An examination of boundary layer structure under the influence of the gap winds in Urumqi, China, during air pollution episode in winter

Li, Xia; Xia, Xiangao; Xin, Yu; Ma, Yufen; Yang, Jing; Li, Jinglin; Yang, Xinghua

doi:10.1080/10473289.2011.617628

Cited by 15 publications

(14 citation statements)

References 15 publications

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“…Similar situations with significant wind direction change in the vertical profile and weak wind speed were presented e.g. in Vergeiner (2004) and Li et al (2012Li et al ( , 2015 for mountain valleys, during hydraulic jump occurrence. In the upper layer, wind direction is constant, while wind speed increases with height.…”

Section: Type IIIsupporting

confidence: 71%

“…The occurrence of a multi-layer vertical structure in the boundary layer was noticed during the foehn periods, too, where warm air advection caused the intensification of the air temperature inversion and CAP and reduction of the available air volume for mixing the pollutants (e.g. sandwich foehn occurrence : Vergeiner, 2004;Drechsel and Mayr, 2008;Li et al, 2015). In the present paper, for the days with balloon flights, the occurrence of PM 10 profile type III was connected with the advection of air masses from the south.…”

Section: Discussionsupporting

confidence: 50%

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Measurement report: Effect of wind shear on PM10 concentration vertical structure in the urban boundary layer in a complex terrain

et al. 2021

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Abstract. The paper shows wind shear impact on PM10 vertical profiles in Kraków, southern Poland. The data used consist of background data for two cold seasons (September 2018 to April 2019 and September 2019 to April 2020) and data for several case studies from November 2019 to March 2020. The data are composed of PM10 measurements, model data, and wind speed and direction data. The background model data come from operational forecast results of the AROME model. PM10 concentration in the vertical profile was measured with a sightseeing balloon. Significant spatial variability of the wind field was found. The case studies represent the conditions with much lower wind speed and a much higher PM10 level than the seasonal average. The inversions were much more frequent than on average too. Wind shear turned out to be the important factor in terms of PM10 vertical profile modification. It is generated due to the relief impact, i.e. the presence of a large valley, blocked on one side with the hills. The analysis of PM10 profiles from all flights allows us to distinguish three vertical zones of potential air pollution hazards within the valley (about 100 m deep) and the city of Kraków: (1) up to about 60 m a.g.l. – the zone where during periods of low wind speed, air pollution is potentially the highest and the duration of such high levels is the longest, i.e. the zone with the worst aerosanitary conditions; (2) about 60–100 m a.g.l. – transitional zone where the large decrease in PM10 levels with height is observed; (3) above 100–120 m a.g.l. – the zone where air quality is significantly better than in zone 1, either due to the increase in the wind speed or due to the wind direction change and advection of different, clean air masses.

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Section: Type IIIsupporting

confidence: 71%

Section: Discussionsupporting

confidence: 50%

Measurement report: Effect of wind shear on PM10 concentration vertical structure in the urban boundary layer in a complex terrain

et al. 2021

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“…presented at e.g. Vergeiner, 2004, Li X. et al, 2012and Li et al 2015, for mountain valleys, during hydraulic jump occurrence. In the upper layer, wind direction is constant while wind speed increases with height.…”

Section: Type IIImentioning

confidence: 99%

“…black carbon (Zhou et al, 2020) or organic PM10 tracers like levoglucosan (Marynowski et al, 2020). Numerous studies indicate that an important factor that affects the pollution profile is the wind profile (Li and Han, 2016;Zhou et al, 2020), occurrence of low-level jet (Li et al, 2012;Li et al, 2019) or downward flows of pollutants (Han et al, 2018) which may strongly modify diurnal cycle of a pollutant concentration at the lowest part of the troposphere.…”

Section: Introductionmentioning

confidence: 99%

Measurement report: Effect of wind shear on PM10 concentration vertical structure in urban boundary layer in a complex terrain

