We present the first experimental observation of exact backscattering of light by an ensemble of particles in ambient air. Our experimental set-up operates in the far-field single scattering approximation, covers the exact backscattering direction with accuracy (θ = π ± ε with ε = 3.5 × 10(-3) rad) and efficiently collects the particles backscattering radiation, while minimizing any stray light. Moreover, by using scattering matrix formalism, the observation of the particles UV-backscattering signal allowed to measure the particles depolarization of water droplets and salt particles in air, for the first time, in the exact backscattering direction. We believe this result may be useful for comparison with the existing numerical models and for remote sensing field applications in radiative transfer and climatology.