Tsai, I-C.#, J.-P. Chen*, Y.-C. Lin, C. C.-K. Chou, and W.-N. Chen, 2015: Numerical investigation of the coagulation mixing between dust and hygroscopic aerosol particles and its impacts. J. Geophys. Res. Atmos., 120, 9, 4213–4233. doi: 10.1002/2014JD022899.
A statistical-numerical aerosol parameterization was incorporated into the regional air quality model CMAQ to study the coagulation mixing process focusing on a dust storm event occurred over East Asia. Simulation results show that the coagulation mixing process tends to decrease aerosol mass, surface area, and number concentrations over the dust source areas. Over the downwind oceanic areas, aerosol concentrations generally increased due to enhanced sedimentation as particles became larger upon coagulation. The mixture process can reduce the overall single scattering albedo by up to 10% as a result of enhanced core-with-shell absorption by dust and reduction in the number of scattering particles. The enhanced dry deposition speed also altered the vertical distribution. In addition, the ability of aerosol particles to serve as cloud condensation nuclei (CCN) increased from around 107 m-3 to above 109 m-3 over downwind areas because a large amount of mineral dust particles became effective CCN with solute coating, except over the highly polluted areas where multiple collections of hygroscopic particles by dust in effect reduced CCN number. This CCN effect is much stronger for coagulation mixing than by the uptake of sulfuric acid gas on dust, although the nitric acid gas uptake was not investigated. The ability of dust particles to serve as ice nuclei may decrease or increase at low or high sub-zero temperatures, respectively, due to the switching from deposition nucleation to immersion freezing or haze freezing.
Simulated daily (March 19) mean near-surface concentrations of all aerosol particles. Panels from left to right are mass (g m-3), surface area (10-6 m2 m-3) and number (109 m-3) concentrations. Top panels are the absolute values from the coagulation-mixing run; the lower panels are the differences in results between the coagulation-mixing run and the external-mixing runs.