Nanometer-Sized Particle Formation from NH₃/SO₂/H₂O/Air Mixtures by Ionizing Irradiation

Abstract

ABSTRACT. Formation of nanometer-sized particles in NH,ISOJH,OIAir mixtures by a-ray irradiation was studied experimentally to evaluate the effect of NH, gas on the gas-to-particle conversion process. The total particle number concentration, the charged-particle fraction, and the electrical mobility distribution of particles generated in the ionization chamber were measured at various NH,, SO,, and H,O vapor concentrations and residence times of the gas mixture. Particle generation was enhanced in the presence of NH,, but the enhancement depends greatly on the SO,, NH,, and H,O concentrations; particle number concentrations at NH, mixing ratios of 0.71-3.6 ppm were 2-4 times higher than those in the absence of NH,, but were constant in this range of NH, concentration. The charged-particle fraction decreased with the addition of NH,, which indicated that ion-induced nucleation was decreased and homogeneous nucleation was enhanced. To evaluate the number concentrations of gaseous products, kinetic equations for the vapor species were solved on the basis of chain reactions initiated by OH radicals.

Evolution of particle composition in CLOUD nucleation experiments

“…Therefore, both O-TDMA measurements and H-TDMA measurements confirm that the particles produced in these conditions consisted of ammonium sulphate at a diameter of 150 nm. These results are in good agreement with earlier studies, as the particles formed by nucleation eventually become chemically neutral and form salt particles, such as ammonium bisulphate and ammonium sulphate if the ammonia concentration is high enough (Seinfeld and Pandis, 1998;Kim et al, 1998). Fig.…”

The role of atmospheric ions in aerosol nucleation – a review

“…Firstly the charged fractions were examined and secondly the electrical mobility distributions for positive and negative particles revealed a stronger activation by negative ions. In later work by the same group (Kim et al, 1998) the presence of NH 3 was found to enhance particle formation and decrease the charged fraction.…”

Ternary homogeneous nucleation of H<sub>2</sub>SO<sub>4</sub>, NH<sub>3</sub>, and H<sub>2</sub>O under conditions relevant to the lower troposphere

“…Even if the system has multiple chemical species, it cannot be simply assumed that nucleation would take place through THN or multicomponent processes; rather it depends on several conditions including how much these ternary species are present in the system, and sometimes nucleation can take place solely via BHN even in the presence of ternary species (McGraw and Zhang, 2008). A laboratory study has also shown that different mechanisms may occur with the same aerosol precursors, under different experimental conditions (Kim et al, 1998). A typical atmospheric example would be the upper troposphere and lower stratosphere; even when there are many other chemical species in the gas phase, ion induced nucleation dominates in this region , because of low temperatures and high ion production rates by cosmic rays.…”

“…At present, the exact [NH 3 ] needed to enhance J over BHN and the magnitude of enhancement in nucleation due to NH 3 are both uncertain, mostly because there are only a very limited number of laboratory studies of NH 3 -THN (Ball et al, 1999;Benson et al, 2009;Berndt et al, 2010;Hanson and Eisele, 2002;Kim et al, 1998). To produce particles, these experiments also used [H 2 SO 4 ] > 10 8 cm −3 , two to three orders of magnitude higher than typical atmospheric concentrations (10 5 -10 7 cm −3 ) (Erupe et al, 2010;McMurry et al, 2005 [OH] in the nucleation reactor), estimation of wall loss of aerosol precursors and nucleation time in the nucleation reactor, and particle detection with different cutting sizes.…”