This work explores two aspects of the motion of particles inside a turbulent fluid flow: relative dispersion and Lagrangian correlations. These are studied experimentally, by means of custom-made miniaturized radiosondes launched in clusters to obtain data about the turbulence in the atmospheric boundary layer, and numerically, by means of Direct Numerical Simulations of a cloud's border region, modeled as a turbulent mixing layer in which the advected Lagrangian particles are water droplets. Relative dispersion is one of the open problems of fluid turbulence, concerning how fast particles are spread apart by the fluid flow. The relevant theoretical framework is Kolmogorov's and Obukhov's K41 theory, but this only holds for the case of stationary, homogeneous, isotropic turbulence.