Abstract
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.
Highlights
Air pollution in the North China Plain (NCP), the largest alluvial plain of China consisting of Beijing, Tianjin and many cities in Hebei, Shandong and Henan provinces, has attracted much attention in recent years
In view of the comparable O3 mixing ratios observed at our sampling site to those at the surrounding air quality monitoring stations (AQMSs), we believe that the observations at our sampling site to some extent represented the characteristics of this regional pollution event
The OH reactivity of Volatile organic compounds (VOCs) was categorized into carbonyls, biogenic VOCs (BVOCs), aromatics, alkenes and alkanes (Table S3 lists the VOCs included in each group)
Summary
Air pollution in the North China Plain (NCP), the largest alluvial plain of China consisting of Beijing, Tianjin and many cities in Hebei, Shandong and Henan provinces, has attracted much attention in recent years. X. Lyu et al.: Causes of a continuous summertime O3 pollution event in Jinan the NCP in a mountainous area to the north of Beijing, Wang et al (2006) reported the maximum hourly O3 mixing ratio of 286 ppbv. The strong photochemical production of O3 in urban plumes of Beijing was found by Wang et al (2006), while the contribution of regional transport was revealed by the enhanced O3 production at a rural site in the NCP under southerly winds (Lin et al, 2008). Almost no study was carried out to explore the mechanisms responsible for high O3 there, though it has been confirmed that air pollution in the cities like Jinan in the NCP influenced air quality in Beijing (Lin et al, 2008; Wang et al, 2010). We proposed feasible O3 control measures based on the source-resolved OH reactivity of VOCs and NOx
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