Sustainability: Phoenix Metro Air Pollution Study

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An Arizona State University professor has done an in-depth analysis of air pollution in the Phoenix area that is longer than most studies of its kind and also looks at the size of particulate pollution. Professor Tom Cahill says that’s important because smaller particles can make it deep into our lungs. Cahill will discuss his report.

Ted Simons: Good evening, and welcome to "Arizona Horizon." I'm Ted Simons.

Ted Simons: An ASU professor recently completed an in-depth analysis of air pollution in the Phoenix area. The study looks specifically at the size and number of particulates in the valley's air. Here to talk about his report is ASU professor Tom Cahill -- it's good to have you here. This is always interesting with air pollution, but let's start by defining air pollution.

Tom Cahill: Well, nowadays people like to use the term air quality. The reason being is not all the particulate matter in the atmosphere is man-made. Dust,spores,pollen. They're all natural. So people like to refer to it as air quality to incorporate both the natural and the man made. But basically air pollution can be divide in addition two categories. One are gasses, like ozone, carbon monoxide, the other is particulate matter, basically the solid material in the atmosphere. Dust, soot, pollen, spores, etc.

Ted Simons: What do we know about particulate pollution?

Tom Cahill: Well, most often people measure just particulate matter. If you watch the evening news and you see the forecast of health warning, and in winter it's due to particulates. Particulates come from many sources. They can come from vehicles, from wood-fire power plants, from fireplaces, from power plants, they can be natural, they can be dust, pollen, they can be spores.

Ted Simons: And again, your study looked at the size of these particulates and there is a difference, because those bigger ones may seem worse, but they're not worse, are they?

Tom Cahill: Well, the bigger ones tend to be more innocuous in terms of chemistry. They tend to be large particles. They'll be dust, they're going to be pollen, they're going to be spores. Most of these are natural. We don't have to worry too much about them. It's the smaller particles which actually have the more toxic origins. Mostly combustion -- Vehicle, welding, fireplace.

Ted Simons: More toxic because they get into the bloodstream?

Tom Cahill: For two reasons. One, your nose and upper bronchial tracts have mechanisms to screen out big particles. There are defenses against it. The smaller particles can defense those mechanisms, hence they can get deeper into the lung and your body does not have as many defense mechanisms deep in your lung. After all, the whole idea of the lung is to get efficient exchange of gasses across into the bloodstream. So the small particles can more easily get absorbed by the body and circulate within the body.

Ted Simons: So it sounds to me like you see the haboob and you see these massive dust storms and think oh, bad stuff is coming. But much of that is larger particulate as opposed to maybe the stuff you don't see with exhaust.

Tom Cahill: Well, the larger particulate from the haboobs are basically dirt, dust being blown around. The advantage of the dust, is that it settles quickly. You may have really bad air quality for a couple hours, and then it settles down. So actually in terms of the long-term average, those storms are impressive, but don't contribute much to the long-term particulate load. What's more worrisome is the winter time aerosols. One, they last in the atmosphere for days or weeks, and two, they are the ones that get into your lung more readily. The big dust gets screened out by your nose.

Ted Simons: When you say days or weeks, you're talking those inversions.

Tom Cahill: Exactly. The problem with the inversion is it traps all the air pollution we generate near ground level. By having a smaller volume of air we put the same pollution into it, it stagnates. It just sit there's and builds up. In the summer, we have the sun warming the ground, the air aloft and takes pollution witness. Therefore the pollution is swept out very efficiently in the summer, whereas in the winter it's trapped in us. Or trapped at ground level with us.

Ted Simons: Yeah. And we wind up breathing it in. Your study in general, tell us, what you were looking at looking for and what you found.

Tom Cahill: What we were looking for was the following -- Most people that measure particulate matter measure one value. It's the amount of mass in the air at a particular time. They boat bother to differentiate based on size, other than micron parts. And they don't dot chemistry out. There's only really one site in all Phoenix that EPA runs that does any chemical -- Looks what the particulate matter is made of. The reason being, it's important to know what the particulate matter is made of. Don't tell me a gram of sand and dust is as toxic as diesel soot. So you really need to look at what the particulate matter is made of, in addition to its size in order to understand how hazardous it is. So what we did is focused on learning both the composition and the size fractions of the aerosols present. So we did chemical speciation for each of nine size fractions, for the coarse dust stages to the very fine ultrafine stages. And that way we can separate the biological dust and pollen mass, which is harmless, away from the much more toxic soot.

Ted Simons: And when you did that separation, were there any surprises out there? First, where did you -- Where were the locations for these things?

Tom Cahill: For simplicity we set up on the ASU west campus at Thunderbird and rd, and so we're in a pretty representative suburban area in Phoenix. We're not downtown, we're not out in the very fringe. So we're really a good representative air quality sample. So what we found basically is what you'd expect. That the winter time aerosols tend to be smaller and combustion-related. Everyone loves to blame wood smoke. In fact we have no-burn days specifically designed to limit emissions. The only problem S. the inversion traps all pollutants. So we have tracers that show us which smoke is highest in the winter, but also vehicle exhaustion is highest in the winter. But wait, vehicles -- Source strength is not changing, the same number of cars is roughly on the road as winter and summer. That's the effect of the inversion.

Ted Simons: But it still makes sense, do you think, to have these non-burning days for wood? Yes, they're different, and -- But they're all getting trapped. You want less trap, don't you?

Tom Cahill: The no-burn days are a good idea. But they're not necessarily the only solution out there. We need to slowly work on the additional sources that are starting to be called the off-road sources. Things like lawn equipment, barbecues that may also add to additional pollution to the atmosphere. But, yes, no-burn days are a good idea. The only problem is enforcement.

Ted Simons: No kidding. So anything surprise you, anything you -- When the study was done? This is a comprehensive study. Anything you went, I didn't expect that.

Tom Cahill: The main thing is how little of an effect the haboob had. I expected that there would be a lot of soil contaminants, basically microbes, spores, detritus, and they'd have a strong organic signature. A bunch of fatty acides in biological materials, sugars. I expected them to be higher. In retrospect it makes sense because there isn't that much organic material in soil to begin with in the desert. Desert soils are low in organic material. So I expected more, but it was not a factor.

Ted Simons: Last question here -- What do we take from this study, what should we do with the information that you studied?

Tom Cahill: Well, let me take your question and rephrase it. What can you do about air quality? Basically the single best suggestion I have for you is get a good filter for your air conditioning, heating system. And the reason being is they can filter out a lot of the fine particulate matter. In particular, they can get rid of the fine particulate matter that can enter your homes. Everyone thinks of the haboobs, you go indoors and you're protected. Yes, they're coarse aerosol and they're short-lived, but in winter, they get indoors. Once again, how much time do you spend outdoors? We spend most of our life indoors. Whether it's home or work. So by cleaning up the air where we're breathing it makes the most sense.

Ted Simons: Lastly, for those of us who jog in the mornings, do exercise outside in the mornings, should you wait a while in the winter? Maybe get past that morning and get to where the sunburns some of that off?

Tom Cahill: The sun doesn't burn it off. It may lift it. When the sun warms the ground, the warm air starts to rise and will lift the inversion. I'm not sure how much of a difference it would make. You might have to wait a few hours, which cuts into work.

Ted Simons: You get -- Very interesting stuff. Thanks for joining us. We appreciate it.

Tom Cahill: Thank you.

Tom Cahill:Professor, Arizona State University;

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