The US Environmental Protection Authority (EPA) has restrictions on "Particulate Matter".

A recent Wall Street Journal op-ed piece article claims it is based on a

scientifically unsupported notion that the fine particles of soot emitted by smokestacks and tailpipes are lethal. The EPA claims that such particles kill hundreds of thousands of Americans annually.

It complains that EPA proceeded despite contrary advice from the Clean Air Scientific Advisory Committee:

But when the agency ran its claims past CASAC in 1996, the board concluded that the scientific evidence did not support the agency’s regulatory conclusion. Ignoring the panel’s advice, the EPA’s leadership chose to regulate fine particles anyway, and resolved to figure out a way to avoid future troublesome opposition from CASAC.

It goes on to say that the evidence hasn't turned up since:

the sci­en­tific case against par­tic­u­late mat­ter hasn’t im­proved since the 1990s

Is it true that the EPA's restrictions on particulate matter are not supported by evidence - even today - that particulate matter kills many thousands of Americans per year?

  • 1
    The overwhelming source of particulates in the US is agriculture ; soil preparation , harvesting, etc. To avoid losing the farm vote ,the EPA has to be very careful how they craft the rules. Commented Jul 25, 2017 at 2:10
  • Do EPA regulations have to be based on health grounds, or is the simple fact that a lot of people find something unpleasant sufficient?
    – jamesqf
    Commented Sep 4, 2017 at 18:33

4 Answers 4


It is justified with (recent) evidence.

Selectively quoting from WP:Pariculates#Health_problems, emphasis of publication dates mine:

Inhalation of PM2.5 – PM10 is associated with elevated risk of adverse pregnancy outcomes, such as low birth weight.

Sapkota, Amir; Chelikowsky, Adam P.; Nachman, Keeve E.; Cohen, Aaron J.; Ritz, Beate (2012-12-01). "Exposure to particulate matter and adverse birth outcomes: a comprehensive review and meta-analysis". Air Quality, Atmosphere & Health. 5 (4): 369–381. ISSN 1873-9318. doi:10.1007/s11869-010-0106-3.

Increased levels of fine particles in the air as a result of anthropogenic particulate air pollution "is consistently and independently related to the most serious effects, including lung cancer and other cardiopulmonary mortality."

"[...] fine particulate air pollution (PM(2.5)), causes about 3% of mortality from cardiopulmonary disease, about 5% of mortality from cancer of the trachea, bronchus, and lung, and about 1% of mortality from acute respiratory infections in children under 5 years, worldwide."

Ole Raaschou-Nielsen; et al. (July 10, 2013). "Air pollution and lung cancer incidence in 17 European cohorts: prospective analyses from the European Study of Cohorts for Air Pollution Effects (ESCAPE)". The Lancet Oncology. 14 (9): 813–22. PMID 23849838. doi:10.1016/S1470-2045(13)70279-1.

Cohen, A. J.; Anderson, Ross H.; Ostro, B; Pandey, K. D.; Krzyzanowski, M; Künzli, N; Gutschmidt, K; Pope, A; Romieu, I; Samet, J. M.; Smith, K (2005). "The global burden of disease due to outdoor air pollution". J. Toxicol. Environ. Health Part A. 68 (13–14): 1301–7. PMID 16024504. doi:10.1080/15287390590936166.

[...] 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.

Pope, C Arden; et al. (2002). "Cancer, cardiopulmonary mortality, and long-term exposure to fine particulate air pollution". J. Amer. Med. Assoc. 287 (9): 1132–1141. PMC 4037163 Freely accessible. PMID 11879110. doi:10.1001/jama.287.9.1132.

An increase in estimated annual exposure to PM 2.5 of just 5 µg/m3 was linked with a 13% increased risk of heart attacks.

