CAREER: Reaction Mechanisms in Model Aqueous Atmospheric Particles

Grants and Contracts Details

Description

Intellectual Merit: Due to the major role that marine aerosol plays in climate, visibility and air quality, it is essential to understand the chemical reactions occurring in these airborne particles. The proposed project will investigate important photoinduced and thermal ageing processes of aqueous á- ketocarboxylic acids (á-KA, e.g., pyruvic, glyoxylic, and oxomalonic acids) as a mechanism of formation of Humic-like matter (HULIS). A cyclic thermal and photochemical processing is used to mimic nighttime and daytime cycles of HULIS ageing that will be monitored with different instruments in the presence of important electrolytes (e.g., Na+, HN4 +, Cl-, SO4 2-) and surfactants. We will develop new fundamental understanding of chemical reaction mechanisms, as outline in a research plan based on direct, solid experimental evidence. The project will also study the production of reactive halogen species at the air-water interface. Solutions containing halides found in sea spray aerosol will be aerosolized and exposed to ozone gas to simulate the possible reactions of ozone destruction in the lower atmosphere. The project will utilize an interdisciplinary approach and tools to investigate the chemical reaction mechanisms, kinetics, and correlate chemical structure with optical properties of model systems under conditions similar to atmospheric waters. The plan includes experiments at variable temperature, pH, electrolytes, and chemical composition in the presence of TEMPO radical scavenger, and other organic compounds (aliphatic and aromatic carboxylic acids). Real time (UV-visible, FTIR, and ESI- and APCIMS measurements), as well as off-line chromatography (ion chromatography-conductivity-MS, UHPLCUV- ESI-MS, GC-MS, LC-ion trap-MS, MALDI-TOF-MS), spectrophotometric (UV-vis, FTIR, fluorescence, NMR, EPR), and CHNS elemental analyzes will report kinetic and mechanistic information. Objectives: Our expertise in physical/organic chemistry will allow us to address the following questions: 1. How does the oxidation of halides at the air-water interface proceed in aerosolized microdroplets? We will quantify the fast production of oxyacids of halogens at variable reactant and O3 concentrations. 2. What are the mechanisms of formation of HULIS produced by sunlight irradiation (ë > 305 nm) and indirect photolysis (HO•) of á-KA in aqueous solutions with electrolytes? 3. What are the optical (chromophores) and chemical properties (chemical structure) of the reaction mixtures? Do individual molecules or supramolecular interactions govern the absorption properties? 4. Do the chromophoric products behave as photosensitizers of aromatic carbonyls and acids? We will explore cross-reactions of carbonyl mixtures in the presence of oxalic acid and salicylic acid. 5. Do aldol condensation and imine formation reactions occur in our model system? Constrain any overlap with photochemical reactions of glyoxylic acid as a model compound.
StatusFinished
Effective start/end date7/1/136/30/19

Funding

  • National Science Foundation: $525,000.00

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