Mixing-layer height retrieval with ceilometer and Doppler lidar: from case studies to long-term assessment

Schween, Jan H.; Hirsikko, Anne; Löhnert, Ulrich; Crewell, Susanne

doi:10.5194/amt-7-3685-2014

Cited by 128 publications

(122 citation statements)

References 58 publications

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“…The profile of attenuated backscattering coefficients in the atmosphere can be analyzed to determine the location of sudden changes caused by variations in the attenuated backscattering coefficients, which is at the top of the atmospheric mixing layer. The lidar ceilometer is inexpensive and convenient and has been widely applied in observations of the mixing-layer height (Sicard et al, 2006;Münkel et al, 2007;McKendry et al, 2009;Emeis et al, 2012;Yang et al, 2013;Pandolfi et al, 2013;Schween et al, 2014;Scarino et al, 2014). In this study, the gradient method was used to identify the mixing-layer height, and maximum negative gradient value (−dβ/dx) of the attenuated backscattering coefficient profile was at the top of the mixing layer (Michael et al, 2006;Emeis et al, 2012).…”

Section: Calculation Of Mixing-layer Heightmentioning

confidence: 99%

Impact of emission controls on air quality in Beijing during APEC 2014: lidar ceilometer observations

et al. 2015

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Abstract. The implementation of emission reductions during the 2014 Asia-Pacific Economic Cooperation (APEC) summit provides a valuable opportunity to study air pollution in Beijing. From 15 October to 30 November 2014, the height of the atmospheric mixing layer and the vertical attenuated backscattering coefficient profiles were observed online using a lidar ceilometer. Compared with fine particulate matter (PM 2.5 ) and aerosol optical depth (AOD) data, the attenuated backscattering coefficients measured by the lidar ceilometer were strongly correlated with the PM 2.5 concentration and AOD (correlation coefficients of 0.89 and 0.86, respectively). This result demonstrated the reliability of the vertical distribution of particles measured by the lidar ceilometer. By classifying different degrees of air pollution based on visibility, we found that during the transition period of air pollution, which was affected by transport of southerly flows in the mixing layer, the attenuated backscattering coefficient from 0 to 1500 m was enhanced by approximately 1.4 Mm −1 sr −1 (140 %). During the polluted period, the attenuated backscattering coefficient from 0 to 300 m suddenly increased, and the coefficient near the surface peaked (approximately 14 Mm −1 sr −1 ); however, the attenuated backscattering coefficient from 300 to 900 m decreased gradually, and the average value from 0 to 1500 m decreased by 0.5 Mm −1 sr −1 (20 %). The height of the mixing layer gradually decreased, and the ratio of CO / SO 2 gradually increased, which indicate that the polluted period was dominated by local contribution. Due to the emission reductions during APEC (DAPEC), the concentration of PM 2.5 decreased by 59.2 and 58.9 % and visibility improved by 70.2 and 56.0 % compared to before (BAPEC) and after APEC (AAPEC), respectively. The contribution of regional transport in DAPEC decreased by approximately 36 and 25 %, and the local contribution decreased by approximately 48 and 54 % compared to BAPEC and AAPEC, respectively. The most effective method of controlling air pollution in the Beijing area is to reduce regional emissions during the transition period and reduce local emissions during the polluted period.

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Section: Calculation Of Mixing-layer Heightmentioning

confidence: 99%

Impact of emission controls on air quality in Beijing during APEC 2014: lidar ceilometer observations

et al. 2015

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“…Ceilometer is a robust, low-power, low-cost and lowmaintenance lidar designed to determine the cloud base height but also provide the backscatter profile, though with less sensitivity than a lidar. Several studies have proposed that ceilometer-measured backscatter profiles can be used to derive the PBL height (Eresmaa et al, 2006(Eresmaa et al, , 2012Münkel, 2007;Haeffelin et al, 2012;Schween et al, 2014). A "structure of the atmosphere" (STRAT-2D) algorithm was selected for estimating the PBL height, which has been proposed in the literature (Morille et al, 2007;Haeffelin et al, 2012;Wiegner et al, 2014).…”

