Investigating the gas-phase reaction mechanism of catechol with ozone: Product analysis and insights

Abstract

Volatile aromatic compounds (VOCs) are ubiquitous in the environment, they can be emitted from biogenic and anthropogenic sources. They can contribute to the formation of many products leading to the formation of secondary organic aerosols (SOA). The products of the gas phase reaction of 1,2-benzenediol (catechol) with ozone were studied in a simulation chamber at atmospheric pressure and 294 ± 2 K in presence of different levels of relative humidity (0–60%). The gas phase products were monitored continuously by a PTR-ToF-MS for 2 h, whereas filters samples were collected directly from the reaction chamber and analyzed by thermo-desorption gas chromatography; TD-GC-MS. This study shows the different potential chemical pathways that catechol could follow to form a variety of products under dry, low and high humidity conditions. The molecular mass 98 was found to be distinctive and appears in the gas phase when humidity in the reaction chamber is between 20 and 60%. Other new masses (m/z) such as 176, 154, 116, 68, 72, 80, 96, 108, and 124 were also detected under different experimental conditions. Furthermore, the catechol concentration has been monitored continuously by a PTR-ToF-MS from low to high humidity conditions (RH = 7.5−78.8%). The purpose of the latter is to suggest that the formation of catechol-H2O clusters occurs in the gas phase of the reaction chamber causing a decrease in catechol reactivity towards ozone and other gases and subsequently a decrease in the rate constant.