Trajectory models and the deformation of air parcels

A long-standing problem in the use of Lagrangian air quality trajectory models is assessing the validity of the concept of an air parcel that maintains its integrity over a certain travel time. This issue is addressed by simulating the advection and diffusion of an inert air parcel in a flow generated by a planetary boundary layer model. Measures of the difference between the actual concentration distribution of the parcel and those resulting from two forms of trajectory models are introduced.