Critical Role of Dust Induced Electrostatic Coagulation in the Evolution of Aerosol Size Distributions in the Atmosphere

Abstract. Coagulation modifies the particle size distributions (PSD) of atmospheric aerosols, affecting their optical properties, cloud droplet activation, and gravitational deposition. While Coulomb forces may impact coagulation processes between charged aerosols, such as dust, most coagulation models neglect the effects of aerosol charge. Here, we address the lack of single-particle charge measurements for dust aerosols by developing a method to retrieve their joint size-charge distributions. By incorporating aerosol charge into the coagulation kernel, simulations in a dust-only scenario at typical environmental concentrations show that, on hourly timescales, electrostatic force leads to a reduction of up to ~64 % in number concentration relative to Brownian coagulation. Moreover, electrostatic coagulation between dust and ambient sub-500 nm aerosols modifies the latter's PSD by ~10 % compared with Brownian coagulation. These results strongly suggest that electrostatic coagulation should be considered in air quality models.