Vertical observation and analysis on rapid formation and evolutionary mechanisms of a prolonged haze episode over central-eastern China

Si, Han; Hao, Tianyi; Zhang, Yufen; Liu, Jing-le; Pei-yan, LI; Cai, Zhiqiang; Zhang, Min; Wang, Qin-liang; Zhang, Hao

doi:10.1016/j.scitotenv.2017.10.278

Cited by 50 publications

(29 citation statements)

References 28 publications

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“…suggested that the high concentration of particles in the residual layer could reach the ground the following morning through convection, causing severe pollutant concentrations in Beijing. In the Tianjin area, Han et al (2018) also found that a pollution layer was present at the altitude of 1000 m in the early morning on 16 December, 2016, where the aerosols in the higher layers were transmitted to the ground by downward flow before the formation of heavy pollution. Actually, many studies have focused on this mechanism of pollutant vertical mixing in a stable NBL from the micrometeorology perspective.…”

Section: Development Of the Ublmentioning

confidence: 92%

“…The main hazards or negative effects of air pollution generally fall into two categories: human health and transportation. Thus, it is an issue that has attracted considerable public attention and, accordingly, numerous studies have focused on investigating the sources and formation mechanisms of air pollution in the BTH region, through numerical simulation and field observational methods (e.g., Sun et al, 2014;Ye et al, 2016;Han et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

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Observations of the atmospheric boundary layer structure over Beijing urban area during air pollution episodes

Wang¹,

Liu²,

Gao³

et al. 2019

Preprint

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Abstract. We investigated the interactions between the air pollutants and the structure of urban boundary layer (UBL) over Beijing by using the data mainly obtained from the 325-m meteorological tower and a Doppler wind lidar during 1&#8211;4 December, 2016. Results showed that the pollution episodes in this period could be characterized by low surface pressure, high relative humidity, weak wind, and temperature inversion. Compared with a clean daytime episode that took place on 1 December, results also showed that the attenuation ratio of downward shortwave radiation was about 4&#8201;%, 23&#8201;% and 78&#8201;% at 1200 local standard time (LST) on 2&#8211;4 December respectively, while for the net radiation (Rn) attenuation ratio at the 140-m level of the 325-m tower was 2&#8201;%, 24&#8201;%, and 86&#8201;%. The large reduction in Rn on 4 December was not only the result of the aerosols, but also clouds. Based on analysis of the surface energy balance at the 140-m level, we found that the sensible heat flux was remarkably diminished during daytimes on polluted days, and even negative after sunrise (about 0720 LST) till 1400 LST on 4 December. We also found that heat storage in the urban surface layer played an important role in the exchange of the sensible heat flux. Owing to the advantages of the wind lidar having superior spatial and temporal resolution, the vertical velocity variance could capture the evolution of the UBL well. It clearly showed that weak vertical mixing caused the concentrating of pollutants, and that vertical mixing would also be weakened by a certain quantity of pollutants, and then in turn worsened the pollution further. Compared to the clean daytime on 1 December, the maximums of the boundary layer height (BLH) reduced about 44&#8201;% and 56&#8201;% on 2&#8211;3 December, when the average PM2.5 (PM1) concentrations in afternoon hours (from 1200 to 1400 LST) were 44 (48)&#8201;&#181;g&#8201;m&#8722;3 and 150 (120)&#8201;&#181;g&#8201;m&#8722;3 . Part of these reductions of the BLH was also contributed by the effect of the heat storage in the urban canopy.

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Section: Development Of the Ublmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Observations of the atmospheric boundary layer structure over Beijing urban area during air pollution episodes

Wang¹,

Liu²,

Gao³

et al. 2019

Preprint

View full text Add to dashboard Cite

show abstract

“…illustrated these levels were accumulated with high levels of pollutants and the vertical distribution of pollutants was inhomogeneous, all of which implies that the 260 m level may have been in the residual layer. The pollutants in the resid-ual layer are known to play an important role in the diurnal changes of pollutants at the surface (Hastie et al, 1993;Berkowitz et al, 2000;Salmond and Mckendary, 2006). Sun et al (2013) suggested that the high concentration of particles in the residual layer could reach the ground the following morning through convection, causing severe pollutant concentrations in Beijing.…”

