A team of researchers has been studying meteorological and air quality data collected during the 189 dust storms we’ve experienced in Phoenix since 2010. Based on that analysis, they recently unveiled the "Phoenix Dust Scale," a ranking system to assess the severity of dust storms.
Dust storms are a familiar, yet intense, experience, especially if you’re in your car when they happen. But even if you’ve been through one before, you might not know exactly what’s going on. The Phoenix Dust Scale aims to change that.
Randy Cerveny is a professor of geographical sciences at Arizona State University and a co-author of an American Meteorological Society Bulletin announcing the Phoenix Dust Scale. Cerveny helped develop the scale and joined The Show to talk more about it.
Full conversation
SAM DINGMAN: Thank you for being here. Tell us why it was important to you and all the folks working on this project to develop this system.
RANDY CERVENY: Well, that’s an important point. We had over 13 different groups around the Valley that were interested in doing this. We had 25 meteorologists involved with this particular project from places like SRP, from the National Weather Service, from ASU, from the Maricopa County Flood Control District.
We all got together and we realized that there was a need, that nobody else has done this before, so we decided what would be the best way to do it. And this started out, believe it or not, as a COVID-19 project about five years ago, and we had lots of discussions on Zoom about how we could possibly do this.
One thing that we’re trying to do is to keep it simple. And we came up with a fairly straightforward index that is primarily based on dust concentration. So how much dust is actually in the air? From the Maricopa County Air Quality Department, we have a network of sensors around the Valley that monitor exactly how many particulates are in the air around us, and we use that as our primary ranking scheme to figure out how big a dust storm can be.
DINGMAN: So speaking of how big the dust storm is, let’s break down in a practical sense exactly what the scale is. Tell us what the classifications are.
CERVENY: Sure, we have actually a major classification, then we have subclassifications, but our major classification is based on a scale from one to five, where each number basically represents how many micrograms of particulates we have in the air. So a ranking of one, would basically be a storm that had at least 1,000 mcg per cubic meter. You get up to a Category 5, which is as big as our scale goes, and that means that you have a storm that has produced more than 5,000 mcg per cubic meter. Those are major, major storms.
The premier example that we have of that one, and many people remember this from bygone days, is back in 2011. We had a storm on July 5 that made international news. I was getting calls from around the world saying, did you survive this dust storm that came through? And that is actually a Category 5.
DINGMAN: OK, but you said there’s also some secondary classifications as well.
CERVENY: Right. Basically what we want to try to do is also figure out how big is the dust storm? How horizontally extensive is it, and what are the wind speeds associated with it? Those are a couple of our other subcategories. So, we have letters that go after each particular storm. So a Category 5 might also be a widespread, high wind event. And so on.
DINGMAN: Got it. And how quickly will we be able to apply a classification to a dust storm? As everybody listening to this probably knows, they often come up very suddenly.
CERVENY: Right. And they don’t actually last too long. That’s the other thing is that a dust storm usually goes through the Valley within a period of about a half an hour. What this scale is designed to do — and we applied it experimentally this summer — is to provide a post-event analysis.
So we can’t tell you though that the Category 5 storm is coming, but similar to like tornadoes, we’re going to go out the day after and actually check the instruments and then say, “Oh, this was a Category 5,” just like they don’t tell you that “Oh, it’s a Category 4 tornado that’s coming towards you.” They’ll tell you the next day. That’s the way we’re going to work it with this dust storm scale.
DINGMAN: Well, in that spirit, Randy, a lot of folks listening to this will probably recall a dust storm we had back in late August. You came on and spoke to us about this dust storm. It was very intense, but according to this scale, it would only have been a Category 2. So can you give us a sense of, like, for people who remember that particular dust storm, what would a Category 5 look and feel like?
CERVENY: Well, that’s the interesting thing is that our perceptions, the visibility is somewhat a personal type of measure that it’s really hard, depending on where you are in the Valley, to make a determination of how dense a dust storm is based off of your eyes. So that’s why we’re trying with this scale to come up with a solid number index.
And actually measuring the amount of particulates in the atmosphere is a much more quantitative, a much more realistic way to try to get at how big a dust storm is rather than just by saying, “Oh, the visibility was bad.”
So what happened with that particular storm that we had in August that many people remember — it was a very visually impressive storm. But the other thing that people may not recall is that moments after that dust wall came into the Valley, as soon as that haboob came into the Valley, it rained, and it knocked the dust down.
And part of the criteria that we have based on the sensors that we have is that we have to have a dust concentration existing for an hour. And it didn’t last that long to give us that high value.
DINGMAN: OK. Well, just about 30 seconds left here, Randy. In a paper that you and your co-authors published about this, you acknowledge that there are some limitations to a scale like this. You’re kind of reducing a lot of important information, but for you the benefits outweigh the shortcomings of a system like that, right?
CERVENY: Right. All of our different groups have different needs. We actually had a couple of TV meteorologists that were involved. Amber Sullins and Royal Norman were part of this, and they want to try to help people be able to anticipate what to do during dust storms.
We had people from the Arizona Department of Environmental Quality. They’re concerned with what we call exceptional events. When nature causes air quality to drop, they need to be able to prove that it was nature, not humans, that actually caused that particular thing. So a lot of our different groups had very specific ideas of what they needed.
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