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

Atmospheric chemistry and physics

article

Slater, Eloise J.¹  Hamilton, Jacqueline F.²  Lewis, Alastair C.³  Crilley, Leigh R.⁴  Kramer, Louisa⁴  Bloss, William⁴  Vu, Tuan⁴  Sun, Yele⁶  Xu, Weiqi⁶  Yue, Siyao⁶  Ren, Lujie⁶  Whalley, Lisa K.¹  Acton, W. Joe F.⁸  Hewitt, C. Nicholas⁸  Wang, Xinming⁹  Fu, Pingqing^1,10  Heard, Dwayne E.¹  Woodward-Massey, Robert¹  Ye, Chunxiang¹  Lee, James D.³  Squires, Freya²  Hopkins, James R.³  Dunmore, Rachel E.²  Shaw, Marvin³ 

[1]School of Chemistry, University of Leeds

[2]Wolfson Atmospheric Chemistry Laboratories, Department of Chemistry, University of York

[3]National Centre for Atmospheric Science, University of York

[4]School of Geography, Earth and Environmental Sciences, University of Birmingham

[5]now at: Department of Chemistry, Faculty of Science, York University

[6]State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences

[7]National Centre for Atmospheric Science, University of Leeds

[8]Lancaster Environment Centre, Lancaster University

[9]State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences

[10]Institute of Surface-Earth System Science, Tianjin University

[11]now at: College of Environmental Sciences and Engineering, Peking University

DOI  :  10.5194/acp-20-14847-2020

学科分类：医学（综合）

来源: Copernicus Publications

【 摘 要 】

Wintertime in situ measurements of OH, HO 2 and RO 2 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– 8×10 6   cm −3 (OH), 0.2– 1.5×10 8   cm −3 ( HO 2 ) and 0.3– 2.5×10 8   cm −3 ( RO 2 ). Averaged over the full observation period, the mean daytime peak in radicals was 2.7×10 6 , 0.39×10 8 and 0.88×10 8   cm −3 for OH, HO 2 and total RO 2 , 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 NO 2 , 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, HO 2 and RO 2 . The model underpredicted OH, HO 2 and RO 2 , especially when NO mixing ratios were high (above 6  ppbv ). The observation-to-model ratio of OH, HO 2 and RO 2 increased from ∼1 (for all radicals) at 3  ppbv of NO to a factor of ∼3 , ∼20 and ∼91 for OH, HO 2 and RO 2 , 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 NO x . The OH concentrations were surprisingly similar (within 20 % during the day) in and outside of haze events, despite j ( O 1 D ) decreasing by 50 % during haze periods. These observations provide strong evidence that gas-phase oxidation by OH can continue to generate secondary pollutants even under high-pollution episodes, despite the reduction in photolysis rates within haze.

【 授权许可】

CC BY