Articles | Volume 17, issue 18
Atmos. Chem. Phys., 17, 10919–10935, 2017
Atmos. Chem. Phys., 17, 10919–10935, 2017

Research article 15 Sep 2017

Research article | 15 Sep 2017

Long-term O3–precursor relationships in Hong Kong: field observation and model simulation

Yu Wang1,*, Hao Wang1,*, Hai Guo1, Xiaopu Lyu1, Hairong Cheng2, Zhenhao Ling3, Peter K. K. Louie4, Isobel J. Simpson5, Simone Meinardi5, and Donald R. Blake5 Yu Wang et al.
  • 1Air Quality Studies, Department of Civil and Environmental Engineering, the Hong Kong Polytechnic University, Hong Kong SAR, China
  • 2Department of Environmental Engineering, School of Resource and Environmental Sciences, Wuhan University, Wuhan 430079, China
  • 3School of Atmospheric Sciences, Sun Yat-sen University, Guangzhou, China
  • 4Air Group, Hong Kong Environmental Protection Department, Hong Kong SAR, China
  • 5Department of Chemistry, University of California, Irvine, CA, USA
  • *These authors contributed equally to this work.

Abstract. Over the past 10 years (2005–2014), ground-level O3 in Hong Kong has consistently increased in all seasons except winter, despite the yearly reduction of its precursors, i.e. nitrogen oxides (NOx =  NO + NO2), total volatile organic compounds (TVOCs), and carbon monoxide (CO). To explain the contradictory phenomena, an observation-based box model (OBM) coupled with CB05 mechanism was applied in order to understand the influence of both locally produced O3 and regional transport. The simulation of locally produced O3 showed an increasing trend in spring, a decreasing trend in autumn, and no changes in summer and winter. The O3 increase in spring was caused by the net effect of more rapid decrease in NO titration and unchanged TVOC reactivity despite decreased TVOC mixing ratios, while the decreased local O3 formation in autumn was mainly due to the reduction of aromatic VOC mixing ratios and the TVOC reactivity and much slower decrease in NO titration. However, the decreased in situ O3 formation in autumn was overridden by the regional contribution, resulting in elevated O3 observations. Furthermore, the OBM-derived relative incremental reactivity indicated that the O3 formation was VOC-limited in all seasons, and that the long-term O3 formation was more sensitive to VOCs and less to NOx and CO in the past 10 years. In addition, the OBM results found that the contributions of aromatics to O3 formation decreased in all seasons of these years, particularly in autumn, probably due to the effective control of solvent-related sources. In contrast, the contributions of alkenes increased, suggesting a continuing need to reduce traffic emissions. The findings provide updated information on photochemical pollution and its impact in Hong Kong.

Short summary
Though the Hong Kong government has made great efforts toward a reduction in emissions, ambient O3 levels have presented an increasing trend in the past decade. Data analysis and model simulations indicated that the locally produced O3 in Hong Kong varied by seasons, while regional transport from the PRD region made a substantial contribution to ambient O3 in Hong Kong and even increased in autumn. This long-term study has important implications for other Chinese cities to reduce O3 pollution.
Final-revised paper