Reactive Uptake of Dicarbonyls by Atmospheric Aerosols

Description

Secondary organic aerosols (SOA) are dominant components of atmospheric particulate matter (PM2.5). Glyoxal and methylglyoxal are the most abundant dicarbonyls in the atmosphere and their ability to form SOA via heterogeneous processes has been demonstrated. However, typical studies of glyoxal/methylglyoxal uptake into particles to form SOA were based on separate single vapor uptake laboratory experiments under controlled conditions. The co-uptake of binary vapor mixtures can be very different from that of single vapor. For example, it has been reported that the reactive uptake of glyoxal and pinanediol significantly increasedduring the co-uptake process compared to the unary vapor uptake. The reactive couptake of glyoxal and methylglyoxal into seed particles has not been studied, even though they naturally co-exist in the atmosphere. Further investigations, particularly onthe effects of different atmospheric conditions (e.g., pH, relative humidity (RH), seed particle type, and dark/irradiation), on co-uptake and subsequent SOA formation are needed. In this proposed project, we will investigate the reactive uptake of glyoxal and methylglyoxal, SOA and brown carbon (BrC) formation, and changes in physical properties of seed particles during and after the co-uptake process. Typical secondary fine mode particles of (NH4)2SO4 and NH4NO3 and coarse mode fresh and aged seasalt particles of NaCl, NaNO3, and Na2SO4 will be used as seed particles. The uptake experiments (i.e., co-uptake and single-gas uptake) into seed particles will be performed under different atmospheric conditions. An electrodynamic balance will be used to determine the reactive uptake rates/coefficients of glyoxal and methylglyoxal. Hygroscopic measurements as a function of both increasing and decreasing RH and the deliquescence and efflorescence RH will also be made. In addition, an in-situ Raman/Flow cell system will also be used to characterize the evolution of particle composition, reactant/products concentration, and particle morphology (phase state) during the co-uptake. Moreover, bulk-phase reactions will be performed to determine the kinetic parameters (e.g., rate constant) of reactions, which will be used for uptakeexperiments to estimate uptake coefficients of glyoxal and methylglyoxal and their contribution to SOA. The proposed study will provide information on the potential synergy of the reactive uptake of glyoxal and methylglyoxal and their contributions to the SOA and BrC formation. Parameters (e.g., uptake coefficient, hygroscopicity, and optical properties) will be determined. They are useful for improving the air quality model predictions of glyoxal/methylglyoxal-derived SOA in the future.