Characterization of Ice Nucleating Particles in Rainwater, Cloud Water and Atmospheric Aerosols in Mexico City and a High-Altitude Observatory

EMMA NEGRETE HARPER, Graciela Binimelis de Raga, Rocio Garcia, Luis A. Ladino, Universidad Nacional Autonoma de Mexico

     Abstract Number: 144
     Working Group: Aerosols, Clouds and Climate

Abstract
The presence of ice in clouds is essential for the development of precipitation. This is why it is vitally important to characterize aerosol particles that act as ice nucleating particles (INPs) as well as their spatial and temporal variability. Even though some recent studies have reported the INP variability in Mexico City (MC) and Altzomoni (ALTZ, a high-altitude atmospheric observatory at 4,000 m a.s.l. in Mexico state), INPs have not been comprehensively analyzed during the rainy season (i.e., from June to October). Considering that most extreme precipitation events (including hail storms) happen during this time, it is necessary to improve the INP characterization during the rainy season. It is also necessary to increase the number of INP observations in tropical latitudes as most of the currently available INP studies were conducted at higher latitudes.

Aerosol, rainwater, and cloud water samples were collectedin MC and ALTZ for the 2022 and 2023 rainy seasons to characterize the INP populations. Additionally, the characteristics of INPs inside the planetary boundary layer were determined and compared against those in the free troposphere in ALTZ. Cloud water had the highest INP concentrations of all types of samples included in this study. Biological INPs influencing the freezing temperatures was evident in rain and cloud water samples collected in ALTZ, with some samples having onset freezing temperatures as high as -5.6°C. Samples from ALTZ have higher concentrations of INPs for the evaluated temperature range compared with literature data collected during the dry season in MC.