A Novel Flow Tube Method for Measuring Gas-Phase Reactions Kinetics and Uptake on Solid Surfaces: Application to Organic Peroxy Radical

Organic peroxy radicals (ROO^•) are critical intermediates in atmospheric chemistry, yet their interactions with solid surfaces remain poorly understood due to challenges in monitoring these reactive species. We present a new experimental flow tube setup designed to overcome these limitations, enabling direct measurement of the uptake of ROO^• on solid surfaces.

In our approach, ROO^• (specifically CH₃OO^• and 1-C₃H₇OO^•) are generated photolytically and introduced into reaction tubes composed of, or filled with, various materials. The system is coupled with a Proton-Transfer-Reaction Time-of-Flight Mass Spectrometer (PTR-TOF-MS), allowing direct detection of ROO^•. Reaction kinetics are determined by varying the residence time in the reactor tube, achieved either by adjusting the tube length or changing the gas flow rate.

Using this method, we successfully monitored the uptake of CH₃OO^• and 1-C₃H₇OO^• on solid surfaces and identified reaction products. Results shown that the ROO^• uptake is highly dependent on the surface material. Non-conductive materials such as borosilicate glass and perfluoroalkoxy alkane (PFA) showed negligible uptake, whereas metallic surfaces exhibited significant reactivity. A second study examined atmospherically relevant inorganic salts. 

Our findings highlight the pivotal role of material redox properties in driving the surface reactivity of organic peroxy radicals, providing new insights into their fundamental behavior and raising new questions about their role in atmospheric environments.