Atmospheric Chemistry Program Seminar: Romulo Cruz-Simbron, Volkamer Group

Particle formation from reactive uptake of small molecules: HIO2 and glyoxal 

Romulo Cruz-Simbron

Atmospheric new particle formation (NPF) is a widespread phenomenon with climatic implications. These particles promote cloud formation (cloud condensation nuclei number, CCN) and increase cloud lifetimes. Uncertainty about aerosols' climate impact arises from limited knowledge of aerosol formation kinetics and the scarcity of vapors capable of nucleating particles. Studying vapors that participate in early particle formation and growth can give key mechanistic insights. The nucleation process involves vapor supersaturation and condensation to form unstable molecular clusters that, once they reach a critical size, will grow or be lost by coagulation. Studies at the CLOUD Chamber at CERN have revealed the critical role of iodous acid (HIO2) in stabilizing particle formation from iodic acid (HIO3) and sulfuric acid (H2SO4). However, atmospheric models are currently not able to predict iodine particle formation, and incompletely predict iodine-sulfur synergies. Despite recent progress on HIO3, the gas-phase formation mechanism for HIO2 currently remains unknown. We use a combination of simulation chamber experiments at CLOUD, chemical box modeling, and theoretical calculations to propose a new reaction coordinate for HIO2 formation in the gas phase under atmospherically relevant iodine radical concentrations. Transition state theory is used to predict reaction rates that are compared with the empirically derived reaction rates needed to replicate experimental results from the CLOUD13 and CLOUD12 campaigns.

During the CLOUD 16 and CLOUD 17 campaigns, the role of glyoxal reactive uptake in new particle formation and early growth was explored in the presence of sulfuric acid and ammonia under ATAL conditions (Asian Tropopause Aerosol Layer). Preliminary results are presented about the gas-phase oxidation of glyoxal, highly oxidized molecules, nucleation and early growth rates that shed new insights into multiphase chemical reactions in the sulfuric acid-ammonia system.