Anyone driving west on Interstate 10 from the east San Bernardino Valley this morning likely saw a thick, yellow-brown wall of air pollution lying ahead. It’s not an uncommon sight, and it’s often accompanied by a distinctive, acrid smell that can make people think twice about taking a deep breath.

Sort of dispels the expression “morning fresh.”

So what is that stuff, exactly? Sam Atwood, longtime spokesman for the South Coast Air Quality Management District, said the likely culprit is PM 2.5, microscopic particles that combine to form one of the more troublesome forms of air pollution.

via BROWN AIR: Morning pollution a pall in SB Valley : Environment.

Fo local air quality info: South Coast Air Quality Management District, AQMD

What does PM stand for? Read here.