Ammonium nitrate evaporation and nitric acid condensation in DMT CCN counters

Abstract

Abstract. The effect of inorganic semivolatile aerosol compounds on the cloud condensation nucleus (CCN) activity of aerosol particles was studied by using a computational model for a DMT-CCN counter, a cloud parcel model for condensation kinetics and experiments to quantify the modelled results. Concentrations of water vapour and semivolatiles as well as aerosol trajectories in the CCN column were calculated by a computational fluid dynamics model. These trajectories and vapour concentrations were then used as an input for the cloud parcel model to simulate mass transfer kinetics of water and semivolatiles between aerosol particles and the gas phase.Two different questions were studied: (1) how big a fraction of semivolatiles is evaporated from particles after entering but before particle activation in the DMT-CCN counter? (2) How much can the CCN activity be increased due to condensation of semivolatiles prior to the maximum water supersaturation in the case of high semivolatile concentration in the gas phase?Both experimental and modelling results show that the evaporation of ammonia and nitric acid from ammonium nitrate particles causes a 10 to 15 nm decrease to the critical particle size in supersaturations between 0.1 % and 0.7 %. On the other hand, the modelling results also show that condensation of nitric acid or similar vapour can increase the CCN activity of nonvolatile aerosol particles, but a very high gas phase concentration (as compared to typical ambient conditions) would be needed. Overall, it is more likely that the CCN activity of semivolatile aerosol is underestimated than overestimated in the measurements conducted in ambient conditions.

CCN closure study: Effects of aerosol chemical composition and mixing state

“…This condensed mass increases under low-temperature and high relative humidity conditions and cannot be sampled under dry conditions at ground level [Topping et al, 2013]. Even in highly polluted regions, lower concentrations of semivolatile gases and their diffusional losses inside the measurement system restrict the quantification of the increase in CCN potential due to the condensation of semivolatile products prior to cloud droplet formation in the atmosphere [Romakkaniemi et al, 2014]. A recent study by Romakkaniemi et al [2014] investigated the effects of inorganic semivolatile compounds on the CCN activity of aerosol particles by using a computational model for a droplet measurement technologies (DMT) CCN counter, a cloud parcel model for condensation kinetics.…”

“…Even in highly polluted regions, lower concentrations of semivolatile gases and their diffusional losses inside the measurement system restrict the quantification of the increase in CCN potential due to the condensation of semivolatile products prior to cloud droplet formation in the atmosphere [Romakkaniemi et al, 2014]. A recent study by Romakkaniemi et al [2014] investigated the effects of inorganic semivolatile compounds on the CCN activity of aerosol particles by using a computational model for a droplet measurement technologies (DMT) CCN counter, a cloud parcel model for condensation kinetics. They found that the evaporation of ammonia and nitric acid from ammonium nitrate particles caused a 10-15 nm decrease in critical diameter at SS = 0.1-0.7%, whereas the condensation of nitric acid vapor increased the CCN potential only in the presence of high semivolatile compound concentrations in the gas phase.…”

Droplet activation of wet particles: development of the Wet CCN approach

“…For instance, a number of studies reported evaporation (as a result of chemical decomposition) of ammonium nitrate (Mikhailov et al, 2004;Svenningsson et al, 2006;Gysel et al, 2007;Wu et al, 2013) and organic acids (Prenni et al, 2003) during H-TDMA measurements. Semivolatile compounds may also evaporate inside the CCNC (Asa-Awuku et al, 2009;Romakkaniemi et al, 2014).…”

“…Evaporation of volatile compounds after DMA sizing (inside a CCNC) would result in overestimation of D50 determined by the Dry CCN method (Asa-Awuku et al, 2009;Romakkaniemi et al, 2014). Recently, Romakkaniemi et al (2014) modeled evaporation and co-condensation inside the DMT CCNC (the same instrument as used in this study), using a computational fluid dynamics model.…”

“…Recently, Romakkaniemi et al (2014) modeled evaporation and co-condensation inside the DMT CCNC (the same instrument as used in this study), using a computational fluid dynamics model. In a test case for ammonium nitrate particles, simulation results showed that evaporation of ammonium nitrate led to a reduction in effective dry diameter by 10 to 15 nm for supersaturations between 0.1 % and 0.7 % (Romakkaniemi et al, 2014). As the first step to evaluate the impact of evaporation on the Wet CCN method, ammonium nitrate was tested experimentally (Fig.…”