the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
05 Jan 2021
05 Jan 2021
Warm Cover
– Precursory Strong Signals
hidden in the Middle
Troposphere for Haze Pollution
- 1State Key Laboratory of Severe Weather (LASW), Chinese Academy of Meteorological Sciences, Beijing, China
- 2National Climate Center, China Meteorological Administration, Beijing, China
- 3School of Geographical Science, Nanjing University of Information Science and Technology, Nanjing, Jiangsu Province, China
- 4Key Laboratory for Aerosol-Cloud-Precipitation of China Meteorological Administration, Nanjing University of Information Science and Technology, Nanjing, Jiangsu Province, China
- 5School of Applied Meteorology, Nanjing University of Information Science and Technology, Nanjing, Jiangsu Province, China
- 6Beijing Institute of Applied Meteorology, Beijing, China
- 7Meteorological Observation Center, China Meteorological Administration, Beijing, China
- 8Training Center, China Meteorological Administration, Beijing, China
- 9School of Atmospheric Sciences/Plateau Atmosphere and Environment Key Laboratory of Sichuan Province/Joint Laboratory of Climate and Environment Change, Chengdu University of Information Technology, Chengdu, Sichuan Province, China
- 1State Key Laboratory of Severe Weather (LASW), Chinese Academy of Meteorological Sciences, Beijing, China
- 2National Climate Center, China Meteorological Administration, Beijing, China
- 3School of Geographical Science, Nanjing University of Information Science and Technology, Nanjing, Jiangsu Province, China
- 4Key Laboratory for Aerosol-Cloud-Precipitation of China Meteorological Administration, Nanjing University of Information Science and Technology, Nanjing, Jiangsu Province, China
- 5School of Applied Meteorology, Nanjing University of Information Science and Technology, Nanjing, Jiangsu Province, China
- 6Beijing Institute of Applied Meteorology, Beijing, China
- 7Meteorological Observation Center, China Meteorological Administration, Beijing, China
- 8Training Center, China Meteorological Administration, Beijing, China
- 9School of Atmospheric Sciences/Plateau Atmosphere and Environment Key Laboratory of Sichuan Province/Joint Laboratory of Climate and Environment Change, Chengdu University of Information Technology, Chengdu, Sichuan Province, China
Abstract. Eastern China (EC), located on the downstream region of Tibetan Plateau (TP), is a large area that has become vulnerable to frequent haze. In addition of air pollutant emissions, meteorological conditions were a key inducement
for air pollution episodes. Based on the study of the Great Smog of London in 1952 and haze pollution in EC over recent decades, it is found that the abnormal warm cover
in the middle troposphere, as a precursory strong signal
hidden, could connect to severe air pollution events. The convection and diffusion in the atmospheric boundary layer (ABL) were suppressed by a relatively stable structure of warm cover
in the middle troposphere, leading to the ABL height decreases, which were favourable for the accumulation of air pollutants in the ambient atmosphere. The warming TP built the warm cover
in the middle troposphere from the plateau to the downstream EC region and even the entire East Asian region. The frequent haze events in EC is connected with a significantly strong warm cover
in the interdecadal variability. It is also revealed that a close relationship existed between interannual variations of the TP's heat source and the warm cover
hidden in the middle troposphere over EC.
Warm Cover– Precursory
Strong Signalshidden in the Middle Troposphere for Haze Pollution, Atmos. Chem. Phys. Discuss. [preprint], https://doi.org/10.5194/acp-2020-1140, in review, 2021.
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Xiangde Xu et al.
Status: open (extended)
-
RC1: 'Comment on acp-2020-1140', Anonymous Referee #1, 27 Feb 2021
reply
This work proposed that abnormal ‘warm cover’ in the middle troposphere could suppress the convection and diffusion in the boundary layer, leading to haze pollution in Eastern China. It is also indicated that such ‘warm cover’ is attributed to the warming of the Tibetan Plateau. I think this work well fits the scope of this journal. Overall, this manuscript is well structured but needs more in-depth analysis to further improve this article. Besides, the writing needs to be polished. It is worth being published after addressing the following issues.
Major comments
The introduction is too simple and is not sufficient to clearly demonstrate the background and scientific significance of this work. Pre-existing literature on this subject is suggested to be fully reviewed, and a comprehensive introduction ought to be provided in this part.
The Great Smog of London in 1952 is one of the most well-known air pollution events across the world. Comparatively speaking, the haze in the North China Plain in February 2014 is not that "eye-catching". Why chose this pollution episode for comparison? 2013 Beijing Haze has drawn more attention from both scientific research and public concern.
It is plausible that 'Warm Cover' may intensify the haze pollution in Eastern China, theoretically. However, as mentioned by the authors, the thermodynamical structure is closely related to circulation, which can significantly influence the regional transport/ventilation of air pollutants. It needs to be clarified whether the anomalous circulation or thermodynamical structure (ABL height decrease) is the main cause of haze pollution. This work only provides correlation and cross-sections of temperature anomalies and PM2.5 concentration, both of which are a little too descriptive. More in-depth discussion and some quantitative analysis are suggested to be provided.
The writing needs to be polished by language editing to improve the overall readability.
Minor comments
Line 26: "In addition to"
Line 43: Delete "with excessive concentrations of PM2. 5"
Line 87: the North China Plain. Please check it throughout the manuscript.
