Charged particle formation by the ionization of air containing sulfur dioxide

Experimental investigation of charged particle formation by the ionization of air containing sulfur dioxide (SO2) was performed using a nano-DMA (differential mobility analyzer) and an atmospheric pressure ionization mass spectrometer. A radioactive ion source of 241Am and a negative dc corona discharge were used to ionize SO2/H2O/air mixtures. The results showed that the number of charged particles that formed had increased as H2O concentration increased (ca. 20–3 × 103 ppm) for both ion sources, but also that the number of charged particles produced when using the negative corona discharge was more than two orders of magnitude greater than what was produced using 241Am. During ionization by α-ray irradiation, SO4−(H2O)n ions predominated coincident with the formation of charged particles. The negative corona discharge produced a more complicated ion mass spectrum, which included ion groups of NO3−, SOx− (x = 2–5) and HSOx− (x = 3–5). The relative abundance of the ion groups varied depending on H2O concentration and ion reaction time. The ions with an HSO4− core surpassed the ions of other groups as H2O concentration increased. The formations of NO3− ions and cluster ions containing HNO3 also were enhanced at higher H2O concentrations. Possible ion-molecule reactions responsible for the observed mass spectra are discussed in detail.

Experimental investigation of charged particle formation by the ionization of air containing sulfur dioxide was performed using a nano-DMA and an atmospheric pressure ionization mass spectrometer.Figure optionsDownload as PowerPoint slide