Mixing layer height and air pollution levels in urban area

2012 ◽  
Author(s):  
Klaus Schäfer ◽  
Patrick Wagner ◽  
Stefan Emeis ◽  
Carsten Jahn ◽  
Christoph Muenkel ◽  
...  
Keyword(s):  
Air Pollution ◽  
Urban Area ◽  
Mixing Layer ◽  
Layer Height ◽  
Pollution Levels ◽  
Mixing Layer Height

scholarly journals Boundary Layer Characteristics over the Central Area of the Kathmandu Valley as Revealed by Sodar Observation

2015 ◽  
Vol 20 (1) ◽  
pp. 28-35
Author(s):  
Sajan Shrestha ◽  
Saraswati Shrestha ◽  
Sangeeta Maharjan ◽  
Ram P. Regmi
Keyword(s):  
Boundary Layer ◽  
Air Pollution ◽  
Diurnal Variation ◽  
Mixing Layer ◽  
Central Area ◽  
Kathmandu Valley ◽  
Pollution Dispersion ◽  
Easterly Wind ◽  
Layer Height ◽  
Mixing Layer Height

The characteristic behavior of prevailing boundary layer over the central area of the Kathmandu valley was continuously monitored by deploying a monostatic flat array sodar during the period of 03 to 16 March 2013. Diurnal variation of wind and mixing layer height were chosen to describe the boundary layer activities over the area by considering the day of 12 March 2013 as the representative day for the period of observation. The study shows that central area of the valley remains calm or windless under stable stratification throughout the night and early morning frequently capped by northeasterly or easterly wind aloft. Strong surface level thermal inversion prevails during the period up to the height of 80m above the surface. This inversion tends to lift up as the morning progresses and reaches to the height of 875 m or so close to the noontime. Intrusion of regional winds as westerly/northwesterly and the southerly/southwesterly from the western and southwestern low-mountain passes and the river gorge in the afternoon tends to reduce the noontime mixing layer height to about 700 m. The diurnal variation of wind and mixing layer height suggest that Kathmandu valley possesses a poor air pollution dispersion power and hence the valley is predisposed to high air pollution potential.Journal of Institute of Science and Technology, 2015, 20(1): 28-35

scholarly journals Detailed Assessment of the Effects of Meteorological Conditions on PM10 Concentrations in the Northeastern Part of the Czech Republic

Atmosphere ◽  
2020 ◽  
Vol 11 (5) ◽  
pp. 497 ◽  
Author(s):  
Vladimíra Volná ◽  
Daniel Hladký
Keyword(s):  
Air Pollution ◽  
Wind Direction ◽  
Mixing Layer ◽  
Meteorological Conditions ◽  
Pollution Sources ◽  
Pollution Level ◽  
Layer Height ◽  
Wind Speeds ◽  
Average Maximum ◽  
Mixing Layer Height

This article assessed the links between PM10 pollution and meteorological conditions over the Czech-Polish border area at the Třinec-Kosmos and Věřňovice sites often burdened with high air pollution covering the years 2016–2019. For this purpose, the results of the measurements of special systems (ceilometers) that monitor the atmospheric boundary layer were used in the analysis. Meteorological conditions, including the mixing layer height (MLH), undoubtedly influence the air pollution level. Combinations of meteorological conditions and their influence on PM10 concentrations also vary, depending on the pollution sources of a certain area and the geographical conditions of the monitoring site. Gen1erally, the worst dispersion conditions for the PM10 air pollution level occur at low air temperatures, low wind speed, and low height of the mixing layer along with a wind direction from areas with a higher accumulation of pollution sources. The average PM10 concentrations at temperatures below 1 °C reach the highest values on the occurrence of a mixing layer height of up to 400 m at both sites. The influence of a rising height of the mixing layer at temperatures below 1 °C on the average PM10 concentrations at Třinec-Kosmos site is not as significant as in the case of Věřňovice, where a difference of several tens of µg·m−3 in the average PM10 concentrations was observed between levels of up to 200 m and levels of 200–300 m. The average PM10 hourly concentrations at Třinec-Kosmos were the highest at wind speeds of up to 0.5 m·s−1, at MLH levels of up to almost 600 m; at Věřňovice, the influence of wind speeds of up to 2 m·s−1 was detected. Despite the fact that the most frequent PM10 contributions come to the Třinec-Kosmos site from the SE direction, the average maximum concentration contributions come from the W–N sectors at low wind speeds and MLHs of up to 400 m. In Věřňovice, regardless of the prevailing SW wind direction, sources in the NE–E sector from the site have a crucial influence on the air pollution level caused by PM10.

scholarly journals Determination and climatology of the diurnal cycle of the atmospheric mixing layer height over Beijing 2013–2018: lidar measurements and implications for air pollution

2020 ◽  
Vol 20 (14) ◽  
pp. 8839-8854 ◽  
Author(s):  
Haofei Wang ◽  
Zhengqiang Li ◽  
Yang Lv ◽  
Ying Zhang ◽  
Hua Xu ◽  
...  
Keyword(s):  
Air Pollution ◽  
Diurnal Cycle ◽  
Mixing Layer ◽  
Daily Maximum ◽  
Layer Height ◽  
Stable Conditions ◽  
Lidar Measurements ◽  
Significant Phenomenon ◽  
Mixing Layer Height ◽  
Convective Layer

