Articles | Volume 16, issue 2
Research article
26 Jan 2016
Research article |  | 26 Jan 2016

Influence of the ambient humidity on the concentration of natural deposition-mode ice-nucleating particles

M. L. López and E. E. Ávila

Abstract. This study reports measurements of deposition-mode ice-nucleating particle (INP) concentrations at ground level during the period July–December 2014 in Córdoba, Argentina. Ambient air was sampled into a cloud chamber where the INP concentration was measured at a temperature of −25 °C and a 15 % supersaturation over ice. Measurements were performed on days with different thermodynamic conditions, including rainy days. The effect of the relative humidity at ground level (RHamb) on the INP concentration was analyzed. The number of INPs activated varied from 1 L−1 at RHamb of 25 % to 30 L−1 at RHamb of 90 %. In general, a linear trend between the INP concentration and the RHamb was found, suggesting that this variability must be related to the effectiveness of the aerosols acting as INPs. From the backward trajectories analysis, it was found that the link between INP concentration and RHamb is independent of the origin of the air masses. The role of biological INPs and nucleation occurring in pores and cavities was discussed as a possible mechanism to explain the increase of the INP concentration during high ambient relative humidity events. This work provides valuable measurements of deposition-mode INP concentrations from the Southern Hemisphere where INP data are sparse so far.

Short summary
This work deals with the origin and nature of atmospheric ice-nucleating particles (INPs). An accurate determination of the atmospheric INP concentration is relevant since INPs induce freezing in clouds, thus initiating an efficient mechanism for cloud particles to reach a precipitating size. The effect of relative humidity on the INP concentration at ground level was analyzed and discussed.
Final-revised paper