ACP Atmospheric Chemistry and Physics ACP Atmos. Chem. Phys. 1680-7324 Copernicus Publications Göttingen, Germany 10.5194/acp-13-3881-2013 Characterization of photochemical pollution at different elevations in mountainous areas in Hong Kong Guo H. https://orcid.org/0000-0002-7996-7294 1 Ling Z. H. 1 Cheung K. 1 Jiang F. 2 Wang D. W. 1 Simpson I. J. 3 Barletta B. 3 Meinardi S. 3 Wang T. J. 4 Wang X. M. 5 Saunders S. M. 6 Blake D. R. 3 Air Quality Studies, Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong, China International Institute for Earth System Science, Nanjing University, Nanjing, China Department of Chemistry, University of California at Irvine, California, USA School of Atmospheric Sciences, Nanjing University, Nanjing, China Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China School of Biomedical, Biomolecular and Chemical Sciences, University of Western Australia, Perth, Australia 16 04 2013 13 8 3881 3898 Copyright: © 2013 H. Guo et al. 2013 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://acp.copernicus.org/articles/13/3881/2013/acp-13-3881-2013.html The full text article is available as a PDF file from https://acp.copernicus.org/articles/13/3881/2013/acp-13-3881-2013.pdf

To advance our understanding on the factors that affect photochemical pollution at different elevations in mountainous areas, concurrent systematic field measurements (September to November 2010) were conducted at a mountain site and at an urban site at the foot of the mountain in Hong Kong. The mixing ratios of air pollutants were greater at the foot of the mountain (i.e., Tsuen Wan urban site, TW) than near the summit (i.e., Tai Mao Shan mountain site, TMS), expect for ozone. In total, only one O<sub>3</sub> episode day was observed at TW, whereas twenty-one (21) O<sub>3</sub> episode days were observed at TMS. The discrepancy of O<sub>3</sub> at the two sites was attributed to the mixed effects of NO titration, vertical meteorological conditions, regional transport and mesoscale circulations. The lower NO levels at TMS and the smaller differences of "oxidant" O<sub>x</sub> (O<sub>3</sub> + NO<sub>2</sub>) between the two sites suggested that variations of O<sub>3</sub> at the two sites were partly attributed to different degree of NO titration. In addition, analysis of vertical structure of meteorological variables revealed that the inversion layer at the range of altitudes of 500–1000 m might be another factor that caused the high O<sub>3</sub> levels at TMS. Furthermore, analyses of the wind fields, the levels of air pollutants in different air flows, ratios of different trace gases and the correlation between variability and the lifetime of VOCs (volatile organic compounds) indicated that high O<sub>3</sub> concentrations at TMS were somewhat influenced by regional air masses from the highly polluted Pearl River delta (PRD) region. In particular, the diurnal profiles and correlations of gaseous pollutants suggested influence of mesoscale circulations, which is confirmed using the Master Chemical Mechanism moving box model (Mbox) and the Weather Research and Forecasting (WRF) model. By investigating the correlations of observed O<sub>3</sub> and NO<sub>x</sub>* and the relationships of O<sub>3</sub> and its precursors by an observation-based model (OBM), as well as the ratios of VOC/NO<sub>x</sub>, it was concluded that photochemical O<sub>3</sub> formation at TMS was mostly influenced by VOCs, with measurable impact of NO<sub>x</sub>, while O<sub>3</sub> production at TW was generally limited by the concentrations of VOCs. This is the first report of the comprehensive analysis on the data of photochemical pollution obtained from concurrent measurements in mountainous areas in the PRD region.

