In Situ Electrostatic Separation of Ambiant PM2 into Source Specific Fractions During Collection in a FRM Sampler

To separate particles in any medium, some external force has to be applied. Researchers have successfully separated aerosol particles in laboratory conditions using thermophoretic forces.21,22 However, because the ambient temperature varies considerably during the FRM mandated 24 hour collection periods, the thermophoretic forces on PM2.5 will also vary with time. Triboelectrostatic separation uses triboelectrification to induce static charges onto the particles, which are then separated using electrostatic field. 23,24 Here, we propose to use electrostatic force25 to nondestructively separate PM2.5 particles during their collection. This will be accomplished by making a relatively simple modification to an existing FRM sampler (figure 1). In this method, an ionizing grid maintained at a high electric potential floods the PM2.5laden ambient air stream with electrons. Because most of the inorganic coal fly ash particles are glassy non-conductive aluminosilicate spheres or oxides of low electrical conductivity (insulators), they should rapidly accumulate electrons to acquire and retain a net negative charge. Carbonaceous and ionic species are typically more conductive and should therefore acquire significantly less charge. A dead zone between the electron flood gun (ionizing grid) and the electrostatic separation field (deflector plates) should provide enough time for further reduction of static electrical charge of the more conductive particles by moisture in the ambient air. The parallel electric field applied orthogonal to the flow direction by the electrostatic deflector plates should cause the charged particles to be deflected from flow direction. The electric field will be adjusted so that it will merely deflect the charged species and not bind them to the electrodes. After the electrostatic deflection field, the PM2.5laden stream should be separated into two parallel co-linear streams.