To celebrate the end of ozone season and to present information on our future plans, STA in NC will be holding a members’ potluck at Jacobson Ranch, just north of Nevada City, on Thursday, October 8, from 6 to 8 pm.

After a potluck dinner, our members will tell you about our 2009 activities, the status of our Grass Valley and Nevada City monitors, what we learned over the past ozone season, and what we’re planning for the future. The band Silver Wings will entertain us during dinner and after the presentations.

Please bring some food or drinks to share, your questions and curiosity, and suggestions for future activities. If you’ve been looking for a way to become more involved with STA in NC, this is the meeting to attend. We hope to see you there!

Directions to Jacobson’s Ranch: From Highway 49, take Cement Hill road 1.5 miles up the hill to 11153 Cement Hill Rd (on the left). After pulling into the driveway, there is a parking area to the left.

De-mystifying the Air Quality Index

It’s a hot summer’s night. Sleep is impossible. To make matters worse, mosquitoes have found a hole in the screen.

If only, say, two mosquitoes get through the screen, the situation might not be too bad. Our “mosquito radar” can track two mosquitoes. Should one light, you’d notice and slap her before she could drink.

Should four mosquitoes get through the hole, human reflexes could probably still handle the situation.

Six mosquitoes, though, might be pushing things, and eight would definitely be a challenge. Distracted by a mosquito exploring your arm, you fail to notice the one dining on your leg.

Many toxins seem to act in a similar way: The body’s defenses – detox and repair systems – can deal with small quantities of poison, but larger quantities overwhelm us.

The ozone AQI – or air quality index – assumes ozone works this way. A certain amount of ozone in the air is deemed not to be harmful; beyond that amount, it becomes dangerous.

Ozone absorbs ultraviolet (UV) radiation.

That is why ozone in the stratosphere, more than 20 miles over our heads, is “good ozone:” It absorbs solar radiation that would otherwise damage DNA and cause cancer.

To measure ozone, instruments shine UV through the air, and measure how much is absorbed. The more absorption, the more ozone there is.

Under federal air regulations, if there are no more than 59 molecules of ozone in a billion molecules of air, air quality is considered “good:” It should have no impact on health.

Regulators feel we can deal with 59 “mosquitoes” in that much air.

Sixty molecules of ozone in a billion molecules of air – 60 parts per billion, 60 ppb – is a “breakpoint,” where air quality is no longer described as good, but as “moderate.” When the air has this much ozone in it, says the EPA, “unusually sensitive people should consider limiting prolonged outdoor exertion.” But for most people, the agency feels levels up to 75 ppb will not have adverse health effects.

Seventy-six ppb is the next breakpoint. Air with 76 molecules of ozone per billion molecules of air (76 ppb) is deemed unhealthy, not for everyone, but for people who are especially sensitive: Asthmatics; people with lung disease; and the elderly.

It’s also unhealthy for anyone exercising. That’s because breathing deeply, we pull more air – and more ozone – into our lungs.

Reporting air quality in parts-per-billion can be cumbersome, so air agencies convert these numbers to “rounder” ones. If there are 59 molecules of ozone for each billion molecules of air, the AQI is reported as 50 – the very upper edge of what’s considered “good.”

If there are 75 ppb, the AQI is 100 – the very upper edge of “moderate.”

A reading between 60 and 75 translates to an AQI between 50 and 100.

And so on.

Those who consider air pollution regulations onerous point out that these are awfully tiny amounts of ozone Ð that 76 ppb (which translates to an AQI of 101, the breakpoint where the air is deemed harmful to sensitive groups) is equivalent to making a martini with an ounce of vermouth in something over a hundred-thousand gallons of gin.

True, but irrelevant. If anything, it demonstrates ozone’s potency as a toxin.

The AQI embodies a couple of assumptions: First, that there is a natural baseline – a level of ozone that would exist in the air even if humanity were driving no cars or trucks, generating no energy, fertilizing no farms, clearing no forests. Second, that this “natural background” level causes no adverse health effects.

Over the years, the AQI calculation has been repeatedly revised to make it more conservative, reflecting accumulating evidence that natural background levels are lower than had been presumed, and ozone more harmful. The most recent revision was made this past March; some say it’s already due for another.

His statement follows:

OZONE: Presentation to Nevada City City Council

The ordinary, garden-variety oxygen we breathe is a very simple molecule, just two oxygen atoms glued together. But 25 miles or so over our heads, there’s another type of oxygen molecule, an oddball molecule made of three oxygen atoms glued together. Triatomic oxygen is ozone, and it’s good stuff: it intercepts ultraviolet radiation from the sun that would otherwise turn us to toast.

Twenty-five miles up: good ozone. Unfortunately, there’s ozone lurking here at the surface, too.

Ozone is very good at stealing the electrons that glue molecules together – steal their electrons, and molecules fall apart. When rubber molecules fall apart, your tires crack; when molecules in your body fall apart, you grow old.

Cars and trucks and power plants don’t put ozone into the air, but they pump out the ingredients – the “ozone precursors” – that, cooked in the sun, make ozone.

We all learned in kindergarten that you could make one color by mixing two others: blue and yellow make green.

You can do the same trick backwards: Starting with white light, you can make a color by subtracting other colors from it.

Look out over the Sacramento Valley as you’re racing down I-80 and there’s often a red-brown haze floating over the city. The valley’s air is rich in molecules of nitrogen dioxide – molecules that suck the blue and violet and ultraviolet out of white light – which makes it look red.

The energy of that missing light must go somewhere … it makes the molecules of nitrogen dioxide fall apart … and from those broken molecules come the atoms needed to turn ordinary oxygen into ozone.

But only while the sun is shining. When the sun goes down, ozone production stops. When the sun goes down, the ozone level in the valley begins to fall. Some of the same molecules that go into making ozone during the day go into breaking ozone molecules at night, when there’s no blue or violet to absorb.

Here in the foothills, we don’t have nearly as much traffic as they have in the valley, so we don’t produce nearly as much of the ozone precursors to break apart our ozone at night. When the sun goes down, foothill ozone levels may go down, but they don’t go as low as they do in the valley.

It’s counterintuitive, but, 24/7, we in the foothills have a worse ozone problem than do the urban areas – the Bay Area and Sacramento – that export their pollution to us.

We in the foothills are used to thinking of ourselves as being upslope from the valley … upstream from the cities … but we’re also downwind … and that’s why we have a problem with our air.

Save-The-Air in Nevada County has begun monitoring ozone levels around the county, to complement the work being done by the local air management district. We’re also comparing the air indoors and out, because, when ozone levels climb, we’re warned to avoid exercise and to stay indoors –to “shelter in place.”

Ozone reacts with all sorts of chemicals that float in the air of our homes. The good news is that this brings the ozone level down. The bad news is that some of the products of those reactions are more toxic than ozone itself.

Current plans call for Sacramento to clean up it air by 2013 … but new plans are in the works, with a new deadline: 2024,

That’s a long time for us to hold our breath.