 References AFCD (Agriculture, Fisheries and conservation Department), available at: <a href="http://www.afcd.gov.hk/">http://www.afcd.gov.hk/</a>, 2008. Atkinson, R.: Gas-phase tropospheric chemistry of volatile organic compounds: 1. Alkanes and alkenes, J. Phys. Chem. Ref. Data, 26, 215–290, 1997. Barletta, B., Meinardi, S., Simpson, I. J., Zou, S. C., Rowland, F. S., and Blake, D. R.: Ambient mixing ratios of nonmethane hydrocarbons (NMHCs) in two major urban centers of the Pearl River Delta (PRD) region: Guangzhou and Dongguan, Atmos. Environ., 42, 4393–4408, 2008. Bloss, C., Wagner, V., Jenkin, M. E., Volkamer, R., Bloss, W. J., Lee, J. D., Heard, D. E., Wirtz, K., Martin-Reviejo, M., Rea, G., Wenger, J. C., and Pilling, M. J.: Development of a detailed chemical mechanism (MCMv3.1) for the atmospheric oxidation of aromatic hydrocarbons, Atmos. Chem. Phys., 5, 641–664, <a href="http://dx.doi.org/10.5194/acp-5-641-2005">https://doi.org/10.5194/acp-5-641-2005</a>, 2005. Burley, J. D. and Bytnerowicz, A.: Surface ozone in the white mountains of California, Atmos. Environ., 45, 4591–4602, 2011. Cardelino, C. A. and Chameides, W. L.: An observation-based model for analyzing ozone precursor relationships in the urban atmosphere, J. Air Waste Manage., 45, 161–180, 1995. Chameides, W. L. and Demerjian, K. L.: An Assessment of Tropospheric Ozone Pollution: a North America Perspective, Palo Alto, California, USA, 2000. Chan, C. Y. and Chan, L. Y.: Effect of meteorology and air pollutant transport on ozone episodes at a subtropical coastal Asian city, Hong Kong, J. Geophys. Res., 105, 20707–20724, 2000. Chan, L. Y., Chan, C. Y., and Qin, Y.: Surface ozone pattern in Hong Kong, J. Appl. Meteorol., 37, 1153–1165, 1998a. Chan, L. Y., Liu, H. Y., and Lam, K. S.: Analysis of the seasonal behavior of tropospheric ozone at Hong Kong, Atmos. Environ., 32, 159–168, 1998b. Chen, C. L., Tsuang, B. J., Tu, C. Y., Cheng, W. L., and Lin, W. D.: Wintertime vertical profiles of air pollutants over a suburban area in central Taiwan, Atmos. Environ., 36, 2049–2059, 2002. Chen, F. and Dudhia, J.: Coupling an Advanced Land Surface-Hydrology Model with the Penn State-NCAR MM5 Modeling System. Part I: Model implementation and sensitivity, Mon. Weathrt Rev., 129, 569–585, 2001. Cheng, H. R., Guo, H., Wang, X. M., Saunders, S. M., Lam, S. H. M., Jiang, F., Wang, T., Ding, A., Lee, S., and Ho, K. F.: On the relationship between ozone and its precursors in the Pearl River Delta: application of an observation-based model (OBM), Environ. Sci. Pollut. Res., 17, 547–560, 2010. Chou, C. C. K., Liu, S. C., Lin, C. Y., Shiu, C. J., and Chang, K. H.: The trend of surface ozone in Taipei, Taiwan, and its causes: Implications for ozone control strategies, Atmos. Environ., 40, 3898–3908, 2006. Chou, M. D. and Suarez, M. J.: An efficient thermal infrared radiation parameterization for use in general circulation models, NASA Tech. Memo. 104606, 3, 85 pp., 1994. Colman, J. J., Swanson, A., Meinardi, S., Sive, B. C., Blake, D. R., and Rowland, F. S.: Description of the analysis of a wide range of volatile organic compounds in whole air samples collected during