Photochemical smog, characterized by high concentrations of ozone (O) and fine particles (PM) in the atmosphere, has become one of the top environmental concerns in China. Volatile organic compounds (VOCs), one of the key precursors of O and secondary organic aerosol (SOA) (an important component of PM), have a critical influence on atmospheric chemistry and subsequently affect regional and global climate. Thus, VOCs have been extensively studied in many cities and regions in China, especially in the North China Plain, the Yangtze River Delta and the Pearl River Delta regions where photochemical smog pollution has become increasingly worse over recent decades. This paper reviews the main studies conducted in China on the characteristics and sources of VOCs, their relationship with O and SOA, and their removal technology. This paper also provides an integrated literature review on the formulation and implementation of effective control strategies of VOCs and photochemical smog, as well as suggestions for future directions of VOCs study in China.
Ozone (O3), a main component in photochemical smog, is a secondary pollutant formed through complex photochemical reactions involving nitrogen oxides (NOx) and volatile organic compounds (VOCs).
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.
Abstract. In the summer of 2017, measurements of ozone (O3) and its precursors were
carried out at an urban site in Jinan, a central city in the North China
Plain (NCP). A continuous O3 pollution event was captured during
4–11 August, with the maximum hourly O3 mixing ratio reaching 154.1 ppbv.
Model simulation indicated that local photochemical formation and regional
transport contributed 14.0±2.3 and 18.7±4.0 ppbv h−1, respectively, to the
increase in O3 during 09:00–15:00 LT (local time) in this event.
For local O3 formation, the calculated OH
reactivities of volatile organic compounds (VOCs) and carbon monoxide (CO)
were comparable between O3 episodes and non-episodes (p>0.05), so
was the OH reactivity of nitrogen oxides (NOx). However, the
ratio of OH reactivity of VOCs and CO to that of NOx
increased from 2.0±0.4 s−1 s1 during non-episodes to
3.7±0.7 s−1 s1 during O3 episodes, which resulted in the change in
the O3 formation mechanism from the VOC-limited regime before the
O3 pollution event to the transitional regime during the event.
Correspondingly, the simulated local O3 production rate during the
event (maximum: 21.3 ppbv h−1) was markedly higher than that before
the event (p<0.05) (maximum: 16.9 ppbv h−1). Given that gasoline and
diesel exhaust made large contributions to the abundance of O3
precursors and the O3 production rate, constraint on vehicular
emissions is the most effective strategy to control O3 pollution in
Jinan. The NCP has been confirmed as a source region of tropospheric
O3, where the shift in regimes controlling O3 formation
like the case presented in this study can be expected across the entire
region, due to the substantial reductions of NOx emissions
in recent years.
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