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.

Humid continental climate is found in the interior of continents between the 30 and 60 degrees latitude, but usually above the 40 degree line.   40 degrees north of the equator means less direct sunlight and therefore less warmth.   this climate is mainly found in the northern hemisphere since there are no major landmasses in the southern hemisphere.  if you live in northern indiana, you know all about humid continental because that is the climate type you have!