The atmopsheric quality at time t—denoted A(t)—is measured by the number of pollutant units residing in the airshed at that time. These units are emitted from pollutant sources one unit at a time with...

The atmopsheric quality at time t—denoted A(t)—is measured by the number of pollutant units residing in the airshed at that time. These units are emitted from pollutant sources one unit at a time with rate a. The emission process can be assumed to be poisson. Each unit thus emitted gets diffused in an average time of length ß. Also assume that the diffusion times are exponential random variables which are independent and identically distributed. Obtain the mean and variance of A(t) as t ? 8.