Efficient Multiple Charging of Diesel Particles by Photoemission

Particle charging of real combustion aerosols by exposure to ultraviolet irradiation has been investigated. Using a tandem mobility analyzer (TDMA) we determined charge distributions as function of particle size (d = 60, 75, 90, and 120 nm) and relative intensity of the irradiation for two photon energies (hl!= 5.6 and 6 eV). For diesel particles a significantly higher charge level was achieved by photoemission compared to the calculated charging mechanism of ion attachment due to corona discharge. For example, we obtained an average charge per particle of up to 25 elementary units on particles with 100 nm in diameter