Quantifying the reactive uptake of OH by organic aerosols in a continuous flow stirred tank reactor

Abstract

Here we report a new method for measuring the heterogeneous chemistry of sub-micron organic aerosol particles using a continuous flow stirred tank reactor. This approach is designed to quantify the real time heterogeneous kinetics, using a relative rate method, under conditions of low oxidant concentration and long reaction times that more closely mimic the real atmosphere than the conditions used in a typical flow tube reactor. A general analytical expression, which couples the aerosol chemistry with the flow dynamics in the chamber is developed and applied to the heterogeneous oxidation of squalane particles by hydroxyl radicals (OH) in the presence of O₂. The particle phase reaction is monitored via photoionization aerosol mass spectrometry and yields a reactive uptake coefficient of 0.51 ± 0.10, using OH concentrations of 1–7 × 10⁸ molecule cm⁻³ and reaction times of 1.5–3 h. In general, this approach provides a new way to connect the chemical aging of organic particles measured at short reaction times and high oxidant concentrations in flow tubes with the long reaction times and low oxidant conditions in smog chambers and the real atmosphere.