Sekula¹,

Bokwa²,

Bartyzel³

et al. 2021

Preprint

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Abstract. The paper shows wind shear impact on PM10 vertical profiles, in Kraków, southern Poland. The data used consist of background data for two cold seasons (Sep. 2018 to Apr. 2019, and Sep. 2019 to Apr. 2020), and data for several case studies from November 2019 to March 2020. The data is composed of PM10 measurements, model data, and wind speed and direction data. The background model data come from operational forecast results of AROME model. PM10 concentration in the vertical profile was measured with a sightseeing balloon. Significant spatial variability of wind field was found. The case studies represent the conditions with much lower wind speed and a much higher PM10 levels than the seasonal average. The inversions were much more frequent than on average, too. Wind shear turned out to be the most important factor in terms of PM10 vertical profile modification. It is generated due to the relief impact, i.e. the presence of a large valley, blocked on one side with the hills. The analysis of PM10 profiles from all flights allows to distinguish three vertical zones of potential air pollution hazard within the valley (about 100 m deep) and the city of Kraków: 1. up to about 60 m a.g.l. – the zone where during periods of low wind speed, air pollution is potentially the highest and the duration of such high levels is the longest, i.e. the zone with the worst aerosanitary conditions; 2. about 60–100 m a.g.l. – transitional zone where the large decrease of PM10 levels with height is observed; 3. above 100–120 m a.g.l. – the zone where air quality is significantly better than in the zone 1, either due to the increase of the wind speed, or due to the wind direction change and advection of different, clean air masses.

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“…Such a process was simulated by Li et al . [], in which a strong foehn rushes downward on the lee side of the mountain and simultaneously generates a hydraulic jump and downslope wind around Urumqi. The foehn flow near the surface flushes further down valley.…”

Section: Surface Temperature and Wind Fields Influenced By The Sandwimentioning

confidence: 99%

The role of foehn in the formation of heavy air pollution events in Urumqi, China

Xia

Wang

et al. 2015

JGR Atmospheres

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The impact of sandwich foehn on air pollution in Urumqi, a gap town located on the northern lee side of the Tianshan Mountains of China, is analyzed. The results show that during days with high pollution, the boundary layer over the city and the down-valley area can be divided into a three-layer structure, with the southeasterly foehn sandwiched between the northwesterly winds on top and the cold air surface pool beneath. The southeasterly foehn at heights between 480 and 2100 m results in a very stable boundary layer structure. In combination with the decoupling between the foehn flow and cold air pool, such boundary layer structure prevents vertical mixing of atmospheric pollutants. In the up-valley area from the northern lee side flank to the southern urban area, the ground-based foehn confronts the thermally driven valley breeze and forms a "minifront," which moves northward in the morning and retreats southward in the afternoon. Although the minifront disappears in the early evening, the wind shear of the mountain breeze between the southern suburb and downtown areas is still remarkable, which is favorable for a convergence line to persist around the city all day long. In this case, air pollutants emitted from the up-valley and down-valley areas are transported toward the urban area. Therefore, the air pollutants accumulate daily, leading to the frequent occurrence of heavy pollution events in Urumqi. This indicates that the sandwich foehn plays a critical role in the formation of heavy air pollution events in Urumqi.

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An examination of boundary layer structure under the influence of the gap winds in Urumqi, China, during air pollution episode in winter

Cited by 15 publications

References 15 publications

Measurement report: Effect of wind shear on PM<sub>10</sub> concentration vertical structure in the urban boundary layer in a complex terrain

Measurement report: Effect of wind shear on PM<sub>10</sub> concentration vertical structure in the urban boundary layer in a complex terrain

Measurement report: Effect of wind shear on PM<sub>10</sub> concentration vertical structure in urban boundary layer in a complex terrain

The role of foehn in the formation of heavy air pollution events in Urumqi, China

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An examination of boundary layer structure under the influence of the gap winds in Urumqi, China, during air pollution episode in winter

Cited by 15 publications

References 15 publications

Measurement report: Effect of wind shear on PM&lt;sub&gt;10&lt;/sub&gt; concentration vertical structure in the urban boundary layer in a complex terrain

Measurement report: Effect of wind shear on PM&lt;sub&gt;10&lt;/sub&gt; concentration vertical structure in the urban boundary layer in a complex terrain

Measurement report: Effect of wind shear on PM&lt;sub&gt;10&lt;/sub&gt; concentration vertical structure in urban boundary layer in a complex terrain

The role of foehn in the formation of heavy air pollution events in Urumqi, China

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Measurement report: Effect of wind shear on PM<sub>10</sub> concentration vertical structure in the urban boundary layer in a complex terrain

Measurement report: Effect of wind shear on PM<sub>10</sub> concentration vertical structure in the urban boundary layer in a complex terrain

Measurement report: Effect of wind shear on PM<sub>10</sub> concentration vertical structure in urban boundary layer in a complex terrain