Abstract. The atmospheric mixing layer height (MLH) determines the space in which pollutants diffuse and is thus conducive to the estimation of the pollutant concentration near the surface. The study evaluates the capability of lidar to describe the evolution of the atmospheric mixing layer and then presents a long-term observed climatology of the MLH diurnal cycle. Detection of the mixing layer heights (MLHL and MLHL′) using the wavelet method based on lidar observations was conducted from January 2013 to December 2018 in the Beijing urban area. The two dataset results are compared with radiosonde as case studies and statistical forms. MLHL shows good performance in calculating the convective layer height in the daytime and the residual layer height at night. While MLHL′ has the potential to describe the stable layer height at night, the performance is limited due to the high range gate of lidar. A nearly 6-year climatology for the diurnal cycle of the MLH is calculated for convective and stable conditions using the dataset of MLHL from lidar. The daily maximum MLHL characteristics of seasonal change in Beijing indicate that it is low in winter (1.404±0.751 km) and autumn (1.445±0.837 km) and high in spring (1.647±0.754 km) and summer (1.526±0.581 km). A significant phenomenon is found from 2014 to 2018: the magnitude of the diurnal cycle of MLHL increases year by year, with peak values of 1.291±0.646 km, 1.435±0.755 km, 1.577±0.739 km, 1.597±0.701 km and 1.629±0.751 km, respectively. It may partly benefit from the improvement of air quality. As to converting the column optical depth to surface pollution, the calculated PM2.5 using MLHL data from lidar shows better accuracy than that from radiosonde compared with observational PM2.5. Additionally, the accuracy of calculated PM2.5 using MLHL shows a diurnal cycle in the daytime, with the peak at 14:00 LST. The study provides a significant dataset of MLHL based on measurements and could be an effective reference for atmospheric models of surface air pollution calculation and analysis.

scholarly journals Influence of mixing layer height upon air pollution in urban and sub-urban areas

2006 ◽  
Vol 15 (6) ◽  
pp. 647-658 ◽  
Author(s):  
Klaus Schäfer ◽  
Stefan Emeis ◽  
Herbert Hoffmann ◽  
Carsten Jahn
Keyword(s):  
Air Pollution ◽  
Urban Areas ◽  
Mixing Layer ◽  
Layer Height ◽  
Mixing Layer Height

scholarly journals Impact of mixing layer height variations on air pollutant concentrations and health in a European urban area: Madrid (Spain), a case study

2020 ◽  
Vol 27 (33) ◽  
pp. 41702-41716 ◽  
Author(s):  
Pedro Salvador ◽  
Marco Pandolfi ◽  
Aurelio Tobías ◽  
Francisco Javier Gómez-Moreno ◽  
Francisco Molero ◽  
...  
Keyword(s):  
Urban Area ◽  
Mixing Layer ◽  
Air Pollutant ◽  
Layer Height ◽  
Pollutant Concentrations ◽  
Mixing Layer Height ◽  
Air Pollutant Concentrations

scholarly journals Observation and analysis of spatiotemporal characteristics of surface ozone and carbon monoxide at multiple sites in the Kathmandu Valley, Nepal

2018 ◽  
Vol 18 (19) ◽  
pp. 14113-14132 ◽  
Author(s):  
Khadak Singh Mahata ◽  
Maheswar Rupakheti ◽  
Arnico Kumar Panday ◽  
Piyush Bhardwaj ◽  
Manish Naja ◽  
...  
Keyword(s):  
Air Pollution ◽  
Mixing Layer ◽  
Mountain Pass ◽  
Kathmandu Valley ◽  
Emission Flux ◽  
Mixing Ratio ◽  
Top Down ◽  
Layer Height ◽  
Mixing Ratios ◽  
Mixing Layer Height

