HO$_x$ and NO$_x$ production in oxidation flow reactors via photolysis of isopropyl nitrite, isopropyl nitrite-d$_7$, and 1,3-propyl dinitrite at λ = 254, 350, and 369 nm

Abstract

Oxidation flow reactors (OFRs) are an emerging technique for studying the formation and oxidative aging of organic aerosols and other applications. In these flow reac- tors, hydroxyl radicals (OH), hydroperoxyl radicals (HO$_2$), and nitric oxide (NO) are typically produced in the follow- ing ways: photolysis of ozone (O$_3$) at λ = 254 nm, photoly- sis of H$_2$O at λ = 185 nm, and via reactions of O(1D) with H2 O and nitrous oxide (N$_2$O); O($^1$D) is formed via photolysis of O$_3$ at λ=254nm and/or N$_2$O at λ=185nm. Here, we adapt a complementary method that uses alkyl nitrite pho- tolysis as a source of OH via its production of HO$_2$ and NO followed by the reaction NO + HO$_2$ → NO$_2$ + OH. We present experimental and model characterization of the OH exposure and NOx levels generated via photolysis of C$_3$ alkyl nitrites (isopropyl nitrite, perdeuterated isopropyl nitrite, 1,3- propyl dinitrite) in the Potential Aerosol Mass (PAM) OFR as a function of photolysis wavelength (λ = 254 to 369 nm) and organic nitrite concentration (0.5 to 20 ppm). We also apply this technique in conjunction with chemical ionization mass spectrometer measurements of multifunctional oxida- tion products generated following the exposure of α-Pinene to HOx and NOx obtained using both isopropyl nitrite and O$_3$ + H$_2$O + N2O as the radical precursors.