Answer
The histogram below shows the comparison of the two distributions.
The number of cities remain unchanged for the 15-19 and 40-49 $g/m^3$ ranges.
In the 25-39 $g/m^3$ range, the number of cities now is less than that of 5 years ago.
And the number of cities now for the 10-14 $g/m^3$ region is more than that of 5 years ago.
