Drivers of ice-nucleating particle variability at urban and high-mountain environments of the Western Mediterranean

Abstract. This study presents a phenomenological analysis of immersion freezing ice-nucleating particles (INPs) at two different environments, urban (UGR) and high-mountain (SNS) stations, in Southern Spain. Measurements were conducted from June 2024 until June 2026, including INP concentration spectra and aerosol properties. The INP concentrations at UGR and SNS were consistent with previous measurements in the Mediterranean, showing a seasonal pattern. Spring shows the highest INP concentration values at high temperatures, which is likely related to the presence of biological particles. In contrast, during summer and autumn INP concentration values were higher at lower temperatures, which can be linked to the presence of Saharan dust. A correlation analysis between INP concentrations and aerosol optical properties (AOPs) revealed that at UGR there is negative correlation with the single scattering albedo (SSA), whereas for SNS there is positive correlation between INP concentrations and aerosol load proxies, such as the scattering and absorption coefficients. After calculating permutation feature importances between the INP concentrations and the AOPs, we developed parameterizations to predict INP concentrations. At UGR the parameterization is based on SSA, whereas at SNS the parameterization is based on aerosol scattering coefficient. For both parameterizations, 97 % percent of the data fall within a factor 10, and around 90 % of the data is within a factor 5, which reveals a good agreement between predicted and observed INP concentrations. These prediction schemes based on AOPs open new possibilities to extend INP estimations to observatories that routinely measure AOPs, extending the spatial and temporal coverage of INPs.