Differences in the reactivity of ammonium salts with methylamine

Abstract

Abstract. The heterogeneous uptake of methylamine (MA) onto (NH 4 ) 2 SO 4 , NH 4 HSO 4 , NH 4 NO 3 and NH 4 Cl 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 NH 4 NO 3 , (NH 4 ) 2 SO 4 , and NH 4 Cl were observed at 298 K. Simple acid-base reaction for MA was found taking place on NH 4 HSO 4 . CH 3 NH 3 NO 3 and CH 3 NH 3 Cl are not stable at low pressure and have higher dissociation vapor pressure than methylammonium sulfate. The observed uptake coefficients of MA on (NH 4 ) 2 SO 4 , NH 4 HSO 4 , NH 4 NO 3 and NH 4 Cl 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 NH 4 Cl, (NH 4 ) 2 SO 4 and NH 4 NO 3 . 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 NH + 4 group.

Ozonolysis of Trimethylamine Exchanged with Typical Ammonium Salts in the Particle Phase

“…At the same time, this , which is in agreement with our previous work in which no gas-phase NH 3 was detected by a mass spectrometer, and the transformation from HSO 4 − to SO 4 2− was observed using an in situ Raman spectrometer when NH 4 HSO 4 was exposed to MA. 53 It should be noted that protonated TMA ((CH 3 ) 3 NH + ) was formed on all of these ammonium salts as both 1486 and 985 cm −1 bands were present in the corresponding IR spectra. This implies that aminium salts can be formed on all of these substrates.…”

“…16 On the other hand, although it has not been evaluated by modelers, heterogeneous uptake onto fine particles might also contribute to reduced nitrogen in particle phase due to the relative large uptake coefficients as reported previously. 22,53,66,67 Whatever the formation path is, once formed, organic nitrogen containing compounds including particulate amines nearly immediately begin the heterogeneous oxidation by oxidants in the lower atmosphere. 62 The lifetimes of alkylamines exposed to ozone in the gas phase usually vary from a few hours to several days.…”

“…Exchange or substitution reactions between amines and ammonium salts ((NH 4 ) 2 SO 4 , NH 4 HSO 4 , NH 4 NO 3 and NH 4 Cl) have been confirmed using both mass spectrometry 22 and Raman spectrometry. 23,24 The uptake coefficient (γ) of amines on coarse particles of ammonium salts is on the order of 10 −3 −10 −2 , 23,25−27 while it is close to unity with nanoscale ultrafine particles. 22 The γ of amines on organic acids (citric acid and humic acid) via acid− base reaction is 10 −5 −10 −3 depending on the type of organic acid.…”

“…It has been found that stronger acidity of particulate matter, 27 smaller steric effect with fewer substituted groups on the amines are favorable for the heterogeneous uptake of amines. 23 In addition, the uptake coefficient of amines on (NH 4 ) 2 SO 4 particles is highly dependent on the metastable (efflorescence or deliquescence) state, which is determined by the relative humidity, of (NH 4 ) 2 SO 4 . 24 Heterogeneous uptake of amines on sulfate particles may considerably alter the aerosol properties, such as leading to a transition from the crystalline to an amorphous phase and increased water uptake, considerably enhancing their direct and indirect climate forcing effects.…”

Measurement of gas-phase ammonia and amines in air by collection onto an ion exchange resin and analysis by ion chromatography

“…Short-chain alkyl amines have been shown to displace ammonia in particles (Bzdek et al, , 2011Chan and Chan, 2012;Liu et al, 2012;Lloyd et al, 2009), which enhances their importance in particle formation and growth. Although amines are short-lived in the atmosphere due to oxidation by common atmospheric oxidants such as OH and O 3 (Nielsen et al, 2012;Tang et al, 2013), amines and the precursors to sulfuric and methanesulfonic acids (Bates et al, 1992;Ge et al, 2011a;Ni et al, 2012) are in sufficiently close temporal proximity in the atmosphere that they are important contributors to particle formation.…”