Abstract. Residents of the Kathmandu Valley experience severe particulate and gaseous air pollution throughout most of the year, even during much of the rainy season. The knowledge base for understanding the air pollution in the Kathmandu Valley was previously very limited but is improving rapidly due to several field measurement studies conducted in the last few years. Thus far, most analyses of observations in the Kathmandu Valley have been limited to short periods of time at single locations. This study extends the past studies by examining the spatial and temporal characteristics of two important gaseous air pollutants (CO and O3) based on simultaneous observations over a longer period at five locations within the valley and on its rim, including a supersite (at Bode in the valley center, 1345 m above sea level) and four satellite sites: Paknajol (1380 m a.s.l.) in the Kathmandu city center; Bhimdhunga (1522 m a.s.l.), a mountain pass on the valley's western rim; Nagarkot (1901 m a.s.l.), another mountain pass on the eastern rim; and Naikhandi (1233 m a.s.l.), near the valley's only river outlet. CO and O3 mixing ratios were monitored from January to July 2013, along with other gases and aerosol particles by instruments deployed at the Bode supersite during the international air pollution measurement campaign SusKat-ABC (Sustainable Atmosphere for the Kathmandu Valley – endorsed by the Atmospheric Brown Clouds program of UNEP). The monitoring of O3 at Bode, Paknajol and Nagarkot as well as the CO monitoring at Bode were extended until March 2014 to investigate their variability over a complete annual cycle. Higher CO mixing ratios were found at Bode than at the outskirt sites (Bhimdhunga, Naikhandi and Nagarkot), and all sites except Nagarkot showed distinct diurnal cycles of CO mixing ratio, with morning peaks and daytime lows. Seasonally, CO was higher during premonsoon (March–May) season and winter (December–February) season than during monsoon season (June–September) and postmonsoon (October–November) season. This is primarily due to the emissions from brick industries, which are only operational during this period (January–April), as well as increased domestic heating during winter, and regional forest fires and agro-residue burning during the premonsoon season. It was lower during the monsoon due to rainfall, which reduces open burning activities within the valley and in the surrounding regions and thus reduces sources of CO. The meteorology of the valley also played a key role in determining the CO mixing ratios. The wind is calm and easterly in the shallow mixing layer, with a mixing layer height (MLH) of about 250 m, during the night and early morning. The MLH slowly increases after sunrise and decreases in the afternoon. As a result, the westerly wind becomes active and reduces the mixing ratio during the daytime. Furthermore, there was evidence of an increase in the O3 mixing ratios in the Kathmandu Valley as a result of emissions in the Indo-Gangetic Plain (IGP) region, particularly from biomass burning including agro-residue burning. A top-down estimate of the CO emission flux was made by using the CO mixing ratio and mixing layer height measured at Bode. The estimated annual CO flux at Bode was 4.9 µg m−2 s−1, which is 2–14 times higher than that in widely used emission inventory databases (EDGAR HTAP, REAS and INTEX-B). This difference in CO flux between Bode and other emission databases likely arises from large uncertainties in both the top-down and bottom-up approaches to estimating the emission flux. The O3 mixing ratio was found to be highest during the premonsoon season at all sites, while the timing of the seasonal minimum varied across the sites. The daily maximum 8 h average O3 exceeded the WHO recommended guideline of 50 ppb on more days at the hilltop station of Nagarkot (159 out of 357 days) than at the urban valley bottom sites of Paknajol (132 out of 354 days) and Bode (102 out of 353 days), presumably due to the influence of free-tropospheric air at the high-altitude site (as also indicated by Putero et al., 2015, for the Paknajol site in the Kathmandu Valley) as well as to titration of O3 by fresh NOx emissions near the urban sites. More than 78 % of the exceedance days were during the premonsoon period at all sites. The high O3 mixing ratio observed during the premonsoon period  is of a concern for human health and ecosystems, including agroecosystems in the Kathmandu Valley and surrounding regions.

scholarly journals Mixing layer height and its implications for air pollution over Beijing, China

2016 ◽  
Vol 16 (4) ◽  
pp. 2459-2475 ◽  
Author(s):  
Guiqian Tang ◽  
Jinqiang Zhang ◽  
Xiaowan Zhu ◽  
Tao Song ◽  
Christoph Münkel ◽  
...  
Keyword(s):  
Air Pollution ◽  
Atmospheric Chemistry ◽  
Sensible Heat Flux ◽  
Mixing Layer ◽  
Meteorological Factor ◽  
Atmospheric Particles ◽  
Radiosonde Data ◽  
Sensible Heat ◽  
Layer Height ◽  
Mixing Layer Height

Abstract. The mixing layer is an important meteorological factor that affects air pollution. In this study, the atmospheric mixing layer height (MLH) was observed in Beijing from July 2009 to December 2012 using a ceilometer. By comparison with radiosonde data, we found that the ceilometer underestimates the MLH under conditions of neutral stratification caused by strong winds, whereas it overestimates the MLH when sand-dust is crossing. Using meteorological, PM2.5, and PM10 observational data, we screened the observed MLH automatically; the ceilometer observations were fairly consistent with the radiosondes, with a correlation coefficient greater than 0.9. Further analysis indicated that the MLH is low in autumn and winter and high in spring and summer in Beijing. There is a significant correlation between the sensible heat flux and MLH, and the diurnal cycle of the MLH in summer is also affected by the circulation of mountainous plain winds. Using visibility as an index to classify the degree of air pollution, we found that the variation in the sensible heat and buoyancy term in turbulent kinetic energy (TKE) is insignificant when visibility decreases from 10 to 5 km, but the reduction of shear term in TKE is near 70 %. When visibility decreases from 5 to 1 km, the variation of the shear term in TKE is insignificant, but the decrease in the sensible heat and buoyancy term in TKE is approximately 60 %. Although the correlation between the daily variation of the MLH and visibility is very poor, the correlation between them is significantly enhanced when the relative humidity increases beyond 80 %. This indicates that humidity-related physicochemical processes is the primary source of atmospheric particles under heavy pollution and that the dissipation of atmospheric particles mainly depends on the MLH. The presented results of the atmospheric mixing layer provide useful empirical information for improving meteorological and atmospheric chemistry models and the forecasting and warning of air pollution.

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