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Welcome to PSR's Environmental Health Policy Institute, where we ask questions -- then we ask the experts to answer them. Join us as physicians, health professionals, and environmental health experts share their ideas, inspiration, and analysis about toxic chemicals and environmental health policy.


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Even on a Clear Day, PM 2.5 Lurks

Posted on April 14, 2011

By Joanne L. Perron, MD FACOG

This essay is in response to: What is the most important achievement we've gained through air pollution management? What remains to be done to safeguard public health from air pollution?

Adults breathe at a resting rate of approximately 12 breaths per minute, thus obtaining 3000 gallons of air per day. Exercise, stress, pregnancy, and many medical problems will increase the rate and amount. Babies and kids have a substantially higher rate due to their faster metabolism and greater activity level. Some people have restricted lung capacity due to underlying medical problems and must make up by breathing faster. Some, such as seasoned athletes, singers, and yogis have a more expansive lung capacity and thus can obtain the necessary oxygen with slower rates. Oxygen is necessary for us to generate energy molecules from the food we eat and is 21% of the air we inhale. The brain especially requires oxygen to function normally. That is why we can’t live without oxygen for more than a few minutes. We have to breathe to live.

Since we are dependent on air for our very vitality, it is particularly vexing to me that even 40 years since the Clean Air Act was legislated, our air continues to be polluted with many unseen toxic substances that harm that same vitality, especially that of developing babies and children. It is well known that air pollution contributes to asthma, exacerbates underlying lung and heart problems and has strong links with cardiovascular disease and premature death. More recently it has been associated with diabetes and the development of Alzheimer’s disease. These are serious and costly medical conditions.

As an OB/GYN, what I find even more alarming is the emerging research that links air pollution or living near a major roadway to adverse birth outcomes, respiratory-related infant mortality, and most recently, autism. Advice on smoking and alcohol cessation, eating healthy, exercising regularly, avoiding excess weight are all part of a prenatal visit, but how does an obstetrician counsel pregnant women to avoid something as necessary as air? 

Air can be polluted by a myriad of chemicals. One of the most worrisome is a conglomerate called particulate matter or PM. Diesel combustion from motor vehicles and stationary sources is a major source of ambient air pollution including PM, especially in California. Metallic PM components such as Vanadium and Nickel are listed as carcinogens by the state of California (Prop 65 list). Like migrating birds, PM can travel several hundred miles from its origin and can get trapped in certain regional “cages” due to meteorological and geographical factors. For instance, PM from San Francisco or Sacramento affects air quality of California’s central valley, which is some of the worst air quality in the US.

Many magnitudes smaller than human hair, PM is classified into 3 different sizes: PM 10, PM 2.5, and ultrafine PM.

Because we often can’t see PM less than 2.5  in our immediate vicinity, we don’t realize it is there, somewhat like the infamous monkey: see no evil and breathe no evil. But, believe me, after being absorbed through the tiny air-blood exchange system in the lungs, PM has the potential to cause much harm to our health through complex pro-inflammatory pathways and a process called oxidative stress.

Over stimulation of inflammation pathways can lead to autoimmune disease such as lupus, arthritis, and cardiovascular disease. The body naturally forms certain levels of reactive oxygen species (ROS) as part of normal metabolism in mitochondria and to fight off infective invaders by white blood cells. Too much production of ROS, which occurs with exposure to toxic pollutants such as PM, can damage our DNA (oxidative stress) leading to damaged health and loss of vitality. A recent systematic review of the links between air pollution and adverse birth outcomes reported that exposure to PM 2.5 was associated with low birth weight, preterm birth and small for gestational age births (Shah, et al. 2010). Starting off life with this scenario can lead to a multitude of problems across the lifespan, from learning disabilities to future metabolic disease and its sequelae.

We obtain anti-oxidants from a rich and varied diet of fruits and vegetables to keep the naturally occurring ROS in check. However, I suspect that even if Americans consumed the recommended 5 cups of fruits and vegetables per day, a significant amount of environmentally induced oxidative stress would go unchecked. Omega 3 fatty acids are anti-inflammatory, but given that many fish are tainted with mercury as well as many halogenated and thus persistent chemicals, it seems counterintuitive to expect that dietary choices alone can overcome inflammation from exposure to PM 2.5. In other words, although eating healthy is paramount to our health, we can’t rely on walnuts, eggplants, Brussels sprouts, and arugula to fight the battle against inflammation and oxidative stress alone.

Policymakers must take protection of the public’s health into consideration not only by setting pollution standards that protect our most vulnerable populations but also by rigorously enforcing the regulations despite objections of industry. In the instance of PM, this can only be done after appropriate PM measurement and speciation of PM in the communities most affected, even if the initial monetary cost seems prohibitive. There would be billions of health care dollars saved if only a small portion of adverse birth outcomes were prevented by reductions in exposure to PM and other harmful pollutants.

Current air quality monitoring does not consistently measure PM at near roadway sites, the most likely to show the highest levels, but rather captures regional exposure. The majority of communities are situated near major transportation arteries and hubs. Many of those are low-income communities or communities of color, consequently there is no way to really know the extent or specifics of exposure to PM in these populations. Unfortunately, these same communities, which are often located in food deserts, also have reduced access to preventive care, factors influencing health outcomes due to PM and other air pollution exposures.

The US EPA has issued standards for levels of PM exposure, which are considered “safe,” and California has even more stringent levels; however, California has the dubious distinction of having the largest geographic non-compliance area.

Image courtesy US EPA.

Very soon, the US EPA will be revising the National Ambient Air Quality standards for PM 2.5 and so a prospect exists to shape and influence future policy in this regard. I have had the opportunity to work on this project with an amazing group of women from Central California in a yearlong fellowship called “Reach the Decision Makers.” Conceived and managed by the Program on Reproductive Health and the Environment at UC, San Francisco, the program envisions training public health professionals to collaborate and become effective advocates for and communicators of specific policy projects related to reproductive environmental health.

Our group recently met with US EPA officials in Region IX in California and at Research Triangle Park, North Carolina, and made the following policy recommendations:

  • Monitors should be placed near roadways that can speciate the pollutant mixture.
  • Such monitors will provide critical data for future epidemiologic studies that can answer questions about the cumulative health effects of PM2.5 in communities that live, work, and play near our roadways.
  • These monitors coupled with modeling techniques will inform appropriate changes that can improve public health of everyone including our most vulnerable populations. 
  • The precedent set by the revision of the nitrogen dioxide rule of the Clean Air Act can serve as a model for PM given they are both traffic-related pollutants.
  • We recommend that the US EPA estimate the monetization of adverse birth outcomes to include the lasting effects throughout life course. These additional costs attributable to air pollution can then be compared to those of monitoring and reducing air pollution.

Our efforts can be supported by the input of all who value the fundamental right to air devoid of harmful substances. Please considering signing on to this petition or writing to the US EPA when public commentary opens up.

Maybe our theme song should be “On a Clear Day You Can Breathe Forever.”


ronald moss M.D. said ..

And a major cause of asthma exacerbations.

April 14, 2011

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