Cesaroni G, Forastiere F, Stafoggia M,; Stafoggia; Andersen; Badaloni; Beelen; Caracciolo; De Faire; Erbel; Eriksen; Fratiglioni; Galassi; Hampel; Heier; Hennig; Hilding; Hoffmann; Houthuijs; Jöckel; Korek; Lanki; Leander; Magnusson; Migliore; Ostenson; Overvad; Pedersen; j; Penell; et al. (2014). "Long term exposure to ambient air pollution and incidence of acute coronary events: prospective cohort study and meta-analysis in 11 European cohorts from the ESCAPE Project". BMJ (Clinical research ed.). 348: f7412. PMC 3898420 Freely accessible. PMID 24452269. doi:10.1136/bmj.f7412.

Particulate matter studies in Bangkok Thailand from 2008 indicated a 1.9% increased risk of dying from cardiovascular disease, and 1.0% risk of all disease for every 10 micrograms per cubic meter. Levels averaged 65 in 1996, 68 in 2002, and 52 in 2004. Decreasing levels may be attributed to conversions of diesel to natural gas combustion as well as improved regulations.

Archived online document, 2008

Please check the full article for more studies and references.


I am submitting a new answer because I believe there is a gap in understanding in how these regulations work. I will try to be brief, yet thorough.

EPA regulates Particulate Matter, or PM, under the authority of the Clean Air Act Amendments (CAAA) of 1990. Specifically, there is a National Ambient Air Quality Standard, or NAAQS, which limits the PM in the ambient air below certain levels.

In order to establish a new NAAQS, EPA must go through a rule making process. The end of this process is a publication in the Federal Register. The publication for the most recent update to the PM NAAQS can be found here. Within this document (specifically, starting on page 3103), EPA publishes an extensive review of the evidence for the negative health effects of the Criteria Air Pollutant that the NAAQS is limiting. I implore you to at least look at this, before believing someone who happened to opine in the Wall Street Journal.

Here are some examples of the evidence summarized there (it's a long read):

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Our EPA is required to do almost everything in a very public and open way. All of the evidence that they consider justification for the PM limits is right here for anyone to read.

  • I've added the summaries of the evidence presented, there's clearly much more in that document however I find these are enough to give a strong example of the kind of in-depth meta-studies that EPA does.
    – Sklivvz
    Commented Jul 21, 2017 at 15:23

Odd. The CASAC also disagreed with the EPA on PM in 2006 - only they felt the restrictions were not protective enough of public health:

"The CASAC recommended changes in the annual fine-particle standard because there is clear and convincing scientific evidence that significant adverse human-health effects occur in response to short-term and chronic particulate matter exposures at and below 15 μg/m3, the level of the current annual PM2.5 standard. The CASAC affirmed this recommended reduction in the annual fine-particle standard in our letter dated March 21, 2006 concerning the proposed rule for the PM NAAQS, in which 20 of the 22 members of the CASAC’s Particulate Matter Review Panel — including all seven members of the chartered (statutory) Committee — were in complete agreement. While there is uncertainty associated with the risk assessment for the PM2.5 standard, this very uncertainty suggests a need for a prudent approach to providing an adequate margin of safety. It is the CASAC’s consensus scientific opinion that the decision to retain without change the annual PM2.5 standard does not provide an “adequate margin of safety … requisite to protect the public health” (as required by the Clean Air Act), leaving parts of the population of this country at significant risk of adverse health effects from exposure to fine PM.

Significantly, we wish to point out that the CASAC’s recommendations were consistent with the mainstream scientific advice that EPA received from virtually every major medical association and public health organization that provided their input to the Agency, including the American Medical Association, the American Thoracic Society, the American Lung Association, the American Academy of Pediatrics, the American College of Cardiology, the American Heart Association, the American Cancer Society, the American Public Health Association, and the National Association of Local Boards of Health. Indeed, to our knowledge there is no science, medical or public health group that disagrees with this very important aspect of the CASAC’s recommendations. EPA’s recent “expert elicitation” study (Expanded Expert Judgment Assessment of the Concentration-Response Relationship Between PM2.5 Exposure and Mortality, September 21, 2006) only lends additional support to our conclusions concerning the adverse human health effects of PM2.5.