Line 88-89: Change to "for the long-lasting and heavy haze pollution". This statement needs to be rephrased. "sulfur-dioxide pollutants” is not appropriate.
Line 98: What do you mean by "long heavy air pollution "?
The labels in the contour plot in Fig.3-4 are overlaid and need to be optimized.
All the abbreviations should be defined for the first time. Please check throughout the article.
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AC1: 'Reply on RC1', Wenyue Cai, 08 Mar 2021
reply
Major comments:
1. For the introduction, we have adjusted it as required and added new content.
“1 Introduction
In China, mainly over the region east of 100°E and south of 40°N (Tie et al., 2009), PM2.5 (particulate matter with an aerodynamic diameter equal to or less than 2.5 μm) has become the primary air pollutant (Wang, et al., 2017). Therefore，in September 2013, the Chinese government launched the China's first air pollution control action plan – ‘The Airborne Pollution Prevention and Control Action Plan (2013-2017)’ (State Council of the People’s Republic of China, 2013). By 2017, 64% of China’s cities are still suffering from the air pollution, especially Beijing-Tianjin-Hebei region and surrounding areas (Wang et al., 2019; Miao et al., 2019). Then, in July 2018, the Chinese government launched the second three-year action plan for air pollution control, the "blue sky defense plan", which demonstrates China's firm determination and new measures for air pollution control (State Council of the People’s Republic of China, 2018). After the implementation of air pollution control action plans, the air quality in many regions and cities in China has been significantly improved.
Anthropogenic pollutant emissions and unfavorable meteorological conditions are commonly regarded as two key factors for haze pollution(Ding and Liu, 2014; Yim et al., 2014; Zhang et al., 2015). Air pollutants mainly come from the surface emission sources, and most of the pollutants are transported from the surface to the atmosphere through the atmospheric boundary layer (ABL) (Quan et al., 2020). Structural characteristics of ABL are the key meteorological conditions which influences the formation and maintenance of heavy pollution episodes (Wang et al., 2015; Cheng et al., 2016; Wang et al., 2016; Tang et al., 2016; Wang et al., 2019).
Most of the previous studies focused on exploring the impact on the heavy air pollution in Eastern China (EC) for the meteorological conditions in ABL. However, the thermodynamic and dynamic structures of troposphere can affect the meteorological conditions in ABL (Cai et al., 2020). The convection and diffusion in the ABL were suppressed by a relatively stable structure of ‘warm cover’ in the middle troposphere, leading to the ABL height decreases, which were favourable for the formation and persistence of heavily polluted weather (Quan et al.,2013; Wang et al.,2015; Cai et al., 2020).
This study investigated whether the thermodynamic structure of the troposphere and its intensity changes can be used as a "strong warning signal" for the changes of PM2.5 concentration in heavily polluted weathers, and whether this strong signal exists in the time scales of seasonal, interannual and interdecadal. In order to explore the interaction between the free troposphere and the ABL and the impact on the heavy air pollution in Eastern China (EC), this study extended the meteorological conditions for heavy air pollution from the boundary layer to the middle troposphere. We identify a precursory ‘strong signals’ hidden in the free troposphere for frequent haze pollution in winter in EC. ”
2. Meteorological conditions in February 2014 were worse than that in January 2013. In February 2014，a rarely persistent air pollution weather process occurred in central and eastern China, this process had caused severe air pollution in more than 50 cities, with an impact area of 2.07 million square kilometers. Among the 25 regional ultra-long pollution events (≥6 days) during the winters of 2012–2018, the ‘most serious’ pollution events during February 18–27 was long lasting, contained heavy pollution, produced low visibility, and had a broad impact on northern China. In the Beijing area during February 20–26, the regional average PM2.5 concentration was continued to exceed the ‘most-serious’ pollution level, and with a peak value of up to 456 µg m-3.
3. Due to the limited space of the article, some quantitative analysis will be given in the future, such as the contribution of each meteorological element to polluted weather. This study focused on exploring whether the thermodynamic structure of the troposphere and its intensity changes can be used as a "strong warning signal" for the changes of PM2.5 concentration in heavily polluted weathers, and whether this strong signal exists in the time scales of seasonal, interannual and interdecadal.
Minor comments:
- Line 26: "In addition to". We have adjusted it as required.
- Line 43: Delete "with excessive concentrations of PM 2.5". We have adjusted it as required.
- Line 87: the North China Plain. Please check it throughout the manuscript. We have removed it.
- Line 88-89: Change to "for the long-lasting and heavy haze pollution". This statement needs to be rephrased. "sulfur-dioxide pollutants” is not appropriate. We have adjusted it as required.
- Line 98: What do you mean by "long heavy air pollution "? We have adjusted it as required, "persistent heavy air pollution".
- The labels in the contour plot in Fig.3-4 are overlaid and need to be optimized. We have adjusted it as required.
- All the abbreviations should be defined for the first time. Please check throughout the article. We have adjusted it as required.
-
AC1: 'Reply on RC1', Wenyue Cai, 08 Mar 2021
reply
Xiangde Xu et al.
Xiangde Xu et al.
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strong forewarning signalfor the variations of surface PM2.5 concentration in heavy air pollution.