Mechanism and Kinetics of Heterogeneous Reactions of Unsaturated Organic Acids on α‐Al₂O₃ and CaCO₃

Abstract

Heterogeneous reactions have a vital role in the atmosphere due to their significant effects on the evolution of atmospheric aerosols, which in turn contribute to air pollution. However, the mechanism and kinetics of these processes involving unsaturated organic acids, important types of volatile organic compounds, are still unclear. In this work, the heterogeneous uptake of two representative atmospheric unsaturated organic acids (acrylic acid and methacrylic acid) on mineral aerosols including α-Al O and CaCO are investigated using a Knudsen cell reactor and an in situ diffuse reflectance infrared Fourier transform spectrometry (DRIFTS) reactor. The corresponding reaction pathways are proposed from the DRIFTS analysis. In addition, the initial uptake coefficients of unsaturated organic acids and their heterogeneous fate are obtained for the first time. Our results suggest that heterogeneous reactions on α-Al O and CaCO can be important sinks for acrylic acid and methacrylic acid, as well as possible contributors to the organic coating found on atmospheric aerosols, especially in high-pollution events.

Interaction of Acrylic Acid and SO2 on the Surface of Mineral Dust Aerosol

“…The heterogeneous reaction of acrylic acid on the surface of TiO 2 particles is shown in Figure . Under dark and dry conditions (Figure a), the peak at 1262 cm –1 could be associated with CO–H in-plane bend and the peaks at 1340 and 1372 cm –1 could be referred to as C–H in-plane bend. , The peaks at 1446, 1518, and 1560 cm –1 could be assigned to C–O stretching vibrations of the acrylate OCO group, while the peak at 1637 cm –1 belonged to surface-adsorbed water. , Peaks in the range of 1663–1725 cm –1 represent the CO of adsorbed acrylic acid. , The OCO symmetric stretching is observed at 2989 cm –1 , while 3045 and 3107 cm –1 could be assigned to the C–H in-plane bend and C–H stretch, respectively. , Infrared spectroscopy proves that acrylic acid could also occupy Lewis acid sites, Lewis basic sites, and OH sites on the surface of TiO 2 to form adsorbed acrylic acid and acrylate (Figure ) (R14–16). Moreover, the production of acrylate increased with reaction time and proved the formation of acrylate and surface adsorbed acrylic acid during the heterogeneous reactions (Figure d).…”

“…Under dark and dry conditions (Figure 3a), the peak at 1262 cm −1 could be associated with CO−H inplane bend and the peaks at 1340 and 1372 cm −1 could be referred to as C−H in-plane bend. 38,40 The peaks at 1446, 1518, and 1560 cm −1 could be assigned to C−O stretching vibrations of the acrylate OCO group, while the peak at 1637 cm −1 belonged to surface-adsorbed water. 38,40 Peaks in the range of 1663−1725 cm −1 represent the C�O of adsorbed acrylic acid.…”

“…38,40 The peaks at 1446, 1518, and 1560 cm −1 could be assigned to C−O stretching vibrations of the acrylate OCO group, while the peak at 1637 cm −1 belonged to surface-adsorbed water. 38,40 Peaks in the range of 1663−1725 cm −1 represent the C�O of adsorbed acrylic acid. 57,58 The OCO symmetric stretching is observed at 2989 cm −1 , while 3045 and 3107 cm −1 could be assigned to the C−H in-plane bend and C−H stretch, respectively.…”

“…Acrylic acid (C 3 H 4 O 2 ) is a representative unsaturated short chain fatty acid that can be emitted not only from the production plants of acrylate and some resin products but also from sheep rumen fluid and seaweed. − Grudzinskiĭ observed the concentration of acrylic acid in the factory plume to be about 22 to 183 mg m –3 . In addition, some studies have shown that the decomposition of dimethyl sulfoniopropionate in the ocean also produces acrylic acid. , Acrylic acid is widely used in the production of polymers and in the coating of some materials. , As one of the 189 hazardous air pollutants, gas-phase oxidation and liquid-phase radical reactions of acrylic acid have been studied to some extent. − The reaction rate constants of acrylic acid with OH radicals, Cl atoms, and ozone have been calculated, and the relevant reaction mechanisms have also been studied by experiments and theoretical calculations. ,− Moreover, the heterogeneous reaction of acrylic acid on the surface of mineral dust particles has also been studied. For example, Wu et al.…”

“…42,43 Acrylic acid is widely used in the production of polymers and in the coating of some materials. 38,44 As one of the 189 hazardous air pollutants, gas-phase oxidation and liquid-phase radical reactions of acrylic acid have been studied to some extent. 38−40 The reaction rate constants of acrylic acid with OH radicals, Cl atoms, and ozone have been calculated, and the relevant reaction mechanisms have also been studied by experiments and theoretical calculations.…”