August 29, 2008 The Pump Handle 1Comment

by revere, cross-posted at Effect Measure

I used to joke that the only plan the Bush administration had for dealing with air pollution was to put all the free radicals in jail. If you don’t know what a free radical is, it is a highly reactive form of a chemical, usually involving an unpaired electron. Radicals often are short lived intermediates in other reactions and can have half lives in the microseconds or less. In any event we’re talking seconds. It is free radicals that are formed by ionizing radiation. They quickly react with whatever chemicals are in their vicinity and if that chemical happens to be your genetic material, you can get the kind of programming error that leads to cancer.

Now a combustion chemist is reporting a new kind of free radical which he calls a “persistent free radical,” almost a chemical oxymoron:

Most atmospheric free radicals exist for less than a second. What’s different and distressing about the substances Dellinger found, he said, is that they persist.The process begins when combustion in an industrial smokestack, automotive tailpipe or even a household chimney releases fine particles of unburned material, such as soot.

As the gases begin to cool, altered versions of chemicals in the exhaust – the persistent free radicals – form and attach themselves to the soot particles.

A substance’s persistent free radicals may be more toxic than the substance itself, [H. Barry Dellinger, Dellinger, Patrick F. Taylor Chair of Environmental Chemistry at Louisiana State University] said.

Bill Suk, acting deputy director of the National Institute of Environmental Health Sciences, said the research was “significant” because “it takes the monitoring and the exposure of products of incomplete combustion to yet another level of potential impact on people’s health.”

Whether it actually affects people’s health, however, remains unknown, he said. (Philadelphia Inquirer)


In recent years air pollution epidemiologists have shown that levels of fine particles are strongly related to daily morbidity and mortality. But measurement of particulates in the air is related only to their size (technically not their physical size but the size of standard particles that have the same aerodynamic behavior). They can be made of anything: heavy metals, sand, vegetable fiber, whatever. But clearly the chemical composition makes a biological difference. If some of these particles are actually free radicals, they are even more significant.

This was a news report of a paper given at the American Chemical Society’s annual meeting, so I’m not sure what allows these particles to persist in this highly reactive form. There is so much science news these days that separating the wheat from the chaff is becoming increasingly difficult. This work seems to have gotten the attention of the number two person, Bill Suk, at NIH’s main institute for research into the basic science of environmental health.

We breathe about 20 cubic meters of air a day, i.e., the volume of air in a cube 20 2.7 meters on a side. That’s a lot of air. Trying to figure out exactly what are the harmful agents in the complicated physical and chemical mixtures in the modern urban air shed is a daunting task.

If this is indeed a new, general class of pollutant it is a significant finding. Once there is a way to measure it accurately, some good epidemiology is called for. We know how to do these epidemiological studies using sized particulate measurements. They are expensive and time consuming but have revealed extremely valuable information. If we can sharpen the exposure assessments by better characterizing the active components in fine particulates we may be able to make a qualitative advance in our understanding of the health effects of air pollution.

We’ll have to see.

One thought on “A new class of air pollutant?

  1. All air pollution is not created equal. Scientists at UC San Diego and other institutions have found that smoke from agricultural and cooking fires, plus industrial waste burning, clog the air of Mexico City — and very likely other global megacities — with tiny particals called aerosols, which are particularly harmful to human health. So, it’s not just vehicle and industrial emissions that are killing us and creating climate change.

    To learn more about this, check out

    Full disclosure: I’m a communications guy at UC San Diego, but this is still a really important story.

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