The time series of scalar concentration at a fixed point in space is modeled by a system of Eulerian stochastic equations for velocity and concentration coupled with a Lagrangian micromixing model. The interaction by exchange with the conditional mean (IECM) model is used in both the Eulerian and Lagrangian frameworks. The model is applied to the case of a line source scalar release in homogeneous turbulence. The calculated time series includes the effects of the two time scales intrinsic to concentration fluctuations, namely the large scale fluctuations due to meandering, and the small scale fluctuations due to relative dispersion. The intensity of concentration fluctuations, the cumulative distribution function of concentration, and time series of concentration are compared to experimental results. The velocity conditioned scalar probability density function are shown at several downstream distances from the source and transverse locations, and are discussed in terms of meandering and relative dispersion.