by Susan Hellauer
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The 13th of June was just another bright, broiling 90-plus-degree day—one of many we’ll endure this summer. Rockland County officials passed along an Air Quality Health Advisory for the entire New York metro area, originally issued for June 13 by the NY State Department of Environmental Conservation (NYS DEC).
The pollutant of concern for the Air Quality Health Advisory is ozone.
The Rockland County Department of Health recommends that residents limit strenuous outdoor physical activity, such as jogging, ball-playing and running during the afternoon and early evening hours when ozone levels are highest. Although all individuals may be affected by ozone exposure, some people may be more sensitive than others. Young children, the elderly, people with pre-existing lung disease such as asthma and people with pre-existing heart disease or high blood pressure may be more seriously affected during an ozone advisory. It is very important that these individuals reduce their exposure during an advisory and limit all outdoor exercise and physical exertion when ozone levels are elevated. It is helpful to remain in an air-conditioned location.
Good ozone? Bad ozone?
But, wait a minute. Isn’t the ozone layer the stratospheric sunscreen that protects us all from frying to a crisp in the sun’s harmful rays? Don’t we worry about “holes” in it that put us at risk? This advisory makes it sound like ozone is a bad guy, not a good guy. What gives?
To get the lowdown on ozone, we called Dr. Benjamin Bostick, professor of environmental geochemistry at the Lamont-Doherty Earth Observatory in Palisades, NY. He cleared up the smog around this two-faced molecule.
What, exactly, is ozone?
Ozone (O3) is a form of oxygen with an extra oxygen atom—one more than normal oxygen (O2). This makes it more unstable and more chemically reactive than oxygen. It can be useful, but it can also be toxic.
I thought ozone was our friend—that stratospheric layer 6 miles+ above the earth that protects us from the sun. Is it the same ozone that these advisories warn us about?
Up there in the stratosphere, ozone acts like earth’s sunscreen. Because it’s unstable, it breaks down and re-forms by absorbing light, thus protecting us from those nasty ultraviolet (UV) rays.
Down here in the troposphere, where we live, ground-level ozone is a contaminant, causing oxidation. That means it can kill stuff, which makes it good for drinking water treatment, for instance. But even a low concentration of ozone in our air, which is reasonably common, can have a number of adverse health effects.
So, does the ozone from up there come down here on hot days? Is that the problem? If not, where does it come from?
The stratosphere (6-30 miles up) is very cold and not dense, while our troposphere (from earth to the stratosphere) is dense and warm. There’s very little transfer between these two layers.
Down here, we make our own ozone, especially on long, hot, sunny days. The main culprit is tailpipe emissions from fossil-fuel vehicles. The nitrogen oxides (NOx) in these emissions are chemically converted, with heat, sunlight and atmospheric oxygen, into ozone, a harmful component of photochemical smog. By late afternoon, ground-level ozone concentrations have already been rising for hours, which is why advisories usually warn us most strongly about these times.
Ozone degrades over time, and generation falls off overnight. With the morning rush hour the cycle starts again.
I read somewhere that emissions from distant sources can cause this bad ozone? What are they talking about?
We have to remember that tropospheric ozone is a secondary contaminant, formed photochemically after nitrogen oxides are emitted from tailpipes on a warm, sunny day. And ozone doesn’t necessarily stay in one place.
In bowl-like landscapes, like Los Angeles or Phoenix, a cloud of brownish-yellow ozone smog will stay put. In our area, which is not a bowl, we share our morning rush-hour ozone with swaths of Connecticut and Massachusetts, where it endangers people, plants and agriculture.
Most ground-level ozone is caused by tailpipe emissions. Power plants, especially those that burn cleaner natural gas, contribute less to ozone generation than tailpipes.
So, should I wear a mask when I go out? How does this ozone affect me adversely? What could happen?
A mask won’t help with ozone. Statistically rare events are more likely to happen on “ozone alert” days to susceptible people, whose problems can be exacerbated (see box).
What can we, as individuals and all together, do about ground-level ozone pollution?
Limiting NOx tailpipe emissions is the big thing. We need low-nitrogen fuels, or no fossil fuels at all. It’s a difficult problem to address here, where we have a big concentration of cars and of miles driven and not enough public transportation.
The US Environmental Protection Agency tells us that ground-level ozone exposure can:
- Make it more difficult to breathe deeply and vigorously.
- Cause shortness of breath, and pain when taking a deep breath.
- Cause coughing and sore or scratchy throat.
- Inflame and damage the airways.
- Aggravate lung diseases such as asthma, emphysema, and chronic bronchitis.
- Increase the frequency of asthma attacks.
- Make the lungs more susceptible to infection.
- Continue to damage the lungs even when the symptoms have disappeared.
- Cause chronic obstructive pulmonary disease (COPD).
Ozone an also damage plants, trees and crops.
- NYS DEC Daily Air Quality Index (AQI) for New York State
- NYS DEC Ozone Fact Sheet and Ozone page
- NYS DEC Ozone Questions and Answers
- “Vehicles, Air Pollution and Human Health,” Union of Concerned Scientists
- NASA Earth Observatory: “The Ozone We Breathe”
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