Question

Total columnar ozone in the atmosphere is measured in Dobson units. One Dobson unit corresponds to ______

• A. \(\frac{1}{10}\) of mm
• B. \(\frac{1}{100}\) of mm
• C. \(\frac{1}{1000}\) of mm
• D. \(\frac{1}{100}\) of cm

Hint:

1 DU is a 0.01 mm layer of pure ozone at standard conditions.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
A Dobson unit measures how thick the ozone layer would be if all the ozone in a column of air were pressed into a layer at standard temperature and pressure.

Step 2: Key fact:
One Dobson unit equals a layer 0.01 mm thick. So 1 DU = \(\frac{1}{100}\) mm. A normal ozone column of about 300 DU would be 3 mm thick.

Step 3: Check option 1:
\(\frac{1}{10}\) mm is 0.1 mm. That is 10 times too large. Wrong.

Step 4: Check option 2:
\(\frac{1}{100}\) mm is 0.01 mm. This matches the definition. Correct.

Step 5: Check option 3:
\(\frac{1}{1000}\) mm is 0.001 mm. That is 10 times too small. Wrong.

Step 6: Check option 4:
\(\frac{1}{100}\) cm is 0.01 cm, which is 0.1 mm. That is again 10 times too large. Wrong.

Final Answer:
One Dobson unit is \(\frac{1}{100}\) mm.\[\boxed{2}\]