Abstract：
Continuous measurements of ozone (O3) and nitrogen oxides (NOx = NO + NO2) were conducted from 2007 to 2019 in Hong Kong in order to evaluate the effectiveness of control strategies for NOx emission from diesel commercial vehicles (DCV). DCV control programs were periodically applied in three phases starting from 2007, 2010 and 2014. It was found that NO and NO2 levels decreased during the study period but more dramatically after the implementation of DCV Phase III than pre-DCV Phase III. Source apportionment analysis confirmed that the ambient NO and NO2 in Hong Kong attributed to the regulated DCV emissions in Phase III reduced at rates of 5.1-14.4 ppbv/yr in roadside environment and 1.6-3.1 ppbv/yr in suburban area. Despite overall NOx reduction, increased NO2/NOx ratios were recorded during the study period possibly due to the application of diesel particulate filter (DPF) in DCVs. However, after introducing DCV Phase III, observed O3 values experienced more dramatic increasing trends in most areas of Hong Kong than pre-DCV Phase III. Model simulations revealed that O3 production rate kept increasing and turned to be less sensitive to NOx from 2014 to 2019. On the roadside, net O3 production rate was more than doubled during 2014-2019 owing to NOx reduction. Moreover, the levels of oxidants (OH, HO2 and RO2) were 1.5-5 times those before 2014. In suburban environment, NOx reduction also facilitated O3 production and radical cycling, but made smaller contributions than those on the roadside during 2014-2019. This study unraveled that NOx reductions benefited from DCV regulations caused increase in surface O3 and fueled O3 photochemistry in various environments. More stringent control measures on emissions of VOCs, especially those with high OH reactivity, might help to better mitigate O3 pollution.
摘要：
2007年至2019年在香港进行了臭氧（O3）和氮氧化物（NOx=NONO2）的连续测量，以评估柴油商用车（DCV）NOx排放控制策略的有效性。从2007年，2010年和2014年开始，DCV控制程序分三个阶段定期应用。发现NO和NO2水平在研究期间降低,但在实施DCV阶段III之后比DCV阶段III之前更显著。来源分配分析证实，由于第三阶段受管制的DCV排放，香港的环境NO和NO2在路边环境中以5.1-14.4ppbv/yr的速率减少，在郊区以1.6-3.1ppbv/yr的速率减少。尽管总体上减少了NOx，在研究期间记录了增加的NO2/NOx比率，这可能是由于在DCV中应用了柴油颗粒过滤器（DPF）。然而,在引入DCV第三阶段之后，与DCV第三阶段之前相比，香港大部分地区的观察到的O3值经历了更急剧的增长趋势。模型模拟显示，从2014年到2019年，O3的生产率一直在增加，并且对NOx的敏感性降低。在路边,由于减少了NOx，2014-2019年的净O3生产率增加了一倍以上。此外，氧化剂的水平(OH，HO2和RO2）是2014年之前的1.5-5倍。在郊区环境中，NOx还原还促进了O3的产生和自由基循环，但在2014-2019年期间做出的贡献少于路边的贡献。这项研究揭示了从DCV法规中受益的NOx还原导致各种环境中表面O3和燃料O3光化学的增加。更加严格的挥发性有机化合物排放控制措施，尤其是那些具有高OH反应性的，可能有助于更好地减轻O3污染。
