In this paper, Advection - diffusion equation (ADE) has been solved in two dimensions using the separation technique to obtain the crosswind integrated ground concentration considering vertical eddy diffusivity and mean wind speed depend on power law and time. We compared between estimated concentrations and observed which conducted in the Northern part of Copenhagen, Denmark of sulfur hexafluoride (SF6) which released from a tower at a height of 115m without buoyancy. Comparison between estimated and observed crosswind integrated of pollutant concentration per emission rate, there are some present data which are agreement with observed data (one to one), others lie inside a factor of two and four.