AUSTIN (KXAN) — After a foggy start to the day Sunday, the sun broke through mixing out the low cloud cover. But many have noticed the brown haze lingering over the city. The reason? A temperature inversion trapping air pollution (dust, pollutants, ground-ozone, smoke, etc.)
Under normal circumstances, the air touching the ground is warmer than the air above. This is due to the fact that the sun’s radiation directly warms the ground. The air touching the warm ground is heated through conduction (energy transfer through direct contact). This allows for a warmer layer of air near the surface and a layer of cooler air above (temperature profile: air temperature decreases with height).
IN DEPTH: During a temperature inversion, the reverse occurs — colder air near the ground and warmer air above. This sets up a stable atmosphere as cold air is denser than warm air and resistant to mixing or motion. This lack of mixing allows air pollutants to get “trapped” underneath the layer of warm air… creating a brownish haze in the sky.
So what caused the temperature inversion today? The dense fog and low clouds this morning kept the ground cool while layers of the atmosphere above warmed up.
Eventually, with the dense fog eroding and more sunshine breaking through, the atmosphere’s normal mixing behavior got underway. (And with the arrival of a potent cold front early tomorrow morning, all of this haze will get blown southeast with strong north winds packed behind the front.)