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Updated: Jun 12, 2026

Flame Experiments at the Advanced Light Source: New Insights into Soot Formation Processes
Published on: May 26, 2014
Heterogeneous reaction of NO(2) on fresh and coated soot surfaces
Alexei F Khalizov1, Miguel Cruz-Quinones, Renyi Zhang
1Department of Atmospheric Sciences, Texas A&M University, College Station, Texas 77843, USA.
Abstract:
The heterogeneous reaction of nitrogen dioxide (NO(2)) on fresh and coated soot surfaces has been investigated to assess its role in night-time formation of nitrous acid (HONO) in the atmosphere. Soot surfaces were prepared by incomplete combustion of propane and kerosene fuels under lean and rich flame conditions and then processed by heating to evaporate semivolatile species or by coating with pyrene, sulfuric acid, or glutaric acid. Uptake kinetics and HONO yield measurements were performed in a low-pressure fast-flow reactor coupled to a chemical ionization mass spectrometer (CIMS), using atmospheric-level NO(2) concentrations. The uptake coefficient and the HONO yield upon interaction of NO(2) with nascent soot depend on the type of fuel and combustion regime and are the highest for samples prepared using fuel rich flame. Heating the nascent soot samples before exposure to NO(2) removes the organic material from the soot backbone, leading to a significant increase in NO(2) uptake coefficient and HONO yield. Continuous exposure to NO(2) reduces the reactivity of soot because of irreversible deactivation of the surface sites. Our results support the oxidation-reduction mechanism involving adsorptive and reactive centers on soot surface where NO(2) is converted to HONO and other products. Coating of the soot surface by different materials to simulate atmospheric aging has a strong impact on its reactivity toward NO(2) and the resulting HONO production. Coating of pyrene has little effect on either reaction rate or HONO yield. Sulfuric acid coating does not alter the uptake coefficient, but significantly reduces the amount of HONO formed. Coating of glutaric acid significantly increases NO(2) uptake coefficient and HONO yield. The results of our study indicate that the reactivity and HONO generating capacity of internally mixed soot aerosol will depend on the chemical composition of the coating material and hence will vary considerably in different polluted environments.
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