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Volume 16, issue 13
Atmos. Chem. Phys., 16, 8081–8093, 2016
https://doi.org/10.5194/acp-16-8081-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 16, 8081–8093, 2016
https://doi.org/10.5194/acp-16-8081-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 04 Jul 2016

Research article | 04 Jul 2016

Heterogeneous reactions of NO2 with CaCO3–(NH4)2SO4 mixtures at different relative humidities

Fang Tan1,2,*, Shengrui Tong1,*, Bo Jing1, Siqi Hou1,2, Qifan Liu1,2, Kun Li1,2, Ying Zhang1,2, and Maofa Ge1,2 Fang Tan et al.
  • 1State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
  • 2University of Chinese Academy of Sciences, Beijing 100049, China
  • *These authors contributed equally to this work.

Abstract. In this work, the heterogeneous reactions of NO2 with CaCO3–(NH4)2SO4 mixtures with a series of weight percentage (wt %) of (NH4)2SO4 were investigated using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) at different relative humidity (RH) values. For comparison, the heterogeneous reactions of NO2 with pure CaCO3 particles and pure (NH4)2SO4 particles, as well as the reaction of CaCO3 with (NH4)2SO4 particles, were also studied. The results indicated that NO2 did not show any significant uptake on (NH4)2SO4 particles, and it reacted with CaCO3 particles to form calcium nitrate under both dry and wet conditions. The heterogeneous reactions of NO2 with CaCO3–(NH4)2SO4 mixtures were markedly dependent on RH. Calcium nitrate was formed from the heterogeneous reactions at all the RHs investigated, whereas CaSO4  ⋅  0.5H2O (bassanite), CaSO4  ⋅  2H2O (gypsum), and (NH4)2Ca(SO4)2  ⋅  H2O (koktaite) were produced depending on RH. Under the dry condition, the heterogeneous uptake of NO2 on the mixtures was similar to that on CaCO3 particles with neglectable effects from (NH4)2SO4; the duration of initial stages and the NO3 mass concentrations had a negative linear relation with the mass fraction of (NH4)2SO4 in the mixtures. Under wet conditions, the chemical interaction of (NH4)2SO4 with Ca(NO3)2 enhances the nitrate formation, especially at medium RHs, while the coagulation of (NH4)2SO4 with CaCO3 exhibits an increasing inhibiting effects with increasing RH at the same time. In addition, the heterogeneous uptake of NO2 on the mixtures of CaCO3 and (NH4)2SO4 was found to favor the formation of bassanite and gypsum due to the decomposition of CaCO3 and the coagulation of Ca2+ and SO42−. A possible reaction mechanism was proposed and the atmospheric implications were discussed.

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The heterogeneous reactions of NO2 with CaCO3–(NH4)2SO4 mixtures were markedly dependent on RH. Calcium nitrate was formed under both dry and wet conditions; bassanite, gypsum, and koktaite were produced depending on RH. The heterogeneous uptake of NO2 on the CaCO3–(NH4)2SO4 mixtures was similar to that on pure CaCO3 particles under the dry condition, whereas the mixtures exhibited a promotive effect on the heterogeneous uptake of NO2 and the formation of nitrate, especially at medium RHs.
The heterogeneous reactions of NO2 with CaCO3–(NH4)2SO4 mixtures were markedly dependent on RH....
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