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Near-surface tropospheric ozone depletion events (ODEs) occur in the polar regions during springtime when ozone reacts with bromine radicals, driving tropospheric ozone mole ratios below 15 ppb (part-per-billion; nmol mol−1). ODEs alter atmospheric oxidative capacity by influencing halogen radical recycling mechanisms and the photochemical production of hydroxyl radicals (˙OH). Herein, we examined five years of continuous ozone measurements at two coastal Arctic sites: Utqiaġvik, Alaska and ∼260 km southeast at Oliktok Point, within the North Slope of Alaska oil fields. These data informed seasonal ozone trends, springtime ozone depletion, and the influence of oil field combustion emissions. Ozone depletion occurred frequently during spring: 35% of the time at Utqiaġvik and 40% at Oliktok Point. ODEs often occurred concurrently at both sites (40–92% of observed ODEs per year), supporting spatially widespread ozone depletion. Observed ozone depletion timescales are consistent with transport of ozone-depleted air masses, suggesting regional active bromine chemistry. Local-scale ozone depletion affecting individual sites occurred less frequently. Ozone depletion typically coincided with calm winds and had no clear dependence on temperature. Consistently lower ozone mole ratios year-round at Oliktok Point, compared to Utqiaġvik, indicate local-scale ozone titration within the stable boundary layer by nitric oxide (NO˙) combustion emissions in the Arctic oil fields. Oxidation of combustion-derived volatile organic compounds in the presence of NOx also likely contributes to ozone formation downwind, for example at Utqiaġvik, pointing to complex local and regional impacts of combustion emissions as Arctic anthropogenic activity increases. 

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.