Dust Storms and Air Quality!

Adding to nature’s arsenal of impactful weather are dust storms! Residents of the Sonoran and Mojave Deserts of the southwestern U.S. are very familiar with blowing dust occurrences every year. Blowing dust is not restricted to any particular season as long as dry and loose soils combine with strong winds . However, the summer North American Monsoon certainly stands out as a prime time to observe this dangerous, yet often photogenic, natural phenomenon!

The monsoon onset is a particularly vulnerable time for society living in this part of the world as parched desert soils baking under the climatologically driest and hottest month of June become susceptible to gusty thunderstorm outflow winds, typically by early July. Until beneficial rains stabilize vast tracts of exposed desert landscape, blowing dust remains a forecasting concern. It’s no wonder that the National Weather Service has a distinct “Dust Storm Warning” category with criteria of “localized blowing dust reducing visibilities to one quarter mile or less is occurring or imminent”.

 
Unfortunately, large portions of the deserts may only receive limited or delayed summer precipitation to help suppress the amount of dust lofted during ongoing thunderstorm high wind events impacting the region throughout the summer rainy season. Additionally, should rain fall and replenish topsoil moisture, the suppressing effect can be short-lived as strong atmospheric moisture demand throughout the summer facilitated by triple digit heat quickly evaporates moisture from prior rains.

This ebb and flow in blowing dust risk needs constant assessment from operational meteorologists, especially those focusing on air quality! Excessive dust is not only a visibility driving hazard, but also a health concern with direct exposure. Besides wind strength and altitude penetration, dust storms can also be “measured” by its concentration of particulate matter, specifically what the U.S Environmental Protection Agency (U.S. EPA) call “coarse” and “fine” particle pollution (i.e., “PM10” and “PM2.5”, respectively). 

To get a sense of scale, PM10 is the larger variety of the two classes of federally monitored airborne particulates and still are smaller than the width of a human hair. Potential health concerns arise due to tiny airborne particles able to enter deep into the lungs and cardiovascular system after inhalation. The U.S. EPA 24-hour health standard is 150 micrograms per cubic centimeter (ug/m3) for PM10 and 35 ug/m3 for PM2.5. It is not unprecedented for short term excessive coarse and fine dust concentrations associated with powerful dust storms to exceed both health standards for the day in a matter of hours or less! Best to stay inside and wait out an approaching dust storm.

Lingering dust after a passing dust wall is a common issue, so continuing to limit outdoor exposure during hazy conditions is beneficial. Often times daytime atmospheric mixing by the next day, especially during the hot summer, is enough to quickly lift haze off the ground and begin dispersing particles to improve local air quality and visibility. Although not always environmentally possible, the best outcome for air quality is the initial dust laden thunderstorm outflow boundary is able to trigger new thunderstorms along and behind the passing dust wall with wetting rains to remove lofted dust.

Learning Resources:

U.S EPA PM10 and PM2.5

Photo Credit: Jonny William Malloy