Example 1: At a certain time, the concentration of  measured at a location near a power-plant (A) is 200 ppm (parts per million). The  concentration at ‘B', 1 km downstream, is measured to be 10 ppm. At this instance, the average wind velocity is 1 km/hr. The wind is blowing in the direction of the higher (A) to lower concentration (B). If a balloon-sensor floating with the wind records a decrease of 50 ppm per hour, as it flows past ‘B', determine the rate of increase of the concentration measured by a stationary observer at ‘B'. |
