10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Photochemical Multiphase Organonitrate Formation in Wet Particles Under Humid NOx Conditions
YONG LIM, Jihoon Seo, Jin Young Kim, Bong Kim, Barbara Turpin, KIST
Abstract Number: 454 Working Group: Aerosol Chemistry
Abstract NOx plays an important role in urban atmospheric chemistry. NOx, which is emitted from the fossil fuel combustion, affects secondary aerosol formation. Traditionally, NOx is known to be associated with gas-phase reactions forming semi-volatile products like organonitrates or ammonium nitrates, leading to secondary aerosol. Here, we discover organonitrate formation in the aqueous phase. We have conducted chamber experiments for photooxidation of wet aerosols containing glyoxal and ammonium sulfates under humid NOx conditions, and analyzed the products using high resolution quadrupole time of flight mass spectrometry (HR-Q-TOF-MS) and a scanning mobility particle sizer (SMPS). Nitric acid is dominantly formed by photooxidation of NOx and taken up into neutral wet particles substantially, resulting in dramatic hygroscopic growth at high relative humidity. In turn, increased aerosol liquid water in wet particles facilitates aqueous-phase reactions of glyoxal and dissolved nitric acid leading to organonitrate formation. We have identified several types of organonitrates formed by the reaction of glyoxal and nitric acid in the aqueous phase. We have also conducted the quantitative analysis for organonitrates by preparing standard solutions of glyoxal, nitric acid, and organonitrates from glyoxal-nitric acid mixtures with known concentrations. Using a thermodynamic model and a kinetic/equilibrium model based on smog chamber results, we have simulated ambient particle components (particularly, nitrates, organics and organonitrates) and particle acidity during the haze event at Seoul, the most urbanized city in South Korea, which is characterized by high NOx and relative humidity. HNO3 uptake into the particles and the hygroscopic growth and acidification of the particles were significant, and notably organonitrates were formed significantly. Our finding of organonitrate formation in the aqueous phase provides a new insight of secondary organic aerosol, enhancing our understanding and model predictions for organic particles, whose formation is still not well explored.