Source: https://yosemite.epa.gov/sab%5Csabproduct.nsf/1C69E987731CB775852571FC00499A10/$File/casac-ltr-06-003.pdf

  • This can be cleaned up to answer the question more directly; but your post illustrates the problem with the opinion piece. He relies on 20 year old footnote, 'We need more evidence', and then ignores preceding evidence. He says the today's policy isn't needed because of the body of evidence in '96; and throw in conspiracy for spice. "Regulations against cigarettes are not needed because didn't have the evidence in the 1940s."
    – RomaH
    Commented Jul 18, 2017 at 20:48
  • The author addresses this in the article, his theory is that CASAC had been infiltrated in the mean time "By the mid-2000s, the agency had entirely flipped the composition of the advisory board so two-thirds of its members were agency grantees. Lo and behold, CASAC suddenly agreed with the EPA’s leadership" - archive.is/bz4DE
    – daniel
    Commented Jul 19, 2017 at 22:56
  • 1
    That is borderline conspiracy talk. Just because they get grants from the federal government doesn't mean it is stacked, review the work it is public. If the panel wanted to line their pockets with federal money, a conclusion of 'more research is needed' would achieve that goal better than predetermined conclusion.
    – RomaH
    Commented Jul 21, 2017 at 21:19
the EPA's restrictions on particulate matter are not supported by evidence

This isn't completely true, there is evidence showing particulate matter is harmful for humans. The bulk of this evidence is in the form of Epidemiology studies, looking at human health statistics and comparing to their exposure to PM.

The issues the author brings up is that he doesn't trust the EPA, but even if we ignore all the evidence they are responsible for we still find evidence by other organizations (and other countries) that PM may be harmful, which still justifies having it regulated. How strong or conclusive this evidence is and what a 'fair' level of PM that should be allowed in emissions is also debatable. But lucky for us this is set by government and we should stick to that, just like a speed limit.

To show other organizations have a different view there is this study. To show why the evidence may not be considered strong you can compare it to this study on smoking, which is now widely accepted as bad for health and is also regulated to some fair level. Comparing the relative risk you can see it is much more clear that smoking is bad for your health.

Another reason that the evidence might be thought of as weak is that the PM may be from a source that is also producing actual poisonous gasses that are completely responsible for the health effects. Comparing PM to smoking again, there is evidence (besides Epidemiology studies) to show smoking is bad for your health, cigarette smoke contains cancer causing compounds. The same is not proven for PM.

Another point is that 90 % of PM is not man made, so even if evidence that PM alone is unhealthy (which we can't test without gassing people), regulating emissions may not be an effective way of mitigating those health issues.

  • What is your basis for the assertion that 90% of PM is not man made? Does that take into account the population around various sources of PM generation? (example: a volcano exploding in the middle of the wilderness creates a lot of PM, but is unlikely to have significant effect on human health. Things like factories, automobiles, and power plants, however, involve at least some human adjacency by their nature)
    – Ben Barden
    Commented Sep 11, 2018 at 14:37
  • From Wikipedia "anthropogenic aerosols—those made by human activities—currently account for about 10 percent of the total mass of aerosols in our atmosphere"
    – daniel
    Commented Apr 13, 2019 at 12:13
  • We can't tell that PM alone is unhealthy without gassing people? Besides epidemiological studies, we can run animal studies. Cigarette smoke contains cancer causing compounds, found after we discovered that cigarette smoke causes cancer. And a lot of things cause cancer in the lab, but at the doses and exposures in real life, don't meaningfully add to the risk. That some compounds in cigarettes are known to cause cancer doesn't have any real impact on the question of whether smoking causes a significant risk of cancer, particularly not compared to the pile of evidence that it does.
    – prosfilaes
    Commented Jan 26, 2022 at 17:02

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