Air pollution control

AIR POLLUTION CONTROL

1.  When do maximum ground level concentrations of pollutants occur in mountain valleys? Why?

Maximum ground level concentrations occur a few hours after sunrise when inversion layers are broken up and brought to the ground.

2.  What is an urban plume? How is it formed?

An urban plume is the large mass of polluted air that moves downwind of a city. It is produced from emissions from both mobile and stationary sources.

3. What air quality problems are associated with long-range transport?

Long-range transport results in elevated pollutant concentrations hundreds to thousands of miles downwind. It increases background levels in areas subject to regulatory compliance with air quality standards.

4.  Generally, how long does it take for a long-lived pollutant to be uniformly mixed vertically in the troposphere? Horizontally throughout the troposphere?

In the first case it may take days; in the second case, approximately one year.

5.  By what mechanisms are pollutants transported into the stratosphere?

These include (1) a uniform rising motion across the tropical tropopause,

(2) in the middle latitudes, rising along surfaces of constant potential temperature that cross into the tropopause, and (3) in events known as tropopause folds.

6.  Characterize air circulation in the stratosphere.

Because of the strong thermal inversion present there is limited vertical mixing. However, significant horizontal movement occurs between equatorial and polar regions.

7. What factors affect the lifetime of pollutants in the atmosphere? Pollutant lifetime is primarily affected by the pollutants' chemical stability and processes that bring pollutants into contact with earth surfaces.

8. What is dry deposition? What factors contribute to increased deposition rates?

Dry deposition is the removal of pollutants from the atmosphere in the absence of precipitation. Deposition rates for gas-phase pollutants are affected by their reactivity with surfaces and solubility in water.