Section: Determination Of the Pbl Heightmentioning

confidence: 99%

Quantifying the relationship between PM<sub>2.5</sub> concentration, visibility and planetary boundary layer height for long-lasting haze and fog–haze mixed events in Beijing

et al. 2018

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Abstract. Air quality and visibility are strongly influenced by aerosol loading, which is driven by meteorological conditions. The quantification of their relationships is critical to understanding the physical and chemical processes and forecasting of the polluted events. We investigated and quantified the relationship between PM 2.5 (particulate matter with aerodynamic diameter is 2.5 µm and less) mass concentration, visibility and planetary boundary layer (PBL) height in this study based on the data obtained from four long-lasting haze events and seven fog-haze mixed events from January 2014 to March 2015 in Beijing. The statistical results show that there was a negative exponential function between the visibility and the PM 2.5 mass concentration for both haze and fog-haze mixed events (with the same R 2 of 0.80). However, the fog-haze events caused a more obvious decrease of visibility than that for haze events due to the formation of fog droplets that could induce higher light extinction. The PM 2.5 concentration had an inversely linear correlation with PBL height for haze events and a negative exponential correlation for fog-haze mixed events, indicating that the PM 2.5 concentration is more sensitive to PBL height in fog-haze mixed events. The visibility had positively linear correlation with the PBL height with an R 2 of 0.35 in haze events and positive exponential correlation with an R 2 of 0.56 in foghaze mixed events. We also investigated the physical mechanism responsible for these relationships between visibility, PM 2.5 concentration and PBL height through typical haze and fog-haze mixed event and found that a double inversion layer formed in both typical events and played critical roles in maintaining and enhancing the long-lasting polluted events. The variations of the double inversion layers were closely associated with the processes of long-wave radiation cooling in the nighttime and short-wave solar radiation reduction in the daytime. The upper-level stable inversion layer was formed by the persistent warm and humid southwestern airflow, while the low-level inversion layer was initially produced by the surface long-wave radiation cooling in the nighttime and maintained by the reduction of surface solar radiation in the daytime. The obvious descending process of the upper-level inversion layer induced by the radiation process could be responsible for the enhancement of the lowlevel inversion layer and the lowering PBL height, as well as high aerosol loading for these polluted events. The reduction of surface solar radiation in the daytime could be around 35 % for the haze event and 94 % for the fog-haze mixed event. Therefore, the formation and subsequent descending processes of the upper-level inversion layer should be an important factor in maintaining and strengthening the longlasting severe polluted events, which has not been revealed in previous publications. The interactions and feedbacks between PM 2.5 concentration and PBL height linked by radiation process caused a more significant an...

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“…The continuous monitoring of the atmospheric mixing profile covering the lowest few kilometres is not a straightforward task and there are only a few long-term data sets (e.g. Harvey et al, 2013;Schween et al, 2014). In many studies the mixed layer is characterised indirectly, often in terms of MLH inferred from aerosol backscatter profiles (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…However, indirect methods in MLH estimation may potentially suffer from erroneous interpretation, especially for stably stratified layers and during the initial early morning phase or afternoon collapse of a convective boundary layer (e.g. Pearson et al, 2010;Schween et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

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Low-level mixing height detection in coastal locations with a scanning Doppler lidar

et al. 2015

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Abstract. Mixing layer height (MLH) is one of the key parameters in describing lower tropospheric dynamics and capturing its diurnal variability is crucial, especially for interpreting surface observations. In this paper we introduce a method for identifying MLH below the minimum range of a scanning Doppler lidar when operated at vertical. The method we propose is based on velocity variance in lowelevation-angle conical scanning and is applied to measurements in two very different coastal environments: Limassol, Cyprus, during summer and Loviisa, Finland, during winter. At both locations, the new method agrees well with MLH derived from turbulent kinetic energy dissipation rate profiles obtained from vertically pointing measurements. The lowlevel scanning routine frequently indicated non-zero MLH less than 100 m above the surface. Such low MLHs were more common in wintertime Loviisa on the Baltic Sea coast than during summertime in Mediterranean Limassol.

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Mixing-layer height retrieval with ceilometer and Doppler lidar: from case studies to long-term assessment

Cited by 128 publications

References 58 publications

Impact of emission controls on air quality in Beijing during APEC 2014: lidar ceilometer observations

Impact of emission controls on air quality in Beijing during APEC 2014: lidar ceilometer observations

Quantifying the relationship between PM<sub>2.5</sub> concentration, visibility and planetary boundary layer height for long-lasting haze and fog–haze mixed events in Beijing

Low-level mixing height detection in coastal locations with a scanning Doppler lidar

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Mixing-layer height retrieval with ceilometer and Doppler lidar: from case studies to long-term assessment

Cited by 128 publications

References 58 publications

Impact of emission controls on air quality in Beijing during APEC 2014: lidar ceilometer observations

Impact of emission controls on air quality in Beijing during APEC 2014: lidar ceilometer observations

Quantifying the relationship between PM&lt;sub&gt;2.5&lt;/sub&gt; concentration, visibility and planetary boundary layer height for long-lasting haze and fog–haze mixed events in Beijing

Low-level mixing height detection in coastal locations with a scanning Doppler lidar

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Quantifying the relationship between PM<sub>2.5</sub> concentration, visibility and planetary boundary layer height for long-lasting haze and fog–haze mixed events in Beijing