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.</p