PEM-Tropics A and B, J. Anal. Chem., 73, 3723–3731, 2001. Crowley, J. N., Schuster, G., Pouvesle, N., Parchatka, U., Fischer, H., Bonn, B., Bingemer, H., and Lelieveld, J.: Nocturnal nitrogen oxides at a rural mountain-site in south-western Germany, Atmos. Chem. Phys., 10, 2795–2812, <a href="http://dx.doi.org/10.5194/acp-10-2795-2010">https://doi.org/10.5194/acp-10-2795-2010</a>, 2010. Ding, A. J., Wang, T., Zhao M., Wang, T. J., and Li, Z. K.: Simulation of sea-land breezes and a discussion of their implications on the transport of air pollution during a multi-day ozone episode in the Pearl River Delta of China, Atmos. Environ., 38, 6737–6750, 2004. Ding, A. J., Wang, T., Thouret, V., Cammas, J.-P., and Nédélec, P.: Tropospheric ozone climatology over Beijing: analysis of aircraft data from the MOZAIC program, Atmos. Chem. Phys., 8, 1–13, <a href="http://dx.doi.org/10.5194/acp-8-1-2008">https://doi.org/10.5194/acp-8-1-2008</a>, 2008. Dodge, M. C.: Combined use of modeling techniques and smog chamber data to derive ozone-precursor relationships. International Conference on Photochemical Oxidant Pollution and its Control: Proceedings, Vol. II B, EPA/600/3-77-001b, US Environmental Protection Agency, Research Triange Park, NC, 881–889, 1977. Done, J., Davis, C., and Weisman, M.: The next generation of NWP: Explicit forecasts of convection using the Weather Research and Forecast (WRF) model, Atmos. Sci. Lett., 5, 110–117, <a href="http://dx.doi.org/10.1002/asl.72">https://doi.org/10.1002/asl.72</a>, 2004. Doran, J. C., Berkowitz, C. M., Coulter, R. L., Spicer, C. W., and Shaw, W. J.: The 2001 Phoenix Sunrise experiment: vertical mixing and chemistry during the morning transition in Phoenix, Atmos. Environ., 37, 2365–2377, 2003. Ehhalt, D. H., Rohrer, F., Wahner, A., Prather, M. J., and Blake, D. R.: On the use of hydrocarbons for the determination of tropospheric OH concentrations, J. Geophys. Res., 103, 18981–18997, 1998. Evtyugina, M. G., Nunes, T., Alves, C., and Marques, M. C.: Photochemical pollution in a rural mountainous area in the northeast of Portugal, Atmos. Res., 92, 151–158, 2009. Finlayson-Pitts, B. J. and Pitts, N.: VOCs, NO<i><sub>x</sub></i> and ozone production, J. Air Waste Manage., 43, 1093–1101, 1993. Fu, P. Q., Kawamura, K., Kanaya, Y., and Wang, Z. F.: Contributions of biogenic volatile organic compounds to the formation of secondary organic aerosols over Mt. Tai, Central East China, Atmos. Environ., 44, 4817–4826, 2010. Gao, J., Wang, T., Ding, A. J., and Liu, C. B.: Observational study of ozone and carbon monoxide at the summit of mount Tai (1534 m a.s.l.) in central-eastern China, Atmos. Environ., 39, 4779–4791, 2005. Grell, G. A. and Dévényi, D.: A generalized approach to parameterizing convection combining ensemble and data assimilation techniques, Geophys. Res. Lett., 29, 1693, <a href="http://dx.doi.org/10.1029/2002GL015311">https://doi.org/10.1029/2002GL015311</a>, 2002. Guo, H., Jiang, F., Cheng, H. R., Simpson, I. J., Wang, X. M., Ding, A. J., Wang, T. J., Saunders, S. M., Wang, T., Lam, S. H. M., Blake, D. R., Zhang, Y. L., and Xie, M.: Concurrent observations of air pollutants at two sites in the Pearl River Delta and the implication of regional transport, Atmos. Chem. Phys., 9, 7343–7360, <a href="http://dx.doi.org/10.5194/acp-9-7343-2009">https://doi.org/10.5194/acp-9-7343-2009</a>, 2009. Guo, H., Ling, Z. H., Simpson, I. J., Blake, D. R., and Wang, D. W.: Observations of