Nitrate radical generation via continuous generation of dinitrogen pentoxide in a laminar flow reactor coupled to an oxidation flow reactor
Résumé
Oxidation flow reactors (OFRs) are an emerging tool for studying the formation and oxidative aging of organic aerosols and other applications. The majority of OFR studies to date have involved the generation of the hydroxyl radical (OH) to mimic daytime oxidative aging processes. In contrast, the use of the nitrate radical (NO 3) in modern OFRs to mimic nighttime oxidative aging processes has been limited due to the complexity of conventional techniques that are used to generate NO 3. Here, we present a new method that uses a laminar flow reactor (LFR) to continuously generate dinitrogen pentoxide (N 2 O 5) in the gas phase at room temperature from the NO 2 + O 3 and NO 2 + NO 3 reactions. The N 2 O 5 is then injected into a dark Potential Aerosol Mass (PAM) OFR and decomposes to generate NO 3 ; hereafter, this method is referred to as "OFR-iN 2 O 5 " (where "i" stands for "injected"). To assess the applicability of the OFR-iN 2 O 5 method towards different chemical systems, we present experimental and model characterization of the integrated NO 3 exposure, NO 3 : O 3 , NO 2 : NO 3 , and NO 2 : O 2 as a function of LFR and OFR conditions. These parameters were used to investigate the fate of representative organic peroxy radicals (RO 2) and aromatic alkyl radicals generated from volatile organic compound (VOC) + NO 3 reactions, and VOCs that are reactive towards both O 3 and NO 3. Finally, we demonstrate the OFR-iN 2 O 5 method by generating and characterizing secondary organic aerosol from the β-pinene + NO 3 reaction .
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