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Abstract. 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 (NO3) in modern OFRs to mimic nighttime oxidative aging processes has been limited due to the complexity of conventional techniques that are used to generate NO3.Here, we present a new method that uses a laminar flow reactor (LFR) to continuously generate dinitrogen pentoxide (N2O5) in the gas phase at room temperature from the NO2 + O3 and NO2 + NO3 reactions.The N2O5 is then injected into a dark Potential Aerosol Mass (PAM) OFR and decomposes to generate NO3; hereafter, this method is referred to as “OFR-iN2O5” (where “i” stands for “injected”).To assess the applicability of the OFR-iN2O5 method towards different chemical systems, we present experimental and model characterization of the integrated NO3 exposure, NO3:O3, NO2:NO3, and NO2:O2 as a function of LFR and OFR conditions.These parameters were used to investigate the fate of representative organic peroxy radicals (RO2) and aromatic alkyl radicals generated from volatile organic compound (VOC) + NO3 reactions, and VOCs that are reactive towards both O3 and NO3.Finally, we demonstrate the OFR-iN2O5 method by generating and characterizing secondary organic aerosol from the β-pinene + NO3 reaction.
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Technical note: Gas-phase nitrate radical generation via irradiation of aerated ceric ammonium nitrate mixtures
Abstract. We present a novel photolytic source of gas-phase NO3 suitable for use in atmospheric chemistry studies that has several advantages over traditional sources that utilize NO2 + O3 reactions and/or thermal dissociation of dinitrogen pentoxide (N2O5). The method generates NO3 via irradiation of aerated aqueous solutions of ceric ammonium nitrate (CAN, (NH4)2Ce(NO3)6) and nitric acid (HNO3) or sodium nitrate (NaNO3). We present experimental and model characterization of the NO3 formation potential of irradiated CAN / HNO3 and CAN / NaNO3 mixtures containing [CAN] = 10−3 to 1.0 M, [HNO3] = 1.0 to 6.0 M, [NaNO3] = 1.0 to 4.8 M, photon fluxes (I) ranging from 6.9 × 1014 to 1.0 × 1016 photons cm−2 s−1, and irradiation wavelengths ranging from 254 to 421 nm. NO3 mixing ratios ranging from parts per billion to parts per million by volume were achieved using this method. At the CAN solubility limit, maximum [NO3] was achieved using [HNO3] ≈ 3.0 to 6.0 M and UVA radiation (λmax = 369 nm) in CAN / HNO3 mixtures or [NaNO3] ≥ 1.0 M and UVC radiation (λmax = 254 nm) in CAN / NaNO3 mixtures. Other reactive nitrogen (NO2, N2O4, N2O5, N2O6, HNO2, HNO3, HNO4) and reactive oxygen (HO2, H2O2) species obtained from the irradiation of ceric nitrate mixtures were measured using a NOx analyzer and an iodide-adduct high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS). To assess the applicability of the method for studies of NO3-initiated oxidative aging processes, we generated and measured the chemical composition of oxygenated volatile organic compounds (OVOCs) and secondary organic aerosol (SOA) from the β-pinene + NO3 reaction using a Filter Inlet for Gases and AEROsols (FIGAERO) coupled to the HR-ToF-CIMS.
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- PAR ID:
- 10488842
- Publisher / Repository:
- EGU Publications
- Date Published:
- Journal Name:
- Atmospheric Chemistry and Physics
- Volume:
- 23
- Issue:
- 21
- ISSN:
- 1680-7324
- Page Range / eLocation ID:
- 13869 to 13882
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/acp-23-13869-2023
