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Role of Organic Acid-Amine Reactions in Atmospheric New Particle Formation
SANDRA FOMETE, Coty Jen, Carnegie Mellon University
Abstract Number: 133
Working Group: Aerosols, Clouds and Climate
Abstract
Atmospheric New Particle Formation (NPF) plays a critical role in climate, air quality and human health. Though aerosols play an important role in climate change, the mechanisms behind aerosol particle formation in the atmosphere are still not well understood. Studies have identified sulfuric acid, water, oxidized organics, and ammonia/amines as main precursors to nucleation of freshly formed aerosol particles in the atmosphere. However, the role of organic diacids such as oxalic and malonic acids on atmospheric NPF has not been extensively explored. Oxalic (OxA) and malonic acids (MaA), which are naturally and anthropogenically produced, are much higher in concentration than sulfuric acid (~10^10 vs ~10^6-10^8 cm-3 respectively) in the atmosphere. In addition, computational chemistry studies predicts that organic diacids can react with amines in the atmosphere to form stable organic salts in the absence of sulfuric acid. In this study, we examined nucleation reactions of malonic and oxalic acids with mono and diamines at various relative humidity values. These nucleation reactions were carried out in a clean laminar flow reactor operated at ~298-300K. The chemical composition of the freshly nucleated clusters in the flow reactor were analyzed using a custom-built, transverse chemical ionization atmospheric pressure interface long time of flight chemical ionization mass spectrometer (Cluster CIMS). A nanoparticle sizer and counter, which can measure down to ~1 nm in diameter, was used to analyze the effect of OxA and MaA on the rate of formation and growth of particles in the flow reactor. Contrary to computational predictions, no new particles form from diacid-amine nucleation reactions. However, addition of sulfuric acid to the dicarboxylic acid-amine reaction system leads to a higher particle formation rate and growth rate compared to the previously studied sulfuric acid-diamine binary nucleation system. Results from this study improves current understanding of how new particles form in the atmosphere and will enable improvements in current regional and global models that predict climate change.