isoprene, methacrolein (MAC) and methyl vinyl ketone (MVK) at a mountain site in Hong Kong, J. Geophys. Res., 117, D19303, <a href="http://dx.doi.org/10.1029/2012JD017750">https://doi.org/10.1029/2012JD017750</a>, 2012. Ho, K. F., Lee, S. C., Ho, W. K., Blake, D. R., Cheng, Y., Li, Y. S., Ho, S. S. H., Fung, K., Louie, P. K. K., and Park, D.: Vehicular emission of volatile organic compounds (VOCs) from a tunnel study in Hong Kong, Atmos. Chem. Phys., 9, 7491–7504, <a href="http://dx.doi.org/10.5194/acp-9-7491-2009">https://doi.org/10.5194/acp-9-7491-2009</a>, 2009. Ho, K. F., Lee, S. C., Guo, H., Tsai, W. Y.: Seasonal and diurnal variations of volatile organic compounds (VOCs) in the atmosphere of Hong Kong, Sci. Total Environ., 322, 155–166, 2004. Hong Kong Environmental Protection Department (HKEPD): An overview on air quality and air pollution control in Hong Kong, <a href="http://www.epd.gov.hk/epd/english/environmentinhk/air/air_maincontent.html">http://www.epd.gov.hk/epd/english/environmentinhk/air/air_maincontent.html</a>, 2010. Hong Kong Environmental Protection Department (HKEPD): Air Quality in Hong Kong 2011 (Preliminary Report), Air Science Group, Environmental Protection Department, the Government of the Hong Kong Special Administrative Region, 2012. Hong, S. Y., Dudhia, J., and Chen, S.-H.: A revised approach to ice-microphysical processes for the bulk parameterization of cloud and precipitation, Mon. Weather Rev., 132, 103–120, 2004. Hong, S. Y., Noh, Y., and Dudhia, J.: A new vertical diffusion package with explicit treatment of entrainment processes, Mon. Weather Rev., 134, 2318–2341, 2006. Huang, J. P., Fung, J. C. H., and Lau, A. K. H.: Integrated processes analysis and systematic meteorological classification of ozone episodes in Hong Kong, J. Geophys. Res., 111, D20309, https://doi.org/10/1029/2005JD007012, 2006. IPCC (Intergovernmental Panel on Climate Change): The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge Univ. Press, Cambridge, UK, 2007. Jenkin, M. E. and Clemitshaw, K. C.: Ozone and other secondary photochemical pollutants: chemical processes governing their formation in the planetary boundary layer, Atmos. Environ., 34, 2499–2527, 2000. Jenkin, M. E., Saunders, S. M., Wagner, V., and Pilling, M. J.: The tropospheric degradation of volatile organic compounds: A protocol for mechanism development, Atmos. Environ., 31, 81–107, 1997. Jenkin, M. E., Saunders, S. M., Wagner, V., and Pilling, M. J.: Protocol for the development of the Master Chemical Mechanism, MCM v3 (Part B): tropospheric degradation of aromatic volatile organic compounds, Atmos. Chem. Phys., 3, 181–193, <a href="http://dx.doi.org/10.5194/acp-3-181-2003">https://doi.org/10.5194/acp-3-181-2003</a>, 2003. Jiang, F., Wang, T. J., Wang, T. T., Xie, M., and Zhao, H.: Numerical modeling of a continuous photochemical pollution episode in Hong Kong using WRF-chem., Atmos. Environ., 42, 8717–8727, 2008. Jiang, F., Guo, H., Wang, T. J., Cheng, H. R., Wang, X. M., Simpson, I. J., Ding, A. J., Saunders, S. M., Lam, S. H. M., and Blake, D. R.: An ozone episode in the Pearl River Delta: Field observation and model simulation, J. Geophys. Res., 115, D22305, <a href="http://dx.doi.org/10.1029/2009JD013583">https://doi.org/10.1029/2009JD013583</a>, 2010. Jobson, B. T., Mckeen, S. A., and Parrish, D. D.: Spatial and temporal variability of nonmethane hydrocarbon mixing ratios and their relation to photochemical lifetime, J. Geophys. Res., 