Section: Development Of the Ublmentioning

confidence: 99%

Vertical observations of the atmospheric boundary layer structure over Beijing urban area during air pollution episodes

et al. 2019

View full text Add to dashboard Cite

Abstract. We investigated the interactions between the air pollutants and the structure of the urban boundary layer (UBL) over Beijing by using the data mainly obtained from the 325 m meteorological tower and a Doppler wind lidar during 1–4 December 2016. Results showed that the pollution episodes in this period could be characterized by low surface pressure, high relative humidity, weak wind, and temperature inversion. Compared with a clean daytime episode that took place on 1 December, results also showed that the attenuation ratio of downward shortwave radiation was about 5 %, 24 % and 63 % in afternoon hours (from 12:00 to 14:00 local standard time, LST) on 2–4 December, respectively, while for the net radiation (Rn) attenuation ratio at the 140 m level of the 325 m tower was 3 %, 27 % and 68 %. The large reduction in Rn on 4 December was not only the result of the aerosols, but also clouds. Based on analysis of the surface energy balance at the 140 m level, we found that the sensible heat flux was remarkably diminished during daytime on polluted days and even negative after sunrise (about 07:20 LST) till 14:00 LST on 4 December. We also found that heat storage in the urban surface layer played an important role in the exchange of the sensible heat flux. Owing to the advantages of the wind lidar having superior spatial and temporal resolution, the vertical velocity variance could capture the evolution of the UBL well. It clearly showed that vertical mixing was negatively related to the concentrating of pollutants, and that vertical mixing would also be weakened by a certain quantity of pollutants, and then in turn worsened the pollution further. Compared to the clean daytime on 1 December, the maximums of the boundary layer height (BLH) decreased about 44 % and 56 % on 2–3 December, when the average PM2.5 (PM1) concentrations in afternoon hours (from 12:00 to 14:00 LST) were 44 (48) µg m−3 and 150 (120) µg m−3. Part of these reductions of the BLH was also contributed by the effect of the heat storage in the urban canopy.

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“…11. Elevated polluted air has been observed in the Beijing area (e.g., Han et al, 2018); the advection process is commonly believed to be the transporting mechanism. This study demonstrates that turbulent mixing in the PBL plays an important role in direct transporting polluted air and in determining effectiveness of horizontal advection of polluted air.…”

Section: Discussionmentioning

confidence: 99%

Observational analyses of dramatic developments of a severe air pollution event in the Beijing area

Sun

Zhou

et al. 2018

Atmos. Chem. Phys.

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Abstract. A rapid development of a severe air pollution event in Beijing, China, at the end of November 2015 was investigated with unprecedented observations collected during the field campaign of the Study of Urban Rainfall and Fog/Haze (SURF-15). Different from previous statistical analyses of air pollution events and their correlations with meteorological environmental conditions in the area, the role of turbulent mixing in the pollutant transfer was investigated in detail. The analyses indicate that the major pollution source associated with high particulate matter of diameter 2.5 µm (PM2.5) was from south of Beijing. Before the day of the dramatic PM2.5 increase, the nighttime downslope flow from the mountains to the west and north of Beijing reduced the surface PM2.5 concentration northwest of Beijing. The nighttime surface stable boundary layer (SBL) not only kept the relatively less-polluted air near the surface, it also shielded the rough surface from the pollutant transfer by southwesterly winds above the SBL, leading to the fast transport of pollutants over the Beijing area at night. As the daytime convective turbulent mixing developed in the morning, turbulent mixing transported the elevated polluted air downward even though the weak surface wind was from northeast, leading to the dramatic increase of the surface PM2.5 concentration in the urban area. As a result of both turbulent mixing and advection processes with possible aerosol growth from secondary aerosol formation under the low-wind and high-humidity conditions, the PM2.5 concentration reached over 700 µg m−3 in the Beijing area by the end of the day. Contributions of the two transporting processes to the PM2.5 oscillations prior to this dramatic event were also analyzed. The study demonstrates the important role of large-eddy convective turbulent mixing in vertical transfer of pollutants and the role of the SBL in not only decoupling vertical transport of trace gases and aerosols but also in accelerating horizontal transfer of pollutants above.

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Vertical observation and analysis on rapid formation and evolutionary mechanisms of a prolonged haze episode over central-eastern China

Cited by 50 publications

References 28 publications

Observations of the atmospheric boundary layer structure over Beijing urban area during air pollution episodes

Observations of the atmospheric boundary layer structure over Beijing urban area during air pollution episodes

Vertical observations of the atmospheric boundary layer structure over Beijing urban area during air pollution episodes

Observational analyses of dramatic developments of a severe air pollution event in the Beijing area

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