Residents of Phoenix, Ariz., which is alreadyranked No. 3 in year-round air pollution, received another air quality shockwhen a massive dust storm slammed into the metropolitan region.

Even as residents were cleaning up after the storm, Maricopa County Air Quality Department officials were warning that additional storms in the coming days could kick up another round of dust, including fine particulate matter that causes health problems.

The massive dust storm, called a “haboob” (an Arabic word for wind), raised a mile-high, 100-mile long wall of dust and particles that swept over the city Tuesday. Haboobs only occur in Arizona and parts of Texas, in the Sahara Desert and in the Middle East. They are caused by high winds kicked up by colliding thunderstorms.

Pollution levels skyrocket during the storms. Air quality officials in Phoenix reported that particulate matter at one monitoring site reached 5,000 micrograms per cubic meter, well beyond federal safety limits.

You can see a time-lapse video of the Phoenix haboobhere.

The outdoor air in Phoenix remained visible dirty, with a brownish tinge, more than 24 hours after the storm. Local car washes were busy afterward, and the storm resulted in delayed and canceled flights at Phoenix’s Sky Harbor Airport.