10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Effect of Dispersion & Coagulation Parameters on the Survival Fraction of Aerosol Particles Released from Puffs and Plumes
Tanmay Sarkar, S. Anand, Y.S. MAYYA, BARC
Abstract Number: 742 Working Group: Aerosol Modeling
Abstract The concept of particle survival fraction finds important application for estimating the contribution of localized emission sources to the persisting aerosol background in the atmosphere. In recent times, this concept has found an important application in the area of geo-engineering proposals in order to slow down global warming, in which light scattering aerosol plumes are supposed to be deliberately released from ships to the clouds to enhance marine cloud brightening. As the particles releases from highly inhomogeneous sources, they would undergo significant coagulation during their dispersal to form background aerosols. An effective way of quantifying this effect is to model their survival fraction by combining coagulation equation with dispersion equation. A major difficulty arises while combining aerosol microphysical processes with dispersion equation, particularly coagulation process as it leads to non-linear integro-differential equation. Several approaches have been developed by various authors in the past to solve the governing equation for particles undergoing simultaneous dispersion/Brownian diffusion and coagulation, such as analytical solutions to special cases (Simons, 1996), expanding plume models (Turco and Yu, 1999). The diffusion–coagulation equation that governs the evolution of a spatially inhomogeneous aerosol puff and plumes is solved by Anand and Mayya (2011). This model is extended to geo-engineering problems (Anand and Mayya, 2015). To make the solution methods or numerical computations simpler, several approximations on 1) particle size distribution, 2) coagulation kernel, and 3) dispersion process are made.
In the present study, we examine the effect of these parameters on the survival fraction of particles in a spherical puff through exact numerical calculations. The numerical program can consider any initial particle size distribution such as lognormal, exponential, etc., and coagulation kernels such as free-molecular and Fuchs kernels, which can handle fractals also. The diffusion coefficients for the particles released from the point sources are generally expressed as either space- or time-dependent variables. The study demonstrates that the survival fraction will be lower for an initial polydisperse spectrum as compared to a mono-disperse spectrum. The effect of polydispersity is further studied by varying the parameters of initial size distribution (CMD and GSD). The inclusion of Fuchs kernel and non-constant dispersion coefficient in the numerical program affects the evolution of particle survival fraction compared to the constant kernel case. These realistic simulations finally determine the fraction of emitted particles survived due to combined action of coagulation and atmospheric dispersion. This model is proposed to compute source emission correction factor for various indoor emission sources to estimate effective number concentration to the indoor background environment and then to global aerosol background.
References: [1] Simons, S., J. Phys. A: Math. Gen. 29, 303-307, (1996). [2] Turco, R.P. and F. Yu, J. Geophysical Res. 104, 19227-19241, (1999). [3] Anand, S. and Y. S. Mayya, Atm. Environ. 45, 4488-4496, (2011). [4] Anand, S. and Y. S. Mayya, Atmos. Chem. Phys., 15, 753-756, (2015).