Search

The planetary boundary layer height is a very important parameter in the atmosphere because it determines the range where the most effective dispersion processes take place, and it serves as a medium for the vertical transport of heat, moisture, and pollutants. The accurate estimation of boundary layer height (BLH) is vital for air pollution prediction. In this paper, the BLH estimated by AD-Net was compared with that from the ECMWFs over East Asia from September 2015 to August 2018. A continuous 24 h BLH estimation from AD-Net generally matched with the aerosol vertical structures. Diurnal and seasonal variation and spatial variation of BLH can also be shown, suggesting the good performance of AD-Net BLH. The comparison of seasonal mean BLH between AD-Net and ECMWFs was conducted at 20 lidar sites. On average, there was an underestimation of the ECMWFs, mostly in summer and winter. A significant disagreement between AD-Net and the ECMWFs was noted, especially over coastal areas and mountain areas. In order to investigate the difference between them, two BLHs were compared under different land cover types and climate conditions. In general, the BLH of the ECMWFs was less than that of AD-Net over most of the land cover types in summer and winter. The smallest differences (0.26 km) existed over water surfaces in winter compared with AD-Net, and the largest underestimation (1.42 km) occurred over grassland surfaces in summer. Similarly, all the BLHs of the ECMWFs were lesser than those of AD-Net under different climatological conditions in summer and winter. The mean difference between AD-Net BLH and ECMWFs BLH was 1.05, 0.71, and 0.48 km for arid regions, semi-arid and semi-wet regions, and wet regions, respectively. The largest underestimation occurred over arid regions in winter, with a value of 1.42 km. The smallest underestimation occurred over wet regions, with a value of 0.27 km. The present research provides better insight into the BLH performance in the ECMWFs reanalysis data. The new continuous PBL dataset can be used to improve the model parameterization of PBL and our understanding of the atmospheric transport of pollutants which affect air quality and human health.

Publisher Copyright: © Copyright © 2021 Huo, Wang, Paasonen, Liu, Tang, Ma, Petaja, Kerminen and Kulmala. Boundary layer height (BLH) is an important parameter in climatology and air pollution research, especially in urban city. We calculated the BLH with a bulk Richardson number (Ri) method over urban cities of China during 1980–2018 using European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-interim data after carefully validation with sounding data obtained from two meteorology stations in eastern China during 2010–2018. The values of BLH between these two types of data have correlation coefficients in the range of 0.65–0.87, which indicates that it is reasonable to analyze long-term trends of the BLH from ERA data sets. Using ERA-interim calculated BLH, we found that there is an increasing trend in the daytime BLH in most cities of eastern China, particularly during the spring season. A correlation analysis between the BLH and temperature, wind speed, relative humidity and visibility revealed that the variability in meteorological parameters, as well as in aerosol concentrations over highly polluted eastern China, play important roles in the development of the BLH.

Thai Environmental Engineering Journal (TEEJ), 35, 3, 1-11

This paper describes diurnal and seasonal variations of trace air pollutants include surface ozone (O3), oxides of nitrogen (NOx), carbon monoxide (CO), volatile organic compounds (Benzene, Toluene, Ethyl Benzene, Xylenes which are classified as BTEX)), ammonia (NH3), sulphur dioxide (SO2), and meteorological parameters observed at Kannur town (11.87° N, 75.37° E, 2 m msl) for a period of one year from September 2019. Seasonal variations of trace air pollutants exhibit a daytime maximum during winter due to the enhanced local emission and long-range transport, and minimum during the monsoon period. Surprisingly, air pollutants except O3 show a reduction in concentration in the months of April 2020 due to countrywide lockdown in the wake of restricting the spread of COVID 19. Weekday/weekend variations of air pollutants reveal that high concentrations of O3 are found on weekends compared to weekdays, unlike the concentrations of all other pollutants are found low during weekends. From the analysis of the chemical coupling between NO, NO2, NOx, O3, and OX (=O3+NO2), it is found that OX has both regional and local contributions on NOx. Intercorrelations between trace pollutants showed a strong positive correlation between O3 and CO, a negative correlation between O3 and NOx.

The top of the boundary layer, referred to as the planetary boundary layer height (BLH), is an important physical parameter in atmospheric numerical models, which has a critical role in atmospheric simulation, air pollution prevention, and climate prediction. The traditional methods for determining BLHs using Doppler lidar vertical velocity variance (σw2) can be classified into the variance and peak methods, which depend on atmospheric conditions due to their use of a single threshold, hence limiting their ability to estimate diurnal BLHs. Edge detection (ED) was later introduced in BLH estimation due to its ability to identify the 2D gradient of an image. A key step in ED is automatically identifying the edge of BLHs based on the peaks of the profile, hence avoiding the influence of extreme atmospheric conditions. Two cases in the diurnal cycle on 4 March 2019 and 8 July 2019 reveal that ED outperforms both the variance and peak methods in nighttime and extreme atmospheric conditions. The retrieved BLHs from 2018 to 2020 were compared with radiosonde (RS) measurements for the same time at the neutral, stable, and convective boundary layers. The correlation coefficient (R: 0.4 vs. 0.05, 0.14, 0.26 vs. −0.10, −0.16, 0.35 vs. 0.01, 0.16) and root mean square error (RMSE (km): 0.58 vs. 0.82, 0.90, 0.37 vs. 1.01, 0.50, 0.66 vs. 0.98, 0.82) obtained by the ED method were higher and lower than those obtained by the variance and peak methods, respectively. The mean absolute error (MAE) of the ED method under the NBL, SBL, and CBL conditions are lower than the variance and peak methods (MAE (km): 0.44, 0.14, 0.50 vs. 0.62, 0.34, 0.64, 0.59, 0.75, 0.74), respectively. The mean relative error (MRE) of the ED method is lower than the variance and peak methods under the NBL condition (MRE: −8.88% vs. −18.39%, 13.91%). Under the SBL, the MRE of the ED method is lower than the variance method and higher than the peak method (−38.64%, vs. −152.23%, 14.02%). Under the CBL, the MRE of the ED method is lower than the variance method and higher than the peak method (−15.07% vs. 2.24%, 5.64%). In addition, the comparison between ED and wavelet covariance transform (WCT) method and RS measurements showed that the ED method has a similar performance with the WCT method and is even better. In the long-term analysis, the hourly and monthly BLHs in the diurnal and annual cycles, respectively, as obtained by ED, were highly consistent with the RS measurements and obtained the lowest standard error. In the annual cycle, the retrieved BLHs in summer and autumn were higher than those retrieved in spring and winter.

