ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-6-8961-2006 Ozone production and hydrocarbon reactivity in Hong Kong, Southern China Zhang J. 1 2 Wang T. 3 Chameides W. L. 1 Cardelino C. 1 Kwok J. 3 Blake D. R. 4 Ding A. 3 So K. L. 3 School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USA School of Geography, Beijing Normal University, Beijing 100875, China Department of Civil and Structural Engineering, Hong Kong Polytechnic University, HongKong, China Department of Chemistry, University of California, Irvine, CA 92697, USA 25 09 2006 6 5 8961 9002 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys-discuss.net/6/8961/2006/acpd-6-8961-2006.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/6/8961/2006/acpd-6-8961-2006.pdf

Data obtained in Hong Kong during the Hong Kong and the Pearl River Delta (PRD) Pilot Air Monitoring Study in autumn 2002 are analyzed to unravel the relationship between ground-level ozone (O<sub>3</sub>), pollution precursors, and cross-border transport. Ten ozone episodes, during which the hourly O<sub>3</sub> concentration exceeded 100 ppbv in 9 cases and 90 ppbv in one case, are subject to detailed analysis, including one case with hourly O<sub>3</sub> of 203 ppbv, which is the highest concentration on record to date in Hong Kong. Combined with high-resolution back trajectories, dCO/dNO<sub><i>y</i></sub> is used to define whether O<sub>3</sub> is locally or regionally produced. Five out of the ten Hong Kong O<sub>3</sub>-episodes studied show a ''pollution signature'' that is indicative of impact from Guangdong Province. Examination of speciated volatile organic compounds (VOCs) shows that the reactivity of VOCs is dominated by anthropogenic VOCs, of which the reactive aromatics dominate, in particular xylenes and toluene. Calculations using a photochemical box model indicate that between 50&ndash;100% of the O<sub>3</sub> increase observed in Hong Kong during the O<sub>3</sub> episodes can be explained by photochemical generation within the Hong Kong area, provided that nitrous acid (HONO) is present at the concentrations derived from this study. An Observation-Based Model (OBM) is used to calculate the sensitivity of the O<sub>3</sub> production to changes in the concentrations of the precursor compounds. Generally the production of O<sub>3</sub> throughout much of the Hong Kong area is limited by VOCs, while high nitric oxide (NO) concentrations suppress O<sub>3</sub> concentration.