Differences in the reactivity of ammonium salts with methylamine

Y Liu,J Ma,H He,C Han,C Liu,Q Ma

doi:10.5194/acp-12-4855-2012

Abstract

Abstract. The heterogeneous uptake of methylamine (MA) onto (NH4)2SO4, NH4HSO4, NH4NO3 and NH4Cl was investigated using a Knudsen cell reactor coupled to a quadrupole mass spectrometer, in situ Raman spectrometer and theoretical calculations. Exchange reactions were observed between MA and NH4NO3, (NH4)2SO4, and NH4Cl were observed at 298 K. Simple acid-base reaction for MA was found taking place on NH4HSO4. CH3NH3NO3 and CH3NH3Cl are not stable at low pressure and have higher dissociation vapor pressure than methylammonium sulfate. The observed uptake coefficients of MA on (NH4)2SO4, NH4HSO4, NH4NO3 and NH4Cl at 298 K were measured to be 6.30±1.03×10−3, 1.78±0.36×10−2, 8.79±1.99×10−3 and 2.29±0.28×10−3, respectively. A linear free energy relationship was found for the heterogeneous reactions between MA and NH4Cl, (NH4)2SO4 and NH4NO3. Namely, the natural logarithm of uptake coefficients of MA on these ammonium salts is linearly related to the electrostatic potential of the H atom in the NH4+ group.

Highlights

Recent field measurements suggest that organic nitrogen species may be an appreciable fraction of organic aerosol mass (Beddows et al, 2004; Chen et al, 2010; Pratt et al, 2009; Smith et al, 2010; Wang et al, 2010b)
We investigated the heterogeneous uptake of MA on NH4HSO4, (NH4)2SO4, NH4NO3 and NH4Cl to understand the effect of ammonium salts on their reactivity with MA
The heterogeneous reactions of MA on the typical ammonium salts including (NH4)2SO4, NH4HSO4, NH4NO3 and NH4Cl were investigated by using Knudsen cell reactor, Raman spectroscopy and theoretical calculations

Summary

Introduction

Recent field measurements suggest that organic nitrogen species may be an appreciable fraction of organic aerosol mass (Beddows et al, 2004; Chen et al, 2010; Pratt et al, 2009; Smith et al, 2010; Wang et al, 2010b). Amines are an important class of organic nitrogen species, and are frequently detected in aerosols, rainwater, and fog water (Ge et al, 2011a). They are emitted into the atmosphere from a variety of sources including livestock, biomass burning, sewage treatment, meat cooking, automobiles, industrial processes, and marine organisms (Ge et al, 2011b). Some amines, such as TMA and triethylamine (TEA), significantly contribute to secondary organic aerosol formation by NO3 (Silva et al, 2008), OH or O3 oxidation (Murphy et al, 2007; Gai et al, 2010). Wang et al (2010c) proposed that a Mannich reaction between amines and carbonyl compounds probably leads to the formation of nitrogen containing species with high molecular weight in secondary organic aerosols

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