103, 13557–13567, 1998. Lam, S. H. M., Ling, Z. H., Guo, H., Saunders, S. M., Jiang, F., Wang, X. M., and Wang, T. J.: Modelling VOC source impacts on high ozone episode days observed at a mountain summit in Hong Kong under the influence of mountain-valley breezes, J. Environ. Manage., submitted, 2013. Li, J., Pochanart, P., Wang, Z. F., Liu, Y., Yamaji, K., Takigawa, M., Kanaya, Y., and Akimoto, H.: Impact of chemical production and transport on summertime diurnal ozone behavior at a mountainous site in North China Plain, Sola, 4, 121–124, 2008. Lin, C. H., Lai, C. H., Wu, Y. L., Lai, H. C., and Lin, P. H.: Vertical ozone distributions observed using tethered ozonesondes in a coastal industrial city, Kaohsiung, in southern Taiwan, Environ. Monit. Assess., 127, 253–270, 2007. Ling, Z. H., Guo, H., Cheng, H. R., and Yu, Y. F.: Sources of ambient volatile organic compounds and their contributions to photochemical ozone formation at a site in the Pearl River Delta, southern China, Environ. Pollut., 159, 2310–2319, 2011. Liu, H. P., Chan, J. C. L., and Cheng, A. Y. S.: Internal boundary layer structure under sea-breeze conditions in Hong Kong, Atmos. Environ., 35, 683–692, 2000. Liu, Y., Shao, M., Kuster, W. C., Goldan, P. D., Li, X. H., Lu, S. H., and de Gouw, J. A.: Source identification of reactive hydrocarbons and oxygenated VOCs in the summertime in Beijing, Environ. Sci. Technol., 43, 75–81, 2009. Ma, Z. Q., Zhang, X. L., Xu, J., Zhao, X. J., and Wei, M.: Characteristics of ozone vertical profile observed in the boundary layer around Beijing in autumn, J. Environ. Sci., 23, 1316–1324, 2011. Mlawer, E. J., Taubman, S. J., Brown, P. D., Iacono, M. J., and Clough, S. A.: Radiative transfer for inhomogeneous atmospheres: RRTM, a validated correlated-k model for the longwave, J. Geophys. Res., 102D, 16663–16682, 1997. Monteiro, A., Strunk, A., Carvalho, A., Tchepep, O., Miranda, A. I., Borrego, C., Saavedra, S., Rpdríguez, A., Souto, J., Casares, J., Friese, E., and Elbern, H.: Investigating a high ozone episode in a rural mountain site, Environ. Pollut., 162, 176–189, 2012. NESCAUM (Northeast States for Coordinated Air Use Management), 1995: Preview of 1994. NRC (National Research Council): The effects of meteorological on tropospheric ozone, in: Rethinking the ozone problem in urban and regional air pollution, National Academy Press, Washington, DC, USA, 1991. Ou Yang, C. F., Liu, N. H., Sheu, G. R., Lee, C. T., and Wang, J. L.: Seasonal and diurnal variations of ozone at a high-altitude mountain baseline station in East Asia, Atmos. Environ., 46, 279–288, 2012. Parrish, D. D., Buhr, M. P., Trainer, M., Northon, R. B., Shimshock, J. P., Fehsenfeld, F. C., Anlauf, K. G., Bottenheim, J. W., Tang, Y. Z., Wiebe, H. A., Roberts, J. M., Tanner, R. L., Newman, L., Bowersox, V. C., Olszyna, K. J., Bailey, E. M., Rodgers, M. O., Wang, T., Berresheim, H., Roychowdhury, U. K., and Demerjiani, K. L.: The total reactive oxidized nitrogen levels and their partitioning between the individual species at six rural sites in eastern North America, J. Geophys. Res., 98, 2927–2939, 1993. Pochanart, P., Akimoto, H., Kajii, Y., Potemkin, V. M., and Khodzher, V. T.: Regional background ozone and carbon monoxide variations in remote Siberia/east Asia, J. Geophys. Res., 108, 4028, <a href="http://dx.doi.org/10.1029/2001JD001412">https://doi.org/10.1029/2001JD001412</a>, 2003. PORG (Photochemical Oxidants Review Group): Ozone in