Abstract
The effect of ammonia on the formation and growth of sulfuric acid nanoparticles was investigated experimentally. The nanoparticles were produced by negative corona discharge in NH3/SO2/H2O/Air mixtures. The size distribution of the uncharged particles formed by homogenous nucleation was measured using a nano-DMA. In the absence of NH3, the concentration and mean size of the formed particles increased as the concentrations of H2O and SO2 increased. With the help of mass spectrometric measurements using an ion mobility spectrometer/mass spectrometer (IMS/MS), increases in H2O and SO2 concentrations proved to lead to the formation of H2SO4. The enhancement of particle formation by the addition of NH3 was observed, but the concentration of particles was only 1.2-2.2 times higher than that without NH3. The mass spectra of negative ions showed that HSO4¯(H2SO4)n ions significantly declined in the presence of NH3, suggesting a reduction of free H2SO4 molecules. In addition, the HSO4¯ ions associated with NH3 molecules were not found in the mass spectra. These features may be explained by the rapid formation of ammonium bisulfate, which is unlikely to be negatively charged. In the growth of sulfuric acid nanoparticles, no notable effect of NH3 was observed.
