Abstract
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 reactors, hydroxyl radicals (OH), hydroperoxyl radicals (HO2), and nitric oxide (NO) are typically produced in the following ways: photolysis of ozone (O3) at λ=254 nm, photolysis of H2O at λ=185 nm, and via reactions of O(1D) with H2O and nitrous oxide (N2O); O(1D) is formed via photolysis of O3 at λ=254 nm and/or N2O at λ=185 nm. Here, we adapt a complementary method that uses alkyl nitrite photolysis as a source of OH via its production of HO2 and NO followed by the reaction NO + HO2 → NO2 + OH. We present experimental and model characterization of the OH exposure and NOx levels generated via photolysis of C3 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 oxidation products generated following the exposure of α-Pinene to HOx and NOx obtained using both isopropyl nitrite and O3 + H2O + N2O as the radical precursors.
Highlights
Hydroxyl (OH) radicals govern the concentrations of most atmospheric organic compounds, including those that lead to secondary organic aerosol (SOA) formation
Potential limitations of the method include (1) the inability to unambiguously deconvolve contributions from multiple oxidants (O3, OH, NO3), which may compete with each other under certain conditions and for specific unsaturated precursors; (2) required use of 254 nm photolysis, which may enhance photolytic losses that compete with OH oxidation, especially for species that are characterized by strong absorption/quantum yield at 254 nm and low-OH reactivity (Peng et al, 2016); (3) optimal high-NOx application at OH exposures corresponding to multiple equivalent days of oxidative aging rather than 1 day or less
We compared nitric oxide (NO)−3 -Chemical ionization mass spectrometer (CIMS) spectra of photooxidation products generated from reaction of α-Pinene with radicals produced via alkyl nitrite photolysis and O(1D) + H2O + N2O reactions. 3.1 OH exposure (OHexp) and NOx generated from iPrONO
Summary
Hydroxyl (OH) radicals govern the concentrations of most atmospheric organic compounds, including those that lead to secondary organic aerosol (SOA) formation. Recent application of O(1D) + H2O + N2O reactions to study NOxdependent SOA formation pathways facilitated characterization of oxidation products generated over a range of low- to high-NOx conditions (Lambe et al, 2017; Peng et al, 2018). Potential limitations of the method include (1) the inability to unambiguously deconvolve contributions from multiple oxidants (O3, OH, NO3), which may compete with each other under certain conditions and for specific unsaturated precursors; (2) required use of 254 nm photolysis, which may enhance photolytic losses that compete with OH oxidation, especially for species that are characterized by strong absorption/quantum yield at 254 nm and low-OH reactivity (Peng et al, 2016); (3) optimal high-NOx application at OH exposures corresponding to multiple equivalent days of oxidative aging rather than 1 day or less. We carried out chemical ionization mass spectrometer measurements to compare nitrogen-containing photooxidation products obtained from the reaction of α-Pinene with radicals generated via alkyl nitrite photolysis or the O(1D) + H2O + N2O reaction
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
