Long-term O<sub>3</sub>–precursor relationships in Hong Kong: field observation and model simulation

Abstract

Abstract. Over the past 10 years (2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014), ground-level O 3 in Hong Kong has consistently increased in all seasons except winter, despite the yearly reduction of its precursors, i.e. nitrogen oxides (NO x = NO + NO 2 ), 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 O 3 and regional transport. The simulation of locally produced O 3 showed an increasing trend in spring, a decreasing trend in autumn, and no changes in summer and winter. The O 3 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 O 3 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 O 3 formation in autumn was overridden by the regional contribution, resulting in elevated O 3 observations. Furthermore, the OBM-derived relative incremental reactivity indicated that the O 3 formation was VOClimited in all seasons, and that the long-term O 3 formation was more sensitive to VOCs and less to NO x and CO in the past 10 years. In addition, the OBM results found that the contributions of aromatics to O 3 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.

Ozone pollution around a coastal region of South China Sea: interaction between marine and continental air

“…Figure 3 illustrates surface wind fields and air movement 2 days (i.e., 20-21 September) before the occurrence of Usagi as an example. It can be seen that when Usagi approached southeastern area of Hong Kong, it led to weak northeasterly and later northwesterly winds which potentially delivered O 3 and its precursors from highly polluted inland PRD region to the sampling sites (Yin, 2004;Wei et al, 2016;Wang et al, 2017). The wind speed was lower than 4 m s −1 at the sampling sites and in their surrounding area on 20 September (Fig.…”

“…However, increasing studies showed that surface O 3 was elevated rapidly in East Asia in the last decade (Ding et al, 2008;Xu et al, 2008;Parrish et al, 2012;Xue et al, 2014;Zhang et al, 2014;Sun et al, 2016;Lin et al, 2017;Wang et al, 2017). For example, the observational data revealed that regional O 3 concentrations increased at a rate of 0.86 ppbv yr −1 in Pearl River Delta (PRD) from 2006 to 2011 (Li et al, 2014), at a rate of 0.56 ppbv yr −1 in Hong Kong from 2005 to 2014 (Wang et al, 2017), and even at a rate of 1.7-2.1 ppbv yr −1 (summertime only) at Mount Tai in central eastern China (Sun et al, 2016).…”

“…Since the sampling interval was 2 h for each sample, cubic spline interpolation was used to derive VOC concentrations at each hour for modeling purpose. Please see our previous publication for details (Wang et al, 2017). HONO has been recognized as an important source of OH, influencing O 3 formation significantly (Kleffmann, 2007).…”

“…The arrival of oceanic air masses generally brings substantial marine-originated compounds (e.g., dimethyl sulfide) to the continent and significantly alleviates the anthropogenic air pollution there. In fact, this is one of the main reasons for low-O 3 mixing ratio observed in the PRD region in summertime when southwestern winds prevail (T. Wang et al, 2009;Y. Wang et al, 2017).…”

Long-term measurements of ground-level ozone in Windsor, Canada – Part I. temporal variations and trends

“…Similarly, a study in Hong Kong investigated associations between O 3 and its precursors, i.e. NO X and 21 NMHCs during 2005-2014 (Wang et al, 2017). O 3 concentrations in Hong Kong increased (0.56 ppb/year, p<0.01) while NOx decreased (-0.71 ppb/year, p<0.01).…”