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Discussion papers
https://doi.org/10.5194/acp-2018-588
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2018-588
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 30 Oct 2018

Research article | 30 Oct 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Cold fronts – a potential air quality threat over the Yangtze River Delta, China

Hanqing Kang1,2,3,4, Bin Zhu1,2,3,4, Jinhui Gao5, Yao He6, Honglei Wang1,2,3,4, Jifeng Su7, Chen Pan1,2,3,4, Tong Zhu8,9, and Bu Yu10 Hanqing Kang et al.
  • 1Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disaster, Nanjing University of Information Science and Technology, Nanjing, China
  • 2Key Laboratory for Aerosol-Cloud-Precipitation of China Meteorological Administration, Nanjing University of Information Science and Technology, Nanjing, China
  • 3Key Laboratory of Meteorological Disaster, Ministry of Education (KLME), Nanjing University of Information Science and Technology, Nanjing, China
  • 4Joint International Research Laboratory of Climate and Environment Change (ILCEC), Nanjing University of Information Science and Technology, Nanjing, China
  • 5Department of Ocean Science and Engineering, Southern University of Science and Technology, Shenzhen, China
  • 6Baoji Meteorological Bureau, Baoji, China
  • 7The 61 Squad of the 94857 Unit of People's Liberation Army, Wuhu, China
  • 8CIRA, Colorado State University, Fort Collins, Colorado, USA
  • 9NOAA/NESDIS/STAR/JSCDA, College Park, Maryland, USA
  • 10Hangzhou Meteorological Bureau, Hangzhou, China

Abstract. Cold frontal passages usually promote quick removal of atmospheric pollutants over North China (e.g. the Beijing–Tianjin–Hebei region). However, in the Yangtze River Delta (YRD), cold fronts pose a potential threat to air quality. In this study, a cold frontal passage and a subsequent stable weather event over YRD during 21–26 January 2015 was investigated with in-situ observations and Weather Research and Forecasting–Community Multiscale Air Quality Modeling System simulations. Observations showed a burst of PM2.5 pollution and an obvious southward motion of PM2.5 peaks on the afternoon of 21 January, suggesting a strong inflow of highly polluted airmasses to YRD by a cold frontal passage. Model simulations revealed an existing warm and polluted airmass over YRD, which climbed to the free troposphere along the frontal surface as the cold front passed, increasing the PM2.5 concentration at high altitudes. Strong north-westerly flow behind the cold front transported particles from the highly polluted North China Plain (NCP) to YRD. As the cold front intruded into the downstream of YRD, high pressure took control over the YRD, which resulted in a synoptic subsidence that brought particles from the free troposphere (1.0–2.0km) to the surface. After the cold front's passage, weakened winds and a stable atmosphere stayed over the YRD and led to the accumulation of locally emitted PM2.5. Tagging of PM2.5 by geophysical regions showed that the PM2.5 contribution from the YRD itself was 35% and the contribution from the NCP was 29% during the cold frontal passage. However, under the subsequent stable weather conditions, the PM2.5 contribution from the YRD increased to 61.5% and the contribution from the NCP decreased to 14.5%. The results of this study indicate that cold fronts are potential bringers of atmospheric pollutants when there are strong air pollutant sources in upstream areas, which may deteriorate air quality in downstream regions.

Hanqing Kang et al.
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In this study, we found that cold front can deteriorate air quality over Yangtze River Delta (YRD) by bringing air pollutants from the upstream North China Plain (NCP). Warm and polluted airmass in the south edge of the cold front climbed to the free troposphere (1.0–2.0 km) along the frontal surface as the cold front passed. After the cold front's passage, high pressure took control, which resulted in a synoptic subsidence that brought particles from the free troposphere to the surface.
In this study, we found that cold front can deteriorate air quality over Yangtze River Delta...
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