AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Oxidation of Reduced Sulfurs and Amines: Characterization and Mechanism Development
PAUL VAN ROOY, Kathleen Purvis-Roberts, Philip Silva, Matthew Nee, David R. Cocker III, University of California, Riverside
Abstract Number: 709 Working Group: Aerosol Chemistry
Abstract Gas-phase amines (trimethylamine, diethylamine, butylamine, ammonia) and reduced sulfur compounds (dimethysulfide, dimethyldisulfide) are both present over agricultural land and are both thought to be important to new particle formation and particle growth. Despite this, there is a lack of knowledge on how these compounds oxidize in the atmosphere individually nor is there a mechanism by which these compounds interact to form aerosol. To begin to fill this information gap, a 37.5 cubic meter Teflon chamber was utilized to run hydroxyl radical and nitrate radical oxidation experiments of each compound individually as well as interaction experiments containing at least one amine (100ppb) and one reduced sulfur (100ppb). Methanesulfonic acid is considered an important product of reduced sulfur oxidation however, under extreme dry conditions and in the presence or absence of NOx, methanesulfonic acid did not form. Measurements made using the HR-TOF-AMS present sulfur-containing organic fragments, such as C2H6S and C2H6SO, that cannot be explained by the current mechanism. Only when humidity as well as NOx was introduced into the chamber did methanesulfonic acid form. Interestingly, precursor decay was much faster in the presence of NOx, indicating that O(3P) plays an important role in oxidation of reduced sulfurs during chamber experiments, which are often run at high NOx concentrations. Addition of an amine to the system allows for methanesulfonic acid formation under dry, NOx-free conditions. Interactions between amines and reduced sulfur compounds results in aerosol mass concentrations up to 10 times higher than individual precursor oxidation. The addition of humidity to interaction experiments resulted in up to 4 times the mass formed during dry experiments. An updated mechanism for reduced sulfur oxidation is proposed along with a particle-forming mechanism for amines in the presence of reduced sulfurs.