The velocity of wind moving past a constant emission source changes from 4 to 2 m/sec.

What is the relative quantitative effect of this change of wind velocity on the pollutant concentration downwind (e. g., inside a city) ? Assume the pollutant concentration upwind is negligible compared to the pollutant concentration downwind.

Concentrations will decrease to one-quarter of their initial value.

Explanation:

The relative effects of the changes in the velocity of the wind on the pollutant concentration will decrease in one-quarter of the initial values. When assuming the pollutant concentration is negligible upwind to the content downwards. The concentration will be the emission rate gets reduced to the one-quarter of the initial value and then by the pollution concentration will be reduced with downwind.