Heterogeneous uptake of the C<sub>1</sub> to C<sub>4</sub> organic acids on a swelling clay mineral

Abstract

Abstract. Mineral aerosol is of interest due to its physiochemical impacts on the Earth's atmosphere. However, adsorbed organics could influence the chemical and physical properties of atmospheric mineral particles and alter their impact on the biosphere and climate. In this work, the heterogeneous uptake of a series of small organic acids on the swelling clay, Na-montmorillonite, was studied at 212 K as a function of relative humidity (RH), organic acid pressure and clay mass. A high vacuum chamber equipped with a quadrupole mass spectrometer and a transmission Fourier transform infrared spectrometer was used to detect the gas and condensed phases, respectively. Our results show that while the initial uptake efficiency was found to be independent of organic acid pressure, it increased linearly with increasing clay mass. Thus, the small masses studied allow access to the entire surface area of the clay sample with minimal effects due to surface saturation. Additionally, results from this study show that the initial uptake efficiency for butanoic (butyric) acid on the clay increases by an order of magnitude as the RH is raised from 0% to 45% RH at 212 K while the initial uptake efficiency of formic, acetic and propanoic (propionic) acids increases only slightly at higher humidities. However, the initial uptake efficiency decreases significantly in a short amount of time due to surface saturation effects. Thus, although the initial uptake efficiencies are appropriate for initial times, the fact that the uptake efficiency will decrease over time as the surface saturates should be considered in atmospheric models. Surface saturation results in sub-monolayer coverage of organic acid on montmorillonite under dry conditions and relevant organic acid pressures that increases with increasing humidity for all organic acids studied. Additionally, the presence of large organic acids may slightly enhance the water content of the clay above 45% RH. Our results indicate that heterogeneous uptake of orCorrespondence to: C. D. Hatch (courtney-hatch@uiowa.edu) ganic acids on swelling clay minerals provides an important irreversible heterogeneous sink for these species.

Heterogeneous Uptake of Gas‐Phase Acetic Acid on the Surface of α‐Al2O3 Particles: Temperature Effects

“…At 298 K, positive bands at 1343, 1424, 1468, 1578, 2935, 2986, and 3016 cm −1 , accompanied by a broad negative band at 3706 cm −1 , indicated the formation of acetate by the consumption of surface OH groups on α‐Al 2 O 3 , based on previous studies . On lowering the reaction temperature, several changes in the spectra were observed.…”

Heterogeneous Reactions of Acetic Acid with Oxide Surfaces: Effects of Mineralogy and Relative Humidity

“…After exposure of CaCO 3 aerosol particles to CH 3 COOH(g), Prince et al 37 found that calcium acetate and CO 2 were formed on the particles and in the gas phase, respectively. The uptake of CH 3 COOH(g) onto Namontmorillonite particles was studied at 212 K, 38 and the uptake coefficients were found to increase from 1.3×10 -5 at 0% relative humidity (RH) to 6.0×10 -5 at 45% RH. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to investigate the heterogeneous interaction of CH 3 COOH(g) with α-Al 2 O 3 particles, 39 and the uptake coefficient was reported to be (6.0±0.8)×10 -7 at 0% RH.…”

HCOOH measurements from space: TES retrieval algorithm and observed global distribution

“…Photochemical loss is relatively slow (τ ∼ 25 days), so that any HCOOH formed or vented outside of the boundary layer can be transported for long distances in the free troposphere (Paulot et al, 2011). Irreversible uptake on dust can be significant under some conditions, but appears to be minor on a global scale (Hatch et al, 2007;Paulot et al, 2011). The overall atmospheric lifetime for HCOOH is estimated at 3-4 days (Stavrakou et al, 2012).…”