The problem is caused by what's called a temperature inversion.

A temperature inversion is pretty close to what it sounds.

He considered other possibilities, with a temperature inversion as the most likely cause.

Air quality is a concern, especially in winter when temperature inversions are common.

However, if there is a temperature inversion just above the mountain top, part of the air will not make it all the way down.

As goes the ozone layer, so go our temperature inversions.

And it's quite true that there's no vertical movement of the air in a temperature inversion.

This usually occurs during a temperature inversion, and lasts for a few days.

During temperature inversions, they reportedly exceed such levels by up to 10 times.

The sky is all overcast, so maybe it's a temperature inversion.

The number of days with temperature inversions varies between 200 and 220 annually.

It was held down by a temperature inversion and was moving slowly.

It's just possible that it could be some kind of off-beat temperature inversion.

There are also pronounced vertical differences due to the temperature inversion.

Due to the mountains to the south of the city, temperature inversions are common, occurring on about 200 days per year.

But overnight something changes and now this same temperature inversion causes only one or two targets.

During winter, temperature inversions are a common problem, causing air pollution in the valley.

This means that a temperature inversion occurs at night.

Temperature inversions are common, and affect people more in the summer, according to the Met Office.

When temperature inversions arise in winter, heavy ice fog often results.

The surface cooling results in a large temperature inversion at the top of the marine layer.

An Accuweather.com meteorologist said the smoke was trapped by a temperature inversion.

Each had experienced temperature inversion which had disappeared within 2 to 4 months.

A new condition has also been suggested by other parties to assess noise levels during temperature inversions.

For months a temperature inversion may cause 50 or 75 targets to appear on the radarscope.