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EPA Proposes Major Revisions to Particulate Matter Standards

County-level 24-hour average PM2.5, 2001-2003. Under the new regulations, areas with PM2.5 > 35µg/m3 would be in violation.

The US Environmental Protection Agency (EPA) is proposing major revisions to its national air quality standards for fine particulate matter (PM) and from some coarse particles, strengthening the first by 46% and the second by 53%.

This is not an adjustment of vehicle emissions standards—but the tighter air quality standards may at some point reflect back on new emissions standards or policies for retrofitting or culling the vehicle population. Some German cities, for example, are considering a ban on older diesels to meet PM requirements. (Earlier post.)

Numerous studies have associated fine particulate matter with a variety of respiratory and cardiovascular problems, ranging from aggravated asthma, to irregular heartbeats, heart attacks, and early death in people with heart or lung disease. (Earlier post.)

The proposed revisions will address two categories of particulate matter: fine particles which are 2.5 micrometers in diameter and smaller (PM2.5); and “inhalable coarse” particles, which are between 2.5 and 10 micrometers (PM10–2.5). EPA has had national air quality standards for fine particles since 1997 and for coarse particles 10 micrometers and smaller (PM10) since 1987.

For each category of particulate matter, the proposal includes two types of standards: primary standards, to protect public health; and secondary standards, to protect the public welfare such as crops, vegetation, wildlife, buildings and national monuments and visibility.

Fine Particles. EPA currently has two primary standards for fine particles: an annual standard, designed to protect against effects caused by short-term exposure (days or weeks) and longer-term exposure (seasons to years); and a 24-hour standard, designed to provide additional protection on days with high peak PM2.5 concentrations. The proposals are:

  • PM2.5 Primary (Health-related) 24-Hour Standard

    • Strengthening the 24-hour fine particle standard from the current level of 65 micrograms per cubic meter (µg/m3) to 35 µg/m3—a decrease of 46%.

    • EPA also is soliciting public comment on alternative levels for the 24-hour standard, between the range of 35 and 30 µg/m3. In addition, the Agency will take comment on: retaining the current level of the standard (of 65 µg/m3), on levels as high as 65 µg/m3 and as low as 25 µg/m3; and on alternative approaches for selecting the level of the standard.

    • Compliance. An area would meet the 24-hour standard if the 98th percentile of 24-hour PM2.5 concentrations in a year, averaged over three years, is less than or equal to the level of the standard EPA sets in its final rule (35µg/m3 under this proposal). This is the same form as the current 24-hour standard.

  • PM2.5 Primary (Health-Related) Annual Standard

    • Retain the standard at 15µg/m3 based on the assessment of several expanded, re-analyzed and new studies that have increased the Agency’s confidence in associations between long-term PM2.5 exposure and serious health effects.

    • EPA is considering and is seeking broad public comment on the range of 15µg/m3 down to 13 µg/m3 which is the lower end of the range CASAC (Clean Air Science Advisory Committee) recommended. EPA also is soliciting public comment on an alternative level for the annual standard of 12 µg/m3.

    • Compliance. An area would be in compliance with the annual PM2.5 standard when the three-year average of the annual average PM2.5 concentration is less than or equal to 15 µg/m3 (or whatever level of standard EPA sets in its final rule). This is the same form as the current annual standard. Current fine particle standards allow some areas to average measurements from multiple community-oriented monitors to determine compliance with the annual standard. The proposed revisions also would limit the conditions under which this averaging could take place. EPA also is seeking public comment on no longer allowing averaging measurements from multiple community monitors.

  • PM2.5 Secondary Standards

    • Setting the secondary standards for both the annual and 24-hour standards at levels identical to the primary standards.

    • EPA also is taking comment on whether to set a separate PM2.5 standard, designed to address visibility (principally in urban areas), on potential levels for that standard within a range of 20 to 30 µg/m3, and on averaging times for the standard within a range of four to eight daylight hours.

Coarse particles. EPA set the current standards for coarse particles (PM10) in 1987. These standards—a 24-hour standard of 150 µg/m3, and an annual standard of 50 µg/m3—apply to particles 10 micrometers in diameter and smaller.

The proposed revisions would change the definition of the standard so that it covers only particles between 10 and 2.5 micrometers in diameter (PM10–2.5). The proposed standards are:

  • PM10–2.5 Primary (Health-Related) 24-hour standard

    • Setting the 24-hour standard at 70 µg/m3—a decrease of 53%.

    • EPA would further define PM10–2.5 to include only those coarse particles that come from sources such as high-density traffic on paved roads, industrial sources and construction activities—the kinds of coarse particles typically found in urban areas. The proposed standard would not cover situations where the coarse particles in the air come from sources such as windblown dust and soils, agricultural sources and mining sources.

    • EPA is proposing to revoke the current 24-hour PM10 standards, except in areas that have 1) violating monitors; and 2) a population of 100,000 or more. These standards would remain in place in these areas until the Agency has completed attainment and nonattainment designations for PM10–2.5.

    • EPA is taking comment on whether the 24-hour PM10 standards should be retained in smaller areas (population less than 100,000) that are dominated by one or more large industrial sources.

    • EPA is also taking comment on whether it should: 1) retain the current PM10 standard in place of the proposed PM10–2.5 standard or 2) not establish a coarse fraction PM standard at this time pending the development of a coarse fraction monitoring network and further research on the health effects of coarse particles.

  • PM10–2.5 Primary (Health-Related) Annual Standard

    • EPA is not proposing an annual standard for PM10–2.5.

  • PM10–2.5 Secondary Standards

    • Under the proposal, the secondary 24-hour standard for PM10–2.5 would be identical to the primary standard.

    • Compliance. An area would meet the coarse particle standard if the 98th percentile of 24-hour PM10–2.5 concentrations in a year, averaged over three years, is less than or equal to the level set in the final rule (70µg/m3 in this proposal). This form will provide a more stable target for air pollution control programs by reducing the impact of unusual weather conditions, such as high wind events.

In a separate but related action, EPA is proposing amendments to its national air quality monitoring requirements, including those for monitoring particle pollution. The proposal would change the locations of some types of monitors, add new monitors for some pollutants, and allow states to shut down unneeded monitors for some pollutants.




Mike, is there some sort of "brief" analysis of that map? I'm particularly interested in California, where LA actually happens to be once of the cleanest regions of the state.


Brief? No. :-) The 500+ page staff report cited in the Resource section has more detail down to the different metro areas for both types of particles, but you have to extract it.

For example, a summary of PM2.5 data from the Los Angeles-Long Beach-Riverside, CA area:
No. of sites: 22
3-yr average annual mean levels (micrograms/m3) (2001-2003):
Area average: 19.0
Max site: 27.8
Min site: 9.9
Largest diff, any site vs. average: 48%
Max site vs. min site: 64%
r Max site vs. min site: 0.50


thanks for the info. my interest was though, did they do an analysis of sources? i mean it's great to see the data, but i'd also love to find out why LA has under 30 µg/m3, but the county just north (don't know the name) of us has over 65 µg.


It probably has a lot to do with geography and prevailing wind patterns. This is also the case for California's central valley, which is downwind from the SF Bay Area, but backed up against the towering Sierra Nevada. (Not that industrial farming within the valley isn't contributing to the problem.)

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