but particulate matter smaller than about 10 micrometers, referred to as PM10, can settle in the bronchi and lungs and cause health problems. Similarly, particles smaller than 2.5 micrometers, PM2.5, tend to penetrate into the gas exchange regions of the lung, and very small particles (< 100 nanometers) may pass through the lungs to affect other organs.
A study published in the Journal of the American Medical Association indicates that PM2.5 leads to high plaque deposits in arteries, causing vascular inflammation and atherosclerosis — a hardening of the arteries that reduces elasticity, which can lead to heart attacks and other cardiovascular problems. Researchers suggest that even short-term exposure at elevated concentrations could significantly contribute to heart disease. A study in The Lancet concluded that traffic exhaust (something fairly hard to avoid) is the single most serious preventable cause of heart attack in the general public.
EPA’s proposal would strengthen the annual health standard for harmful fine particle pollution (PM2.5) to a level within a range of 13 micrograms per cubic meter to 12 micrograms per cubic meter. The current annual standard is 15 micrograms per cubic meter. The proposed changes, which are consistent with the advice from the agency’s independent science advisers, are based on an extensive body of scientific evidence that includes thousands of studies — including many large studies which show negative health impacts at lower levels than previously understood. By proposing a range, the agency will collect input from the public as well as a number of stakeholders, including industry and public health groups, to help determine the most appropriate final standard to protect public health. It is important to note that the proposal has zero effect on the existing daily standard for fine particles or the existing daily standard for coarse particles (PM10), both of which would remain unchanged.
Thanks to other recent Clean Air Act rules that EPA has either proposed or set, EPA has estimated these will dramatically cut pollution, 99 percent of U.S. counties are projected to meet the proposed standards without undertaking any further actions to reduce emissions.
Depending on the final level of the standard, EPA estimated benefits will range from $88 million a year, with estimated costs of implementation as low as $2.9 million, to $5.9 billion in annual benefits with a cost of $69 million — a return ranging from $30 to $86 for every dollar invested in pollution control. While EPA cannot consider costs in selecting a standard under the Clean Air Act, those costs are estimated as part of the careful analysis undertaken for all significant regulations, as required by Executive Order 13563 issued by President Obama in January 2011.
EPA will accept public comment for 63 days after the proposed standards are published in the Federal Register. The agency will hold two public hearings; one in Sacramento, CA. and one in Philadelphia, PA. Details on the hearings will be announced shortly. EPA plans to issue the final standards by December 14, 2012.
For further information see Soot.
Atmospheric Particulates image via Wikipedia.