The dust storm that swept through the Valley on Monday night has been classified as a Category 5 on the PHX Dust Storm Scale — the highest possible rating. Unhealthy air continued to hang over Phoenix into Tuesday evening.
The scale, developed by an ASU-led team, measures the severity of dust storms in the region. Category 5 events are rare. Dr. Ryan Heintzman, a professor at ASU’s School of Geographical Sciences and Urban Planning, says this is only the fifth such storm in the past 15 years. “In the 15 years that we’ve been looking at these dust events, this is only the fifth time that we’ve seen a Category 5 storm,” he noted.
Heintzman explained that the rating system was originally created to identify high exposure to dust and particulate matter. Ratings run from one to five, based on how much dust is packed into the air. The particles themselves are roughly five times narrower than a strand of human hair. Exposure can add up quickly: an hour outside during a Category 1 event might mean inhaling about 250,000 pieces of dust. Category 5 is five times that amount, potentially over a million particles.
Certain groups face heightened danger, according to Dr. Frank LoVecchio, an ASU professor and emergency room physician. “People with lung disease, heart disease, the very young, the very old, or those who are immunosuppressed are the ones who get into trouble during this time,” LoVecchio said.
Meanwhile, ASU has rolled out a new dust storm dashboard that shows the storm’s category and how strongly it impacted specific locations across the Valley.