1. Thunderstorm Dynamics Group Atmospheric ions and new particle formation For RAC meeting, Presented by Deveandraa Siingh The New particle formation (NPF) frequency was higher at Pune (26%) than that at Kanpur (14%), both comparable to the observed frequency in summer (June- August) months globally. Particle number concentrations at Pune were higher than those observed at Kanpur, whereas the condensation sink was higher at Kanpur compared to that at Pune. This is because of the higher anthropogenic sources of large aerosol particles (e.g. biomass/ biofuel burning and cooking, besides the traffic emissions). The particle formation rates were generally found higher at Pune, whereas the growth rates were higher at Kanpur. The presence of pre-existing large particles at Kanpur than at Pune suppressed formation rates and favored particle growth. The derived GR and J 5 ranged from 3.4 to 13.3 nm h -1 and 0.4 to 13.9 cm -3 s -1, respectively, which were also comparable to typical values reported in urban areas. An examination of two nucleation criteria for NPF event occurrence indicated that lower CS, lower RH, and higher H 2 SO 4 vapor source were the most favorable conditions for NPF to occur at these sites.. Particle nucleation can occur in urban environments when condensation sink is sufficiently reduced, consistent with previous study in India. Overall, NPF occurred at lower condensation sink, lower RH, higher solar radiation, and higher temperature Observations of new particle formation at two distinct Indian sub continental urban location Atmospheric ions and new particle formation events at a tropical location, Pune, India Q. J. Royal Met. Sco., 141, 3140-3156, 2015 Time variation of ion size distributions and concentrations of both positive and negative polarities for a typical type of truncated banana event observed here on 2 May 2012. The traditional banana-type events are typically observed when NPF occurs over a large spatial scale and indicate regional particle formation and growth. The growth of freshly formed particles during the early stage of NPF is due to condensation of vapour on the existing particle surface while the total number concentration declines in the later stages of NPF mainly because of their coagulation with large particles In the NPF events, growth rates of 3.9–25.3 nm positive(negative) ions are on the average ∼ 49–142 % (49–126 %) greater than those of 25.3–47.8 nm positive (negative) ions.. The ion concentrations of each polarity exhibited a maximum in the early morning between 0500 and 0800 LT on 2 May, total ion concentration kept increasing for the next 3–4 h and maintained those high values for the whole day. Diurnal variations of aerosol particle size spectra During the same NPF events, average rates of growth of positive (negative) ions ranged between 5.8 and 10.7 (6.1 and 11.1) nm/h for ions in the size range of 3.9–25.3 nm and between 3.1 and 7.6 (3.1 and 8.9) nm/ h for ions in the size range of 25.3–47.8 nm. So, growth rates of positive (negative) ions were 5.1–25.3% (1.1–60.6%) higher than for particles in the size range of 3.9–25.3nm and 9.5–22.5% (9.6–55.8%) higher than for particles in the size range of 25.3–47.8 nm. Total ion concentrations were approximately double on event days than on non-event days. Ions in the intermediate size range attach with aerosol particles. As a net result of the ion–ion recombination, ion–aerosol particle attachment, and other processes such as advection, concentrations of ions and particles in this size range become almost equal to each other during 0400–0800 LT. Thus Boltzmann charge distribution breaks down for particles in this size range. The common size range in the ion and aerosol measurements the hourly averaged size distributions of both ions of either polarity and aerosol particles measured by NAIS and SMPS, respectively, on 2 May 2012. The size range of ∼ 3.85–47.8 nm was covered in simultaneous measurements of both instruments. The size-distribution functions, dn/dlogD, of small and big cluster ions (<1.7 nm) soon after the generation of ions under stratified conditions at night-time, keep decreasing with the ion diameter, from 2000 to 0900 LT, presumably by recombination of oppositely charged ions and/or their conversion to large ions by attachment to aerosol particles. After attaining a peak at 7.4 nm, the dn/dlogD values for ions experience a rapid but short fall but then again keep their increasing trend, though at a rate slower than that of ions of diameter from 1.6 to 7.4 nm. The short fall at 7.4 nm diameter shows that although the formation of intermediate ions ceases at this size which is the upper size-limit of this ion category, their dissipation by recombination/combination processes continues. This trend in ion distribution was observed on all days of the NPF events during our observation period. Charged nanoparticles produced by splashing of raindrops, JGR-Atmos. 120, 6669-6681, 120 The mobility distribution of ions generated by splashing of raindrops is investigated.. Ion concentration of all categories increases as the rain intensity increases to ~ 50–60 mm/h and then tends to level off for higher rain intensities. Negative ion concentration is always more than that of positive ions. However, positive small ions of mobility ≥ 2– 3 cm2/Vs which are also generated during splashing are more numerous than negative ions. Our observations show that the mechanism responsible for the generation of intermediate ions is more efficient than that for the generation of heavy large ions during periods of high rain intensity. Relative roles of Lenard and Blanchard effects are suggested in generating excess of negative intermediate ions in the initial stages and excess of positive cluster ions, in the later stages of a rain shower, respectively. both positive and negative ions and charged aerosol particles are generated in all mobility ranges when raindrops splash on the Earth’s surface Average variations of fraction concentration of different categories and all categories of ions with rain intensity The concentrations of intermediate ions of both polarities increase with rain intensity, concentration of positive heavy large ions is higher than those of negative ions during low rain intensity periods but lower during high rain intensity periods. The observation suggests that either the mechanisms responsible for the generation of intermediate and heavy large ions are different or more of the positive heavy large ions are neutralized by the excess of negative intermediate ions. The former reason seems to be more likely since had the decrease in positive heavy large ion concentration during heavy rain might have been because of their neutralization by negative intermediate ions, similar reduction might have occurred in positive cluster ion concentration due to their neutralization. the space charge generated during splashing is small unless rain becomes heavy, and the space charge values agreed well with those of ion counting in heavy rain,the space charge appears only in heavy rain.