Urban Aerosol Particles from One of the Largest Tropical Megacities Are Able to Act as Ice Nucleating Particles Facilitating Cirrus Cloud Formation
SEBASTIÁN MENDOZA-TÉLLEZ, Bingbing Wang, Jiyu Gao, Graciela Binimelis de Raga, Luis A. Ladino, Universidad Nacional Autónoma de Mexico
Abstract Number: 386
Working Group: Aerosols, Clouds and Climate
Abstract
Mexico City (MC) is one of the largest megacities in tropical latitudes. Its size, population, large number of vehicles, diverse biota, and the variety of anthropogenic activities, result in high levels of air pollution. However, the pollutions levels, and hence, the aerosol composition has been reported to significantly differ along the city. Although northern MC is more polluted than the southern part, whether these differences in the aerosol concentration and composition could impact on cloud formation along the different local microclimates is highly uncertain. For example, the MILAGRO campaign (2006) demonstrated that polydisperse aerosol particles from northern MC were enriched in anthropogenic organic particles and that they can nucleate ice, under cirrus conditions, at relative humidities with respect to ice (RHice) and temperatures of ~122-128% and 210-230 K, respectively. However, the role of the southern aerosol particles, likely enriched in biogenic organics, in cirrus cloud formation is currently unknown.
Aiming to improve our understanding on the relationship between aerosol composition and ice nucleation in this large megacity, here we report the bulk and individual ice nucleating particles (INP) elemental composition as well as the ice nucleating abilities (via deposition nucleation) of size-selected aerosol particles collected in northern and southern MC in September of 2024. The ice nucleation experiments were carried out using the Xiamen University Ice Nucleation Chamber (XMU-INC) varying RHice between 209 and 221 K. It was found that besides the chemical composition differences between the northern and southern aerosol populations, the INP abilities of the aerosol particles from both parts of MC are rather comparable with ice formation taking place at RHice as low as 136.18% (220.52 K). Therefore, it appears that the ice nucleating abilities of these complex urban particles are not necessarily controlled by their chemical composition.