Heterogeneous interaction of SiO2with N2O5: Aerosol flow tube and single particle optical levitation-Raman spectroscopy studies

M. J. Tang, J. C J Camp, L. Rkiouak, J. McGregor, I. M. Watson, R. A. Cox, M. Kalberer*, A. D. Ward, F. D. Pope

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)

18 Citations (Scopus)

Abstract

Silica (SiO2) is an important mineral present in atmospheric mineral dust particles, and the heterogeneous reaction of N2O5on atmospheric aerosol is one of the major pathways to remove nitrogen oxides from the atmosphere. The heterogeneous reaction of N2O5with SiO2has only been investigated by two studies previously, and the reported uptake coefficients differ by a factor of >10. In this work two complementary laboratory techniques were used to study the heterogeneous reaction of SiO2particles with N2O5at room temperature and at different relative humidities (RHs). The uptake coefficients of N2O5, γ(N2O5), were determined to be (7.2 ± 0.6) × 10-3(1σ) at 7% RH and (5.3 ± 0.8) × 10-3(1σ) at 40% RH for SiO2particles, using the aerosol flow tube technique. We show that γ(N2O5) determined in this work can be reconciled with the two previous studies by accounting for the difference in geometric and BET derived aerosol surface areas. To probe the particle phase chemistry, individual micrometer sized SiO2particles were optically levitated and exposed to a continuous flow of N2O5at different RHs, and the composition of levitated particles was monitored online using Raman spectroscopy. This study represents the first investigation into the heterogeneous reactions of levitated individual SiO2particles as a surrogate for mineral dust. Relative humidity was found to play a critical role: while no significant change of particle composition was observed by Raman spectroscopy during exposure to N2O5at RH of 3between the gas and adsorbed phases. The atmospheric implications of this work are discussed.

Original languageEnglish
Pages (from-to)8817-8827
Number of pages11
JournalJournal of Physical Chemistry A
Volume118
Issue number38
DOIs
Publication statusPublished - 25 Sep 2014

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    Tang, M. J., Camp, J. C. J., Rkiouak, L., McGregor, J., Watson, I. M., Cox, R. A., Kalberer, M., Ward, A. D., & Pope, F. D. (2014). Heterogeneous interaction of SiO2with N2O5: Aerosol flow tube and single particle optical levitation-Raman spectroscopy studies. Journal of Physical Chemistry A, 118(38), 8817-8827. https://doi.org/10.1021/jp506753c