What cause a weather inversion with fog and smog on sunny days?

Question

My daughter and I noticed areas of fog and smog on an otherwise beautiful sunny day.The low lying areas were covered and it was difficult to drive in.We live on Vancouver Island.

Answer 1

From the clues you have provided, the inversion is mostly likely caused by a big strong high pressure ridge over the area. Strong high pressure is associated with the sinking of air aloft. This sinking the air is stronger than the air rising cause by day time heating of the lower atmosphere. In other words, the strong sinking motion of the air aloft is preventing the smoggy air from mixing high enough to get "carried away" by the upper flow. This stable environment will keep the fog and smog trapped until the inversion breaks.

Since you live on Vancouver Island, the shallow cold marine layer may also play a role in keeping the inversion longer. (The marine air will keep the low elevation cooler.) This will make it even more stable. Thus, the smog will likely cause the fog and smog to remain longer or until the next storm system arrives.

Answer 2

It is called a temperature inversion. Temperature usually falls as you rise through the troposphere. Sometimes the temperature will rise through a layer, this is a temperature inversion.

There are two types of inversion, the radiation inversion and the subsidence inversion.

The radiation inversion is caused by the ground losing heat overnight and cooling the air in contact with the ground. The air near the ground can cool to a temperature below that of the air above it. On clear nights when cool air collects in hollows, you can often feel the rise in temperature as you walk up a slope. Radiation inversions are very common.

Sunsidence inversions occur near the centre of high pressure systems. The air in a high is descending or subsiding. As it descends, it warms. It can warm until it is warmer than the air below it producing a temperture inversion. Over a few days, the inversion will get lower and lower. If a subsidence inversion overlies a radiation inversion, the air is very stable and pollutants are going nowhere. On these days the smog will be trapped over the city all day.

Radiation inversions break when the sun heats the ground which heats the air and brings the temperature change through the troposphere back to normal. When that happens, pollutants trapped below the inversion can disperse.