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Preprints
https://doi.org/10.5194/acp-2019-1012
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-1012
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

  16 Dec 2019

16 Dec 2019

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This preprint has been withdrawn by the authors.

The role of HONO in O3 formation and insight into its formation mechanism during the KORUS-AQ Campaign

Junsu Gil1, Jeonghwan Kim2, Meehye Lee1, Gangwoong Lee2, Dongsoo Lee3, Jinsang Jung4, Joonyeong An5, Jinkyu Hong6, Seogju Cho7, Jeonghoon Lee8, and Russell Long9 Junsu Gil et al.
  • 1Department of Earth and Environmental Sciecne, Korea University, Seoul, Korea
  • 2Department of Environmental Sciecne, Hankuk University of Foreign Studies, Yongin, Korea
  • 3Department of Chemistry, Yonsei University, Seoul, Korea
  • 4Korea Research Institute of Standards and Science (KRISS), Daejeon, Korea
  • 5National Institute of Environmental Research (NIER), Incheon, Korea
  • 6Department of Atmospheric Sciences, Yonsei University, Seoul, Korea
  • 7Seoul Research Institute of Public Health and Environment, Seoul, Korea
  • 8School of Mechanical Engineering, Korea University of Technology and Education, Cheonan, Korea
  • 9United States Environmental Protection Agency, Washington, USA

Abstract. Photolysis of nitrous acid (HONO) has long been recognized as an early morning source of OH radicals in urban air, but the detailed mechanism of its formation is still unclear. During the Korea-US Air Quality (KORUS-AQ) campaign, HONO was measured using Quantum Cascade Tunable Diode Laser Absorption Spectroscopy (QC-TDLAS) at Olympic Park in Seoul from 17 May to 10 June, 2016. HONO concentrations ranged from 0.07 ppbv to 3.46 ppbv with an average of 0.93 ppbv. HONO remained high at night from 1 am to 5 am, during which the mean concentration was higher in high-O3 episodes (1.82 ppbv) than non-episode (1.20 ppbv). In the morning, OH budget due to HONO photolysis were higher by 50 % (0.95 pptv) during high-O3 episodes compared to non-episode. Diurnal variations of HOx and O3 simulated by the F0AM model demonstrated a difference of ~ 20 ppbv in daily maximum O3 between the two periods. The HONO concentration increased with relative humidity (RH) until 80 %, of which the highest HONO was associated with the top 10 % NOx, confirming that NOx is a crucial precursor of HONO and its formation is facilitated by humidity. The conversion ratio of NOx to HONO was estimated to be 0.86 × 10−2 h−1 at night and also increased with RH. As surrogate for the catalyst surface, the mass concentrations of black carbon (eBC) and the surface areas of particles smaller than 120 nm showed a tendency for RH similar to conversion ratio. Using an Artificial Neuron Network (ANN) model, HONO concentrations were successfully simulated with measured variables (r = 0.8 for the best suite), among which NOx, surface area, and RH were found to be main factors affecting ambient HONO concentrations with weigh values of 26.2 %, 11.9 %, and 10.6 %, respectively. This study demonstrates the coupling of HONO with HOx-VOCs-O3 cycle in Seoul Metropolitan Areas (SMA) and provides practical evidence for heterogeneous formation of HONO by employing the ANN model to atmospheric chemistry.

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Junsu Gil et al.

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Junsu Gil et al.

Junsu Gil et al.

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Short summary
During the KORUS-AQ campaign, nitrous acid (HONO) concentrations in Seoul were higher in high-O3 episodes than non-episodes. The photochemical model simulation demonstrates the role of HONO in promoting O3 formation through OH production and subsequent VOCs oxidation. The ambient HONO concentrations were reasonably represented by an Artificial Neural Network model, highlighting NOx, surface area, and relative humidity as crucial parameters for HONO formation in Seoul under high NOx conditions.
During the KORUS-AQ campaign, nitrous acid (HONO) concentrations in Seoul were higher in high-O3...
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