A laboratory study of the heterogeneous reaction of nitric acid on calcium carbonate particles

Abstract

Abstract. It has been postulated that the reaction of nitric acid with calcium carbonate, namely, CaCO3(s) + 2HNO3(g) -0 Ca(NO3)2(s) + CO2(g) + H20(g), plays an important role in the atmosphere. In this study, transmission FTIR spectroscopy, diffuse reflectance UV-visible spectroscopy, transmission electron microscopy and a Knudsen cell reactor coupled to a quadrupole mass spectrometer have been used to investigate the heterogeneous reactivity of HNO3 on CaCO3 at 295 K as a function of relative humidity. Transmission FTIR spectroscopy was used to probe both gas-phase and adsorbed products and showed that the reaction of HNO3 and CaCO3 is limited to the surface of the CaCO3 particle in the absence of adsorbed water. However, in the presence of water vapor, the reaction is greatly enhanced and is not limited to the surface of the particle producing both solid calcium nitrate and gaseous carbon dioxide. The enhanced reactivity of the particles is attributed to the presence of a layer of adsorbed water on the particle surface. The amount of adsorbed water on the particle surface is strongly dependent on the extent of the reaction. This can be understood in terms of the increased hydrophilicity of calcium nitrate as compared to calcium carbonate. Data from experiments using a mass-calibrated Knudsen cell reactor showed the stoichiometry for the reaction determined from gas-phase species deviated from that expected from the balanced equation. Water adsorption on the particle surface and gases dissolved into the water layer appear to be the cause of this discrepancy. The measured uptake coefficient accounting for the BET area of the sample is determined to be 2.5 + 0.1 x 10 -4 for HNO3 on CaCO3 under dry conditions and is found to increase in the presence of water vapor. Atmospheric implications of the results presented here are discussed. This current laboratory study is motivated by the above modeling studies. Here we attempt to discern whether mineral aerosols containing CaCO3 would be a sufficient sink for HNO3 that could reduce the HNO3 to NO• ratio in the atmosphere. The following issues concerning the heterogeneous reactivity of HNO3 on CaCO3 particles are addressed in this study:(1) does nitric acid react with CaCO3 according to reaction (1)?; (2) is the reaction of nitric acid limited to the surface of the CaCO3 particles?; (3) does water adsorbed on the particle surface play a key role in the reaction?; (4) do the physicochemical properties of the particle change after reaction with HNO37; (5) is the reaction 29,053

Atmospheric measurements of gas-phase HNO<sub>3</sub> and SO<sub>2</sub> using chemical ionization mass spectrometry during the MINATROC field campaign 2000 on Monte Cimone

“…Observations by Galy-Lacaux and Modi (1998), in the Sahelian region during the wet season have demonstrated that the alkalinity of the dust particles favors the uptake of nitrogen-containing compounds, especially HNO 3 . Laboratory studies of Goodman et al (2000), have confirmed that HNO 3 removal by CaCO 3 particles could be significant in the atmosphere, as has been suggested by Dentener et al (1996), and Tabazedeh et al (1998). The importance of heterogeneous reactions of HNO 3 on mineral dust has been further supported by a combined laboratory and modeling study of Underwood et al (2001), who have shown that under conditions of high mineral-dust loadings and/or smaller size distributions the importance of these reactions is expected to increase.…”

Impact of mineral dust on nitrate, sulfate, and ozone in transpacific Asian pollution plumes

“…Uptake of HNO 3 takes place by acidbase titration on surface sites for dry dust, or in solution with adsorbed water (Goodman et al, 2000). Uptake of SO 2 is thought to take place by aqueous-phase oxidation of SO 2− 3 by O 3 (Ullerstam et al, 2002).…”

Impact of Gobi desert dust on aerosol chemistry of Xi'an, inland China during spring 2009: differences in composition and size distribution between the urban ground surface and the mountain atmosphere

“…Ca(NO 3 ) 2 is hydrophilic and fine particulate Ca(NO 3 ) 2 can deliquescence above ∼ 10 % relative humidity (Tobo et al, 2010). During the dust storm period, the fast formed Ca(NO 3 ) 2 can form a liquid film on the dust surface, which further promotes formation of nitric acid on the liquid phase by hydrolysis of other nitrogen oxides like N 2 O 5 (He et al, 2012;Pathak et al, 2009) and adsorption of gaseous HNO 3 (Goodman et al, 2000). Such a positive feedback resulted in a significant formation of NO − 3 even in the dry condition of the dust storm period.…”