Characterization of surface functional groups present on laboratory-generated and ambient aerosol particles by means of heterogeneous titration reactions

• Published in: Journal of aerosol science Vol. 40; no. 6; pp. 534 - 548
• Main Authors: Setyan, Ari, Sauvain, Jean-Jacques, Riediker, Michael, Guillemin, Michel, Rossi, Michel J.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01-06-2009; Elsevier
• Subjects: Aerosols; Chemistry; Colloidal state and disperse state; Exact sciences and technology; Field measurement; General and physical chemistry; Heterogeneous reaction; Knudsen flow reactor; Physical and chemical studies. Granulometry. Electrokinetic phenomena; PM 4; Surface reactivity; Switzerland; Europe; Field measurement; PM 4; Surface reactivity; Knudsen flow reactor; Heterogeneous reaction; Measurement; Basic site; Knudsen flow; Acidic site; Soot; Samplings; Laboratory; Ultrafine particle; Probe; Characterization; Particle; Fine particle; Sampling; Reactor; Chemical reactivity; Functional group; Bus; 1,8-p-Menthadiene; Reference; Carbonyl; Base; Gases; Acids; Chemical reaction; Filter; Aerosols; Technique; PM; Neutralization
• ISSN: 0021-8502; 1879-1964
• DOI: 10.1016/j.jaerosci.2009.01.008

A Knudsen flow reactor has been used to quantify surface functional groups on aerosols collected in the field. This technique is based on a heterogeneous titration reaction between a probe gas and a specific functional group on the particle surface. In the first part of this work, the reactivity of different probe gases on laboratory-generated aerosols (limonene SOA, Pb(NO
3)
2, Cd(NO
3)
2) and diesel reference soot (SRM 2975) has been studied. Five probe gases have been selected for the quantitative determination of important functional groups: N(CH
3)
3 (for the titration of acidic sites), NH
2OH (for carbonyl functions), CF
3COOH and HCl (for basic sites of different strength), and O
3 (for oxidizable groups). The second part describes a field campaign that has been undertaken in several bus depots in Switzerland, where ambient fine and ultrafine particles were collected on suitable filters and quantitatively investigated using the Knudsen flow reactor. Results point to important differences in the surface reactivity of ambient particles, depending on the sampling site and season. The particle surface appears to be multi-functional, with the simultaneous presence of antagonistic functional groups which do not undergo internal chemical reactions, such as acid–base neutralization. Results also indicate that the surface of ambient particles was characterized by a high density of carbonyl functions (reactivity towards NH
2OH probe in the range 0.26–6 formal molecular monolayers) and a low density of acidic sites (reactivity towards N(CH
3)
3 probe in the range 0.01–0.20 formal molecular monolayer). Kinetic parameters point to fast redox reactions (uptake coefficient
γ
0>10
−3 for O
3 probe) and slow acid–base reactions (
γ
0<10
−4 for N(CH
3)
3 probe) on the particle surface.