Combustion from a fossil-fueled vehicle produces particulate matter with a very small diameter (<2.5 µm) at a rate of 2400 mg/hour while travelling at 100 km/hour. These particles are dispersed throughout a volume that extends 2 m on either side of the road and up to a height of 3 m. The road is 4 m wide. If the initial concentration was 1 µg/m3 , what is the concentration of PM2.5 in the 100 km stretch of roadway after this vehicle has passed through?

You may assume that this is the only vehicle that passes during the hour.