the United Kingdom, Fourth Report of the UK photochemical Oxidants review group, Department of the Environment, Transport and the Regions, London, 1997. Reeves, C. E., Slemr, J., Oram, D. E., Worton, D., Penkett, S. A., Stewart, D. J., Purvis, R., Watson, N., Hopkins, J., Lewis, A., Methven, J., Blake, D. R., and Atlas, E.: Alkyl nitrates in outflow from North America over the North Atlantic during Intercontinental Transport of Ozone and Precursors 2004, J. Geophys. Res., 112, D10S37, <a href="http://dx.doi.org/10.1029/2006JD007567">https://doi.org/10.1029/2006JD007567</a>, 2007. Roberts, J. M., Bertman, S. B., Parrish, D. D., Fehsenfeld, F. C., Jobson, B. T., and Niki, H.: Measurement of alkyl nitrates at Chebogue Point, Nova Scotia during the 1993 North Atlantic Regional Experiment (NARE) intensive, J. Geophys. Res., 103, 13569–13580, 1998. Saunders, S. M., Jenkin, M. E., Derwent, R. G., and Pilling, M. J.: Protocol for the development of the Master Chemical Mechanism, MCM v3 (Part A): tropospheric degradation of non-aromatic volatile organic compounds, Atmos. Chem. Phys., 3, 161–180, <a href="http://dx.doi.org/10.5194/acp-3-161-2003">https://doi.org/10.5194/acp-3-161-2003</a>, 2003. Scott, B. and Ahmet, P.: Influence of synoptic and mesoscale meteorology on ozone pollution potential for San Joaquin Valley of California, Atmos. Environ., 43, 1779–1788, 2009. Sillman, S.: The relation between ozone, NO<i><sub>x</sub></i> and hydrocarbons in urban and polluted rural environments, Atmos. Environ., 33, 1821–1845, 1999. Sillman, S., He, D. Y., and Pippin, M. R.: Model correlations for ozone, reactive nitrogen, and peroxides for Nashville in comparison with measurements: Implications for O<sub>3</sub>-NO<i><sub>x</sub></i>-hydrocarbon chemistry, J. Geophys. Res., 103, 22629–22644, 1998. Sillman, S., Vautard, R., Menut, L., and Kley, D.: O<sub>3</sub>-NO<i><sub>x</sub></i>-VOC sensitivity and NO<i><sub>x</sub></i>-VOC indicators in Paris: Results from models and atmospheric pollution over the Paris Area (ESQUIF) measurements, J. Geophys. Res., 108, 8563, <a href="http://dx.doi.org/10.1029/2002JD001561">https://doi.org/10.1029/2002JD001561</a>, 2003. Simpson, I. J., Blake, N. J., Barletta, B., Diskin, G. S., Fuelberg, H. E., Gorham, K., Huey, L. G., Meinardi, S., Rowland, F. S., Vay, S. A., Weinheimer, A. J., Yang, M., and Blake, D. R.: Characterization of trace gases measured over Alberta oil sands mining operations: 76 speciated C<sub>2</sub>–C<sub>10</sub> volatile organic compounds (VOCs), CO<sub>2</sub>, CH<sub>4</sub>, CO, NO, NO<sub>2</sub>, NO<sub>y</sub>, O<sub>3</sub> and SO<sub>2</sub>, Atmos. Chem. Phys., 10, 11931–11954, <a href="http://dx.doi.org/10.5194/acp-10-11931-2010">https://doi.org/10.5194/acp-10-11931-2010</a>, 2010. Skamarock, W. C. and Klemp, J. B.: A time split non hydrostatic atmospheric model for weather research and forecasting applications, J. Comput. Phys., 227, 7, 3465–3485, 2008. So, K. L. and Wang, T.: On the local and regional influence on ground-level ozone concentrations in Hong Kong, Environ. Pollut., 123, 307–317, 2003. Steinbacher, M., Zellweger, C., Schwarzenbach, B., Bugmann, S., Buchmann, B., Ordónez, C., Prevot, A., and Hueglin, C.: Nitrogen oxide measurements at rural sites in Switzerland: Bias of conventional measurement techniques, J. Geophys. Res., 112, D11307, <a href="http://dx.doi.org/10.1029/2001JD001412">https://doi.org/10.1029/2001JD001412</a>, 