Abstract
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.
Highlights
Natural ice-nucleating particles (INP) are considered important in atmospheric processes since they induce freezing in clouds, initiating an efficient mechanism for cloud particles to reach a precipitating size
From the studied period, variations in RHamb are not explained because of the origin of the air masses. This is to say that the relation between INP concentration and the ambient relative humidity is independent of the origin of the air masses
This fact discards the possibility that the increase in INP concentration is due to changes in the sources of the aerosols acting as ice-nucleating particles
Summary
Natural ice-nucleating particles (INP) are considered important in atmospheric processes since they induce freezing in clouds, initiating an efficient mechanism for cloud particles to reach a precipitating size. In the contact-freezing mode, ice is formed by the collision of cloud droplets with interstitial aerosols within the cloud. When the environment is supersaturated with respect to ice and subsaturated with respect to liquid water, ice deposits on the INPs directly from the vapor phase. This last mode is known as deposition nucleation. Measurements performed in the regime below water saturation are important in the understanding of deposition nucleation (DeMott et al, 2011)
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