Negative atmospheric ions and their potential role in ion‐induced nucleation

Abstract

[1] Mass identified ion cluster distributions were measured under ambient atmospheric conditions and compared with model predictions based on laboratory ion cluster thermodynamics data. The results are shown from several days where atmospheric sulfur concentrations were high and thus ion-induced cluster growth was anticipated. Atmospheric gas phase sulfuric acid, temperature, relative humidity, SO 2 , mobility distributions of ions and small charged particles, and aerosol size distributions were also measured in support of the model calculations. The relative agreement of measurement and model for the first and second sulfuric acid clusters (HSO 4 À (H 2 SO 4 ) m ) for m = 1 and 2 is quite good but suggests that sulfuric acid clustering may not occur at the collision rate. Clusters for higher m values were not observed, which is also consistent with model predictions for the conditions under which measurements were performed. The lack of both observed and predicted large ion clusters is also consistent with the independent measurements of ion mobility distributions and particle size distributions, which showed similar numbers of positively and negatively charged ultrafine particles, suggesting that neither positive nor negative ion-induced nucleation processes were likely to have contributed significantly to observed new particle formation rates during this study. The relatively low observed concentrations of the bisulfate ion also suggest that the processes leading to the first sulfuric acid/bisulfate cluster (HSO 4 À H 2 SO 4 ) may be more complicated than simple sulfuric acid clustering or exchange reactions. While nucleation was observed on some days, measurements suggest that ion-induced nucleation did not contribute significantly to new particle production or growth during these events. This does not rule out the possibility that ion-induced nucleation could contribute significantly to atmospheric new particle formation under very different atmosphere conditions such as in areas with much lower temperatures and higher ion concentrations.

Charged and total particle formation and growth rates during EUCAARI 2007 campaign in Hyytiälä

“…However, our result is in disagreement with model studies of ion-mediated nucleation by . The dominance of the neutral over the ion-induced nucleation is in agreement with the observations by Eisele et al (2006) at an urban site in Atlanta Georgia.…”

The role of ammonia in sulfuric acid ion induced nucleation

“…On the other hand, when we move toward ground level conditions ( G 3 ), this barrier grows, and probably plays a role in determining nucleation rates. In field measurements carried out by Eisele et al (2006) at ground level, a large amount of (H 2 SO 4 ) 2 ·HSO − 4 was detected, but no larger ionic cluster could be found: the authors thus concluded that ion induced nucleation does not play an important role in particle formation at those conditions. These observations are in agreement with our results that at representative ground-level conditions, ion induced nucleation is not a barrierless process, so the clusters grow to a local minimum and then prefer to stay there rather than grow further.…”

New particle formation and ultrafine charged aerosol climatology at a high altitude site in the Alps (Jungfraujoch, 3580 m a.s.l., Switzerland)

“…The attractive potential between ions and ions and between ions and the dipole moment (induced or not) of the condensable vapor reduces the thermodynamic barrier for nucleation and hence, enhances the condensational growth (Lovejoy et al, 2004;Nadykto and Yu, 2004). Conflicting views about the relative importance of IMN subsist between modelling studies (see for example Laakso et al, 2002;Harrisson and Carslaw, 2003;Yu et al, 2008) which assess that IMN should be an important source of atmospheric particles and field measurements (see for example Eisele et al, 2006;Manninen et al, 2009) who show that the contribution of IMN to new particle formation in planetary boundary layer (PBL) is less than 10% in average. In any case, the charged fraction of clusters and particles is a good indicator of the presence of neutral clusters and particles.…”

“…The monitored parameters include thirty minute averaged concentrations of NO, NO 2 , NO x and O 3 , and daily averaged concentrations of SO 2 , aerosol sulfur, and particulate matter with aerodynamic diameter below 10 µm (PM10). Neutron measurements were performed on the terrace of the Sphinx laboratory with an IGY neutron monitor which is composed by 18 counter tubes (Flückiger and Bütikofer, 2009).…”