2007. Steven, E. K., Benjamin, S. G., McGinley, J. A., Brown, J. M., Schultz, P., Szoke, E. J., Smirnova, T. G., Shaw, B. L., Birkenheuer, D., Albers, S., Peckham, S., and Grell, G.: Real-time Applications of the WRF Model at the Forecast Systems Laboratory, 84th AMS Annual Meeting, Seattle, USA, 10–15 January 2004. Tang, G., Wang, Y., Li, X., Ji, D., Hsu, S., and Gao, X.: Spatial-temporal variations in surface ozone in Northern China as observed during 2009–2010 and possible implications for future air quality control strategies, Atmos. Chem. Phys., 12, 2757–2776, <a href="http://dx.doi.org/10.5194/acp-12-2757-2012">https://doi.org/10.5194/acp-12-2757-2012</a>, 2012. Tang, J. H., Chan, L. Y., Chan, C. Y., Li, Y. S., Chang, C. C., Wang, X. M., Zou, S. C., Barletta, B., Blake, D. R., and Wu, D.: Implications of changing urban and rural emissions on non-methane hydrocarbons in the Pearl River Delta region of China, Atmos. Environ., 42, 3780–3794, 2008. Tseng, K. H., Chen, C. L., Lin, M. D., Chang, K. H., and Tsuang, B. J.: Vertical profile of ozone and accompanying air pollutant concentrations observed at a downwind foothill site of industrial and urban areas, Aerosol Air Qual. Res., 9, 421–434, 2009. Tsai, W. Y., Chan, L. Y., Blake, D. R., and Chu, K. W.: Vehicular fuel composition and atmospheric emissions in South China: Hong Kong, Macau, Guangzhou, and Zhuhai, Atmos. Chem. Phys., 6, 3281–3288, <a href="http://dx.doi.org/10.5194/acp-6-3281-2006">https://doi.org/10.5194/acp-6-3281-2006</a>, 2006. Turnipseed, A. A., Anderson, D. E., Burns, S., Blanken, P. D., and Monson, R. K.: Airflows and turbulent flux measurements in mountainous terrain Part 2: mesoscale effects, Agr. Forest Meterol., 125, 187–205, 2004. Wang, T. and Kwok, J. Y. H.: Measurement and analysis of a multi-day photochemical smog episode in the Pearl River Delta of China, J. Appl. Meteorol., 42, 404-416, 2003. Wang, T., Cheung, V. T. F., Lam, K. S., Kok, G. L., and Harris, J. M.: The characteristics of ozone and related compounds in the boundary layer of the South China coast: temporal and vertical variations during autumn season, Atmos. Environ., 35, 2735–2746, 2001. Wang, T., Poon, C. N., Kwok, Y. H., and Li, Y. S.: Characterizing the temporal variability and emission patterns of pollution plumes in the Pearl River Delta of China, Atmos. Environ., 37, 3539–3550, 2003. Wang, T., Guo, H., Blake, D. R., Kwok, Y. H., Simpson, I. J., and Li, Y. S.: Measurements of trace gases in the inflow of South China Sea background air and outflow of regional pollution at Tai O, Southern China, J. Atmos. Chem., 52, 295–317, 2005. Wang, T., Wong, H. L. A., Tang, J., Ding, A., Wu, W. S., and Zhang, X. C.: On the origin of surface ozone and reactive nitrogen observed at remote site in the northeastern Qinghai-Tibetan Plateau, western China, J. Geophys. Res., 111, D08303, <a href="http://dx.doi.org/10.1029/2005JD006527">https://doi.org/10.1029/2005JD006527</a>, 2006. Wang, T., Wei, X. L., Ding, A. J., Poon, C. N., Lam, K. S., Li, Y. S., Chan, L. Y., and Anson, M.: Increasing surface ozone concentrations in the background atmosphere of Southern China, 1994–2007, Atmos. Chem. Phys., 9, 6217–6227, <a href="http://dx.doi.org/10.5194/acp-9-6217-2009">https://doi.org/10.5194/acp-9-6217-2009</a>, 2009. Warneke, C. and de Gouw, J. A.: Organic trace gas composition of the marine boundary layer over the northwest India Ocean in April 2000, Atmos. Environ., 35, 5923–5933, 