Elevated levels of OH observed in haze events during wintertime in central Beijing

Research output: Contribution to journalArticlepeer-review

Authors

  • Eloise J. Slater
  • Lisa K. Whalley
  • Robert Woodward-Massey
  • Chunxiang Ye
  • James D. Lee
  • Freya Squires
  • James R. Hopkins
  • Rachel E. Dunmore
  • Marvin Shaw
  • Jacqueline F. Hamilton
  • Alastair R. Lewis
  • Tuan Vu
  • Yele Sun
  • Weiqi Xu
  • Siyao Yue
  • Lujie Ren
  • W. Joe
  • C. Nicholas Hewitt
  • Xinming Wang
  • Pingqing Fu
  • Dwayne E. Heard

Colleges, School and Institutes

External organisations

  • University of Leeds
  • Peking University
  • University of York
  • York University
  • Birmingham University
  • Institute of Atmospheric Physics Chinese Academy of Sciences
  • Lancaster Environment Centre
  • Guangzhou Institute of Geochemistry Chinese Academy of Sciences
  • Tianjin University

Abstract

Wintertime in situ measurements of OH, HO2 and RO2 radicals and OH reactivity were made in central Beijing during November and December 2016. Exceptionally elevated NO was observed on occasions, up to 250 ppbv. The daily maximum mixing ratios for radical species varied significantly day-To-day over the ranges 1 8106 cm 3 (OH), 0.2 1:5108 cm 3 (HO2) and 0.3 2:5108 cm 3 (RO2). Averaged over the full observation period, the mean daytime peak in radicals was 2:7106, 0:39108 and 0:88 108 cm 3 for OH, HO2 and total RO2, respectively. The main daytime source of new radicals via initiation processes (primary production) was the photolysis of HONO (83 %), and the dominant termination pathways were the reactions of OH with NO and NO2, particularly under polluted haze conditions. The Master Chemical Mechanism (MCM) v3.3.1 operating within a box model was used to simulate the concentrations of OH, HO2 and RO2. The model underpredicted OH, HO2 and RO2, especially when NO mixing ratios were high (above 6 ppbv). The observation-To-model ratio of OH, HO2 and RO2 increased from 1 (for all radicals) at 3 ppbv of NO to a factor of 3, 20 and 91 for OH, HO2 and RO2, respectively, at 200 ppbv of NO. The significant underprediction of radical concentrations by the MCM suggests a deficiency in the representation of gas-phase chemistry at high NOx . The OH concentrations were surprisingly similar (within 20% during the day) in and outside of haze events, despite j(O1D) decreasing by 50% during haze periods. These observations provide strong evidence that gasphase oxidation by OH can continue to generate secondary pollutants even under high-pollution episodes, despite the reduction in photolysis rates within haze.

Bibliographic note

Funding Information: Financial support. This research has been supported by the Nat- Publisher Copyright: © 2020 BMJ Publishing Group. All rights reserved. Copyright: Copyright 2020 Elsevier B.V., All rights reserved.

Details

Original languageEnglish
Article number14847
Pages (from-to)14847-14871
Number of pages25
JournalAtmospheric Chemistry and Physics
Volume20
Issue number23
Publication statusPublished - 2 Dec 2020

ASJC Scopus subject areas