Development of an aerosol density separator

摘要

In many applications information about aerosols like the mass concentration or an equivalent diameter distribution is insufficient.In particular,particle shape may strongly influence the behaviour of the aerosol.Particles that are fractal-like aggregates have an open structure with a high surface-to-volume ratio,which provides a large area for surface chemistry,potentially resulting in enhanced toxicicity.Aggregated particles present in urban air are always man-made,and it is useful to determine their fraction of the total aerosol concentration .Aggregates with a fractal dimension of 2 or smaller have a similar aerodynamic behaviour as the primary particles of which they consist,while their drag coefficient or inverse mechanical mobility is approximately the sum of the drag coefficients of the primary particles.The combination of the small aerodynamic diameter and the large mobility equivalent diameter allows these particles to penetrate to the lower parts of the lung.Particles originating from combustion form aggregates with 10~2-10~5.spherical primary particles (Schmidt-Ott,1988).They originate mainly from industry and automobiles.Spherical compact particles are either of natural origin or from in photochemical atmospheric reactions involving pollutant gases.This investigation focuses on development of a device,which distinguishes between aggregated and spherical particles in the atmosphere.