The planetary boundary layer height (PBLH) is the atmospheric region closest to the earth&rsquo, s surface and has important implications on weather forecasting, air quality, and climate research. However, lidar-based methods traditionally used to determine PBLH&mdash, such as the ideal profile fitting method (IPF), maximum gradient method, and wavelet covariance transform&mdash, are not only heavily influenced by cloud layers, but also rely heavily on a low signal-to-noise ratio (SNR). Therefore, a random sample fitting (RANSAF) method was proposed for PBLH detection based on combining the random sampling consensus and IPF methods. According to radiosonde measurements, the testing of simulated and satellite-based signals shows that the proposed RANSAF method can reduce the effects of the cloud layer and significantly fluctuating noise on lidar-based PBLH detection better than traditional algorithms. The low PBLH bias derived by the RANSAF method indicates that the improved algorithm has a superior performance in measuring PBLH under a low SNR or when a cloud layer exists where the traditional methods are mostly ineffective. The RANSAF method has the potential to determine regional PBLH on the basis of satellite-based lidar backscatter profiles.

The diurnal evolution of the atmospheric boundary layer—the lowermost part of the atmosphere where the majority of human activity and meteorological phenomena take place—is described by its depth. Additionally, the boundary layer height (BLH) and the turbulence intensity strongly impact the pollutant diffusion, especially during transition periods. Based on integrated observations from a 325-m meteorological tower and a Doppler Wind lidar in the center of Beijing, the entire diurnal cycle of urban BLH in December 2016 was characterized. Results highlight that the Doppler lidar exhibited it is well suited for monitoring convective BLH while it trudges in monitoring stable BLH, while a 325-m meteorological tower provided an important supplement for Doppler lidar under nocturnal boundary layer and heavily polluted conditions. For the diurnal cycle, under light wind condition, the pattern of urban BLH was largely modulated by thermal forcing of solar radiation and may partly be affected by wind speed. While under strong wind condition, the pattern of urban BLH was largely modulated both by thermal forcing and dynamical forcing. The present work also presented evidence for several new features in the morning and afternoon transitions of the urban boundary layer, showing the duration of the morning transition varied between 1 and 5 h, with the largest value occurring under weak wind with high PM2.5 concentration; while the afternoon transition ranged from 3 to 6 h, which was positively (negatively) correlated to wind speed (PM2.5 concentration). Our work highlights that weak wind speed (weak dynamic motion) and heavy aerosol pollution (weak thermal forcing due to the effect of cooling) can dramatically affect the evolution of the boundary layer.

Understanding the behavior of the planetary boundary layer is fundamental to better comp rehend some phenomena such as the dispersion of pollutants in urban areas. Th is study aims at estimating the characteristic parameters and the spectral properties of the atmospheric turbulence on the surface boundary layer, especially the height of the at mospheric boundary layer in the south of Rio Grande do Su l state, in Brazil, based on data collected by micro meteorological instruments placed close to the surface. The characteristic parameters and the spectral propert ies were analy zed in the light of Monin-Obukhov's similarity theory in different stability conditions. The boundary layer height was determined by using the turbulent spectra of the zonal wind velocity whose data was collected fro m August 28th to November 11th, 2006, on a tower located 20 km south of Rio Grande. Results of the turbulence kinetic energy, the friction velocity and Obukhov's length are in agreement with the findings of other studies carried out in the region. After making adjustments regarding the atmospheric stability, the roughness length properly represented the characteristics of the landscape in the region where the data collection tower was placed. The spectral analysis showed that Monin and Obukhov's similarity theory is not appropriate to describe the spectral characteristics of the turbulence in the somewhat unstable conditions in the region. Mean values of 1168.87 m and 291.90 m were obtained for the heights of the convective and the nocturnal boundary layers, respectively. The methodology that was used to estimate the boundary layer height was satisfactory to represent both its diurnal and its nocturnal evolution.

The statistical properties of five boundary layer height definitions were examined in 6,593 NCAR GPS dropsonde observations of the hurricane environment. Based on similar composite analysis studies, these boundary layer height estimates were divided into two categories based on their analytical characteristics. Three dynamical methods of estimