Relation between ice nuclei particles concentration and aerosol counting at different sizes

Abstract

This work investigates the relation between the natural ice particle (IP) concentration measured between −30°C and −48°C and the aerosol number concentration in Córdoba, Argentina. Air mass back trajectories reaching Córdoba were calculated to also analyze the relation between the origin of the air masses and the behaviour of aerosol number concentration and IP concentration. For temperatures higher than −36°C, results show a clear trend of an increase in IP concentration with both decreasing temperature and increasing concentration of aerosols with aerodynamic diameter ranging from 0.5 m to 20 m (naer,0.5). For temperature ranging from −30 to −34°C a power law fit relating naer,0.5 and ice nuclei particle (INP) concentration is proposed. Based on the relationship between IP concentration and temperature for naer,0.5 at two specific concentration ranges, a change in trend was observed at temperatures below −36°C compared to higher temperatures. The small slopes at temperatures lower than −36°C indicate that heterogeneous nucleation is less important than at higher temperatures. Additionally, the fact that, at temperatures lower than −36°C, the slopes for both ranges of naer,0.5 are similar, indicate that the nucleation processes are independent of the concentration and size of aerosols. From the comparison with values previously reported, it was found that measurements obtained in the present work are at least one order of magnitude higher than estimations following the parameterization proposed by DeMott et al. (2010). The observed differences can be explained considering the uncertainties in the estimated INP concentrations, the uncertainties related to the IP measurements, and the different characteristics of the sites where measurements were performed. Considering the scarcity of INP measurements and its relationship with aerosol concentration in the Southern Hemisphere, this work provides valuable data that can be compared against field measurements or used in empirical parameterizations, constituting in both cases important contributions to improve the representation of clouds in climate models.