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Study finds declining PM2.5 levels continue to improve life expectancy in US

A new study led by researchers at Harvard School of Public Health (HSPH) has found an association between reductions in fine particulate matter (PM2.5) and improved life expectancy in 545 counties in the US from 2000 to 2007. It is the largest study to date to find beneficial effects to public health of continuing to reduce air pollution levels in the US.

The study appears in the journal Epidemiology.

Despite the fact that the US population as a whole is exposed to much lower levels of air pollution than 30 years ago—because of great strides made to reduce people’s exposure—it appears that further reductions in air pollution levels would continue to benefit public health.

—lead author Andrew Correia, a PhD candidate in the Department of Biostatistics at HSPH

The study looked at the effects on health of fine particulate matter, small particles of 2.5 micrometers or less in diameter—referred to as PM2.5. Numerous studies have shown associations between acute and chronic exposure to fine particle air pollution and cardiopulmonary disease and mortality. Studies have also shown that reductions in air pollution are associated with reductions in adverse health effects and improved life expectancy. Air pollution has been declining steadily in the US since 1980, but the rate has slowed in the years since 2000. The HSPH researchers wanted to know whether the relatively smaller decreases in PM2.5 levels since 2000 are still improving life expectancy.

Controlling for socioeconomic status, smoking prevalence, and demographic characteristics, the results showed that a decrease of 10 micrograms per cubic meter (10 μg/m3 ) in the concentration of PM2.5 during the period 2000 to 2007 was associated with an average increase in life expectancy of 0.35 years in 545 US counties.

The research expanded on a 2009 study published in the New England Journal of Medicine by some of the same authors (Pope, Ezzati, and Dockery) that found that reduced air pollution was associated with increased life expectancy in 211 urban counties. This new study looked at more recent data, more than two-and-a-half times as many counties, and included both rural and urban areas. The findings showed that there’s a stronger association between declining air pollution and increased life expectancy in more urban, densely populated areas than in rural areas. The results also suggested that reduced levels of air pollution may be more beneficial to women than to men.

As to why there was a stronger association between reductions in fine particulate matter and improvements in life expectancy in urban areas, the researchers speculated that the composition of the particulates there may be different from that in rural areas.

Since the 1970s, enactment of increasingly stringent air quality controls has led to improvements in ambient air quality in the United States at costs that the US Environmental Protection Agency has estimated as high as $25 billion per year. However, the extent to which more recent regulatory actions have benefited public health remains in question. This study provides strong and compelling evidence that continuing to reduce ambient levels of PM2.5 prolongs life.

—senior author Francesca Dominici, professor of biostatistics at HSPH

Other HSPH authors included Douglas Dockery, professor of environmental epidemiology and chair, Department of Environmental Health; and Yun Wang, senior research scientist, Department of Biostatistics.

Funding was provided by the U.S. Environmental Protection Agency (R-834894, RD-83479801), National Institutes of Health (ES019560 and ES012054), Harvard-NIEHS Center for Environmental Health (ES000002), NIEHS (T32ES007142), MRC Strategic Grant, and the Health Effects Institute.


  • Andrew W. Correia, C. Arden Pope III, Douglas W. Dockery, Yun Wang, Majid Ezzati, Francesca Dominici (2012) The Effect of Air Pollution Control on Life Expectancy in the United States: An Analysis of 545 US Counties for the Period 2000 to 2007. Poster.


Kit P


“Controlling for ..”

But not improvements in health care since before 2000. I wonder if that could result in a 127 days of increased life expectancy.

A second issue is:

“a decrease of 10 micrograms per cubic meter (10 μg/m3 ) ”

It would be nice to know if the decrease is from a 120 to 110 or 80-70. Like most health hazards there is a level where the curve becomes flat.

“Air pollution has been declining steadily in the US since 1980, but the rate has slowed in the years since 2000. ”

That is correct. Some places in China are at a level of 3000 but once you get to an average of 30 for natural background the rate of improvement will slow to zero.

Just once I would like these people to share good news instead of spinning as things are still bad so you need to pay us to do more studies.


And Europe is going "green" by reducing Co2, which has boiled down to diesel engines.

Good for the planet, bad for the people who live near the roads.


Kit P wrote:
"but once you get to an average of 30 for natural background the rate of improvement will slow to zero."

Natural background of 30? The EPA measures annual background PM2.5 concentration to be about 1 μg/m3 according to page 5 of

Kit P


Consider me better informed as I was using 30 as an example. The study you provided is one of the worst I have seen as far as being misleading. Figure 2 shows red for a range about 12 to 60. So the central valley of California looks the same as where I live now that almost always has an AQI for PM 2.5 in the good range.


Well said mahonj.

Unfortunately, the permanently frozen subsoil in the Arctic is melting down to 3+ meters in many places and will soon release huge amount of methane which is about 20X worse than CO2 by volume. It will probably have a snowball effect on climate change.

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