2001. Xu, Z., Wang, T., Xue, L. K., Louie, P., Luk, C., Gao, J., Wang, S. L., Chai, F. H., an Wang, W. X.: Evaluating the uncertainties of thermal catalytic conversion for measuring atmospheric nitrogen dioxide at four polluted sites in China, Atmos. Environ., <a href="http://dx.doi.org/10.1016/j.atmosenv.2012.09.043">https://doi.org/10.1016/j.atmosenv.2012.09.043</a>, in press, 2013. Xue, L. K., Wang, T., Zhang, J. M., Zhang, X. C., Delig-Geer, Poon, C. N., Ding, A. J., Zhou, X. H., Wu, W. S., Tang, J., Zhang, Q. Z., and Wang, W. X.: Source of surface ozone and reactive nitrogen speciation at Mount Waliguan in Western China: New insights from the 2006 summer study, J. Geophys. Res., 116, D07306, <a href="http://dx.doi.org/10.1029/2010JD014735">https://doi.org/10.1029/2010JD014735</a>, 2011. Yuan, B., Shao, M., de Gouw, J., Parrish, D. D., Lu, S. H., Wang, M., Zeng, L. M., Zhang, Q., Song, Y., Zhang, J. B., and Hu, M.: Volatile Organic Compounds (VOCs) in Urban Air: How Chemistry Affects the Interpretation of Positive Matrix Factorization (PMF) Analysis, J. Geophys. Res., 117, D24, <a href="http://dx.doi.org/10.1029/2012JD018236">https://doi.org/10.1029/2012JD018236</a>, 2012. Zanis, P., Ganser, A., Zellweger, C., Henne, S., Steinbacher, M., and Staehelin, J.: Seasonal variability of measured ozone production efficiencies in the lower free troposphere of Central Europe, Atmos. Chem. Phys., 7, 223–236, <a href="http://dx.doi.org/10.5194/acp-7-223-2007">https://doi.org/10.5194/acp-7-223-2007</a>, 2007. Zellweger, C., Forrer, J., Hofer, P., Nyeki, S., Schwarzenbach, B., Weingartner, E., Ammann, M., and Baltensperger, U.: Partitioning of reactive nitrogen (NOy) and dependence on meteorological conditions in the lower free troposphere, Atmos. Chem. Phys., 3, 779–796, <a href="http://dx.doi.org/10.5194/acp-3-779-2003">https://doi.org/10.5194/acp-3-779-2003</a>, 2003. Zhang, D. and Anthes, R. A.: A high-resolution model of the planetary boundary layer – sensitivity tests and comparison with SESAME-79 data, J. Appl. Meteorol., 21, 1594–1609, 1982. Zhang, J., Wang, T., Chameides, W. L., Cardelino, C., Kwok, J., Blake, D. R., Ding, A., and So, K. L.: Ozone production and hydrocarbon reactivity in Hong Kong, Southern China, Atmos. Chem. Phys., 7, 557–573, <a href="http://dx.doi.org/10.5194/acp-7-557-2007">https://doi.org/10.5194/acp-7-557-2007</a>, 2007. Zhang, L. F. and Zhang, M.: Study of the sea-land breeze system in Hong Kong, HKMetS Bulletin, 7, 22–42, 1997. Zhang, Y. H., Su, H., Zhong, L. J., Cheng, Y. F., Zeng, L. M., Wang, X. S., Xiang, Y. R., Wang, J. L., Gao, D. F., Shao, M., Fan, S. J., and Liu, S. C.: Regional ozone pollution and observation-based approach for analyzing ozone-precursor relationship during the PRIDE-PRD2004 campaign, Atmos. Environ., 42, 6203–6218, 2008. Zhang, Y. L., Wang, X. M., Blake, D. R., Li, L. F., Zhang, Z., Wang, Shao, Y., Guo, H., Lee, S. C., Guo, B., Chan, L. Y., Wu, D., and Rowland, F. S.: Aromatic hydrocarbons as ozone precursors before and after outbreak of the 2008 financial crisis in the Pearl River Delta region, south China, J. Geophys. Res.-Atmos., 117, D15306, <a href="http://dx.doi.org/10.1029/2011JD017356">https://doi.org/10.1029/2011JD017356</a>, 2012. Zhao, Y., Shao, M., Wang, C., Wang, B. G., Lu, S. H., and Zhong, L. J.: Characterizing spatial patterns of NO<i><sub>x</sub></i>, SO<sub>2</sub> and O<sub>3</sub> in Pearl River Delta by Passive Sampling, J. Environ. Sci., 32, 324–329, 2011.