Abstract
Abstract. The characteristics of ozone variations and the impacts of synoptic and local meteorological factors in northern China were quantitatively analyzed during the warm season from 2013 to 2017 based on multi-city in situ ozone and meteorological data as well as meteorological reanalysis. The domain-averaged maximum daily 8 h running average O3 (MDA8 O3) concentration was 122±11 µg m−3, with an increase rate of 7.88 µg m−3 yr−1, and the three most polluted months were closely related to the variations in the synoptic circulation patterns, which occurred in June (149 µg m−3), May (138 µg m−3) and July (132 µg m−3). A total of 26 weather types (merged into five weather categories) were objectively identified using the Lamb–Jenkinson method. The highly polluted weather categories included the S–W–N directions (geostrophic wind direction diverts from south to north), low-pressure-related weather types (LP) and cyclone type, which the study area controlled by a low-pressure center (C), and the corresponding domain-averaged MDA8 O3 concentrations were 122, 126 and 128 µg m−3, respectively. Based on the frequency and intensity changes of the synoptic circulation patterns, 39.2 % of the interannual increase in the domain-averaged O3 from 2013 to 2017 was attributed to synoptic changes, and the intensity of the synoptic circulation patterns was the dominant factor. Using synoptic classification and local meteorological factors, the segmented synoptic-regression approach was established to evaluate and forecast daily ozone variability on an urban scale. The results showed that this method is practical in most cities, and the dominant factors are the maximum temperature, southerly winds, relative humidity on the previous day and on the same day, and total cloud cover. Overall, 41 %–63 % of the day-to-day variability in the MDA8 O3 concentrations was due to local meteorological variations in most cities over northern China, except for two cities: QHD (Qinhuangdao) at 34 % and ZZ (Zhengzhou) at 20 %. Our quantitative exploration of the influence of both synoptic and local meteorological factors on interannual and day-to-day ozone variability will provide a scientific basis for evaluating emission reduction measures that have been implemented by the national and local governments to mitigate air pollution in northern China.
Highlights
Tropospheric ozone (O3) is one of the air pollutants of greatest concern due to its considerable harm to human health and vegetation (Kinney, 2008; Fleming et al, 2018; Mills et al, 2018)
The spatial distribution of the averaged maximum daily 8 h running average O3 (MDA8 O3) concentration (Fig. 1b) and exceedance ratio, which represents the proportion of days exceeding the standard (160 μg m−3) (Fig. 1c), as well as detailed information on the 58 cities (Table S1), showed a severe ozone pollution problem during the last 5 years in northern China
The most polluted cities were concentrated in Beijing, the southeast of Hebei, and the west and north of Shandong, where the average MDA8 O3 concentration was 130 ± 9 μg m−3 and the exceedance ratio was 27.9 ± 7.2 %
Summary
Tropospheric ozone (O3) is one of the air pollutants of greatest concern due to its considerable harm to human health and vegetation (Kinney, 2008; Fleming et al, 2018; Mills et al, 2018). Systematic research aimed at quantifying the evolution of ozone and meteorological impacts and contributions throughout the warm season (April–October) was limited during the 5 years (2013–2017) when the Action Plan for Air Pollution Prevention and Control (http://www.gov.cn/zwgk/2013-09/12/ content_2486773.htm, last access: (9 September 2019) was implemented This lack of analysis has prevented a clear understanding of the effect of emission reduction measures on ozone in northern China from being obtained. In this study, we explore how the maximum daily 8 h running average O3 (MDA8 O3) concentration varies, and we quantify the contributions of synoptic and local meteorological conditions to the ozone variability in northern China (58 cities covering Hebei, Shanxi, Shandong, and Henan provinces and Beijing and Tianjin municipalities) during April–October in 2013–2017. Our specific goals are to (1) demonstrate the characteristics and variation trends in the surface MDA8 O3 concentration; (2) classify the predominant weather types and meteorological mechanisms underlying the regional ozone levels and variability; (3) quantify the contributions of changes in synoptic circulation patterns (frequency and intensity) to the interannual variability in the O3 concentration; and (4) quantify the contributions of local meteorological factors to day-to-day variations in O3 levels and identify the prominent meteorological variables and construct an O3 potential forecast model for major cities
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