Coagulation effects of micro sized particles on the atmospheric lifetime of airborne engineered nanoparticles

Abstract

When measuring number concentrations of particles in different size modes, one will find different halftimes and / or transportation lengths. These differences are imposed by numerous mechanisms, such as dilution, deposition, nucleation, coagulation et cetera. This study points out the degree of significance of micro sized particles for coagulation of nanoparticles under various circumstances. Large particles have a higher coagulation rate per particle, but are present in lesser amounts; between these two we find a sensitive balance. An overview in extreme and regular particle concentrations is included, as well as a figure in which monodisperse coagulation effects are summarized. Particles with a diameter above 10 nm are generally not affected by any realistic amount of particulate matter with diameters above 2.5 µm. Particles with diameters above 10 µm do generally not contribute to coagulation loss of any particle, but atmospheric amounts of smaller particles do influence nanoparticles with diameters below 10 nm, such as quantum dots. Although coagulation due to micro sized particles is significant it never dominates over coagulation due to submicron particles. Monodisperse calculations appear to be of the same order of magnitude as continuous model calculations, and can function as minimum estimates.