References

ACP

Atmospheric Chemistry and Physics

ACP

1680-7324

Copernicus GmbH

Göttingen, Germany

10.5194/acp-10-7561-2010

Heterogeneous chemistry of monocarboxylic acids on α-Al2O3 at different relative humidities

Tong

S. R.

¹ Wu

L. Y.

¹ Ge

M. F.

¹ Wang

W. G.

¹ Pu

Z. F.

Beijing National Laboratory for Molecular Sciences (BNLMS), State Key Laboratory for Structural Chemistry of Unstable and Stable Species,Institute of Chemistry, Chinese Academy of Sciences, 100190, Beijing, China

16 08 2010

10 16 7561 7574

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A study of the atmospheric heterogeneous reactions of formic acid, acetic acid, and propionic acid on α-Al2O3 was performed at ambient condition by using a diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) reactor. From the analysis of the spectral features, observations of carboxylates formation provide strong evidence for an efficient reactive uptake process. Comparison of the calculated and experimental vibrational frequencies of adsorbed carboxylates establishes the bridging coordinated structures on the surface. The uptake coefficients of formic acid, acetic acid, and propionic acid on α-Al2O3 particles are (2.07±0.26)×10−3 or (2.37±0.30) ×10−7, (5.00±0.69)×10−3 or (5.99±0.78)×10−7, and (3.04±0.63)×10−3 or (3.03±0.52)×10−7, respectively (using geometric or BET surface area). Furthermore, the effect of varying relative humidity (RH) on these heterogeneous reactions was studied. The uptake coefficients of monocarboxylic acids on α-Al2O3 particles increase initially (RH<20%) and then decrease with the increased RH (RH>20%) which was due to the effect of water on carboxylic acid solvation, particle surface hydroxylation, and competition for reactive sites. On the basis of the results of experimental simulation, the mechanism of heterogeneous reaction of α-Al2O3 with carboxylic acids at ambient RH was discussed. The loss of atmospheric monocarboxylic acids due to reactive uptake on available mineral dust particles may be competitive with homogeneous loss pathways, especially in dusty urban and desertified environments.

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