Optional Assignment #1 Answers

Answers to Optional Assignment #1

Photosynthesis removes CO₂ from the air. Just as atmospheric CO₂ concentration peaks during the late winter - early spring when plants are dead or dormant and photosynthesis is at a minimum, CO₂ peaks at night when photosynthesis activity decreases because there isn't any sunlight.

The easiest way to answer this question might be to remember that pressure decreases most rapidly with increasing altitude in dense air. Pressure might decrease 150 mb in the right column of air when you move from the 900 mb level up to Point B. There would be a smaller decrease in the lower density air in the right column; pressure might only drop 100 mb. The pressure at Point A is greater than the pressure at Point B.

When you move downward from the 900 mb level to the ground pressure will increase. It will increase by 150 mb in the right column and by 100 mb in the left column. The pressure at Point C is less than the pressure at Point D.

There is nothing special about the 150 mb and 100 mb values used above. You could use different values. The important point is that whatever value you use for the dense air in the right column must be greater than the value used for the low density air in the left column.

The figure above shows what would happen during the night when warm air is in contact with cold ground. At the start of the night the entire air mass is warm (left figure). By midnight (middle figure) the bottom layer of air, in contact with the ground will cool. By the end of the night the layer in contact with the ground is cold, the middle layer is cool, and the top layer is warm. Temperature is increasing with increasing altitude, a temperature inversion has formed during the night.

In Question #9, we really can't see most gases. Pollution sometimes does produce visible haze, but that is usually because some of the gaseous constituents of the smog has condensed to form small particles or drops that scatter sunlight (just like the water droplets in a cloud or in fog). A similar situation arises in Question #16.

Question #10 is demonstration of an important principle that we will come back to when we get into Chapter 2. We will find that hot air floats because it has lower density than the air around it. Cold air sinks because it has higher density than the air around it.

There is 1 more unit being added to the air in Question #14 than is being removed. That will cause the atmospheric CO₂ concentration to slowly increase with time.

10% of 1000 mb is 100 mb.
If 1000 mb decreases by 10%, the pressure will drop to (1000 mb - 100 mb) = 900 mb.
10% of 30 inches of mercury (in. Hg) is 3 in. Hg.
So the barometer reading will drop from 30 in. Hg to (30 in. Hg - 3 in. Hg) = 27 in. Hg.