Ground-level ozone in four Chinese cities: precursors, regional transport and heterogeneous processes

Abstract

Abstract. We analyzed the measurements of ozone (O3) and its precursors made at rural/suburban sites downwind of four large Chinese cities – Beijing, Shanghai, Guangzhou and Lanzhou, to elucidate their pollution characteristics, regional transport, in situ production, and impacts of heterogeneous processes. The same measurement techniques and observation-based model were used to minimize uncertainties in comparison of the results due to difference in methodologies. All four cities suffered from serious O3 pollution but showed different precursor distributions. The model-calculated in situ O3 production rates were compared with the observed change rates to infer the relative contributions of on-site photochemistry and transport. At the rural site downwind of Beijing, export of the well-processed urban plumes contributed to the extremely high O3 levels (up to an hourly value of 286 ppbv), while the O3 pollution observed at suburban sites of Shanghai, Guangzhou and Lanzhou was dominated by intense in situ production. The O3 production was in a volatile organic compound (VOC)-limited regime in both Shanghai and Guangzhou, and a NOx-limited regime in Lanzhou. The key VOC precursors are aromatics and alkenes in Shanghai, and aromatics in Guangzhou. The potential impacts on O3 production of several heterogeneous processes, namely, hydrolysis of dinitrogen pentoxide (N2O5), uptake of hydro peroxy radical (HO2) on particles and surface reactions of NO2 forming nitrous acid (HONO), were assessed. The analyses indicate the varying and considerable impacts of these processes in different areas of China depending on the atmospheric abundances of aerosol and NOx, and suggest the urgent need to better understand these processes and represent them in photochemical models.

Role of ambient ammonia in particulate ammonium formation at a rural site in the North China Plain

“…Xue et al, 2014). The NO x concentration during night-time was higher than during daytime, while the NO ing night-time was only slightly higher than that during daytime.…”

Production of N<sub>2</sub>O<sub>5</sub> and ClNO<sub>2</sub> in summer in urban Beijing, China

“…All these results highlight the fact that N 2 O 5 heterogeneous uptake might be an important pathway of nitrate formation in Beijing. A recent modeling study has evaluated the impacts of heterogeneous ClNO 2 formation on next-day ozone formation in Beijing (Xue et al, 2014b). However, the roles of N 2 O 5 in nitrate formation and of N 2 O 5 and ClNO 2 in nighttime and daytime chemistry in summer in urban Beijing during field campaigns are not characterized yet, except for one measurement in suburban Beijing in the summer of 2016 .…”

Hotspot of glyoxal over the Pearl River delta seen from the OMI satellite instrument: implications for emissions of aromatic hydrocarbons

“…Surface O 3 and PM are routinely in excess of Chinese national ambient air quality standards (Liu et al, 2013). Ozone production in the PRD is predominantly VOC-limited (Zhang et al, 2007Wang et al, 2010; Shao et al, 2009;Xue et al, 2014), and the aromatic species toluene and xylene play a dominant role (Xue et al, 2014). Aromatics have also been identified as an important regional source of secondary organic aerosol via reactive uptake of their oxidation products (Li et al, 2013), including glyoxal (Fu et al, 2008).…”