The role of surface molecular hydrates in the heterogeneous interaction of NH3 with sulfuric acid monohydrate

Abstract

The interaction of gaseous NH 3 with thin films of sulfuric acid monohydrate (SAM, H 3 O + HSO 4 À ) in the 200-230 K range has been monitored by infrared spectroscopy and secondary ion mass spectrometry. The reaction occurs with the formation of the characteristic IR spectral features of the NH 4 + and '' salt '' bisulfate ions, whilst loss of H 3 O + and an additional surface species is observed. The evolution of the spectral features with time suggest that two processes are occurring at the uppermost surface layers, with a rapid initial reaction which saturates as the amount of available reactants on the surface is reduced and a slower continuous process which depends upon the transport of new reactants to and the removal of reaction products away from the surface. By comparison with the IR spectra of a variety of sulfuric acid hydrates, a surface reaction scheme is proposed and the implications of these observations for the reaction of condensed acids (sulfate aerosol) with bases in the atmosphere is discussed.

Photochemical Oxidation of Water-Soluble Organic Carbon (WSOC) on Mineral Dust and Enhanced Organic Ammonium Formation

“…where d[NH 4 + ]/dt is the formation rate of NH 4 + and can be translated by the IC results, A S is the particle reactive surface area, [NH 3 ] is the reactant concentration, v NH 3 is the mean velocity of NH 3 molecule, R is the gas constant, T is the temperature, and M NH 3 is the relative molecular mass of NH 3 . More details are available in Table S5.…”

“…The expanding agricultural (livestock production, fertilizer application) and nonagricultural (urban waste, fossil fuel-related exhaust) activities aggravate the pollution of ammonia (NH 3 ) and further broaden the existence of ammonium (NH 4 + ), which dominates particle mass and influences aerosol neutralization. − Some studies attempted to simulate the heterogeneous/multiphase reaction of sole NH 3 on model aerosols. − Meanwhile, pioneers explored the atmospheric uptake of NH 3 in the coexistence of inorganic acidic gases (SO 2 , NO 2 ), involving the earlier research on aqueous media , and the recent work on particle phase. − Unfortunately, the effects of organics on the uptake of NH 3 remain uncertain (Table S1). Sauerwein et al investigated the competitive adsorption of NH 3 and dimethylamine on sulfuric and oxalic acid particles, which was severely influenced by the neutralization extent and the particle phase state .…”

Atomic spectrometry update. Atomic mass spectrometry

“…No matrix effect on the measured isotopic ratio and its precision was observed in the analysis of solutions (0.5-100 ng ml 21 in 4% HNO 3 ) of isotopic Pb and Rb, with or without added matrix (110 mg l 21 Na). Under steady state conditions (30 s integration, n w5), the best possible precision (RSD) for isotopic ratios was 0.08, 0.49, 0.04 and 0.07% for 85 Rb: 87 Rb, 204 Pb: 206 Pb, 207 Pb: 206 Pb and 208 Pb: 206 Pb, respectively, using the analogue detection mode. In transient mode, the corresponding precisions were 0.2, 0.1, 0.3 and 0.3% RSD, respectively.…”

“…The in situ study of the reaction between thin layers of sulfuric acid monohydrate with gaseous ammonia allowed the kinetics of this environmentally important process to be determined. 204 Self-assembled monolayers (SAM) of sulfuric acid on gold were mounted on a cold stage at 200 K and exposed to 10 29 mbar of ammonia in the TOF S-SIMS sample chamber. Bombardment with 7.5 keV Ar 1 primary ions generated molecule-specific adducts of sulfuric acid, water and ammonia up to m/z 250.…”

Simultaneous spectroscopic detection of adsorbed and gas-phase species during atmospherically relevant heterogeneous reactions

“…The substrate probe is based upon the attenuated total internal reflection infrared (ATR-IR) spectroscopy. 25 In an atmospheric chemistry context, this method has previously applied by Horn et al with considerable success to the study of phase transitions in and reactions upon low temperature sulfuric acid hydrates, [26][27][28][29] whilst in more general physical chemistry, it has been used to examine uptake and reaction upon colloidal particles by McQuillan et al [30][31][32] ATR-IR relies upon the the interaction between the evanescent wave generated by a IR beam propagating in a transparent waveguide and material in the vicinity of the waveguide surface. As a result of an extremely short effective path length for the evanescent wave in the ambient medium, the technique is largely insensitive to gasphase material close to the waveguide surface.…”