AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
A Laboratory and Modeling Investigation on the Effects of Amine Uptake on SOA Composition and Its Potential Impacts on Air Quality
JULIA MONTOYA-AGUILERA, Natalie Smith, Shupeng Zhu, Donald Dabdub, Sergey Nizkorodov, University of California, Irvine
Abstract Number: 220 Working Group: Aerosol Chemistry
Abstract Inorganic nitrogen contributes significantly to particulate matter (PM) and is represented in air quality models. Less understood is the contribution of nitrogen-containing organic compounds (NOC) to secondary organic aerosols (SOA), a major component of PM. Reactive uptake of reduced nitrogen compounds by SOA, specifically ammonia (NH3) and amines, leading to the formation of NOC remains unaccounted for in air quality models. Atmospheric NH3 is ubiquitous and expected to rise due to intensifying use of NH3-based fertilizers. This uptake is important to characterize because of its potential effects on SOA composition and ability to reduce NH3 contribution to inorganic PM formation.
Uptake of NH3 and dimethyl amine (DMA) by SOA was investigated in this study. Anthropogenic (toluene, n-hexadecane) and biogenic (limonene, cedrene) volatile organic compounds were oxidized in a smog chamber at various relative humidities (0-50%). After initial SOA formation, a pulse of NH3 or DMA was introduced into the chamber. Mass spectrometry was used to characterize chemical composition in the gas phase (proton-transfer-reaction time-of-flight mass spectrometer) and particle phase (time-of-flight aerosol mass spectrometer). An NH3 analyzer measured NH3 or DMA decay. The kinetics of the NH3+SOA→NOC reactions depended on the SOA system, with measured uptake coefficients of 10-5 to 10-3. Overall, DMA uptake was greater than NH3 uptake by toluene, limonene, and cedrene SOA. The Community Multiscale Air Quality Modeling System with a continental U.S. domain indicated that inclusion of NH3+SOA→NOC chemistry decreases the concentration of inorganic components of PM2.5 but increases biogenic SOA, especially in the southeastern U.S.
While some of the NH3 uptake by SOA results were published in 2018, the DMA results are new and will be presented at AAAR for the first time.