Abstract
Abstract. Charging and coagulation influence one another and impact the particle charge and size distributions in the atmosphere. However, few investigations to date have focused on the coagulation kinetics of atmospheric particles accumulating charge. This study presents three approaches to include mutual effects of charging and coagulation on the microphysical evolution of atmospheric particles such as radioactive particles. The first approach employs ion balance, charge balance, and a bivariate population balance model (PBM) to comprehensively calculate both charge accumulation and coagulation rates of particles. The second approach involves a much simpler description of charging, and uses a monovariate PBM and subsequent effects of charge on particle coagulation. The third approach is further simplified assuming that particles instantaneously reach their steady-state charge distributions. It is found that compared to the other two approaches, the first approach can accurately predict time-dependent changes in the size and charge distributions of particles over a wide size range covering from the free molecule to continuum regimes. The other two approaches can reliably predict both charge accumulation and coagulation rates for particles larger than about 0.04 micrometers and atmospherically relevant conditions. These approaches are applied to investigate coagulation kinetics of particles accumulating charge in a radioactive neutralizer, the urban atmosphere, and an atmospheric system containing radioactive particles. Limitations of the approaches are discussed.
Highlights
Atmospheric particles play an important role in airborne transport of contaminants, such as radionuclides
We have evaluated the validity of the methods used in the three approaches to predict charge accumulation on atmospheric particles
The monovariate population balance model using the average collision efficiency can be used to simultaneously investigate charging and coagulation kinetics of atmospheric particles. These validation tests suggest that all the approaches developed can be used to reliably couple particle charging with coagulation kinetics of atmospheric particles
Summary
Atmospheric particles play an important role in airborne transport of contaminants, such as radionuclides. The effects of charging on the particle size distribution are frequently neglected in aerosol transport models involving microphysics of atmospheric particles. Alonso (1999) and Alonso et al (1998) developed analytical and numerical approaches to estimate timedependent changes in the size distributions of singly charged and neutral particles; these approaches cannot be used to investigate the coagulation kinetics of particles acquiring multiple elementary charges. None of these approaches considered self-charging; the aforementioned approaches may be subject to error when they are used to simulate atmospheric dispersion of radioactive plumes. Development, validity, application, and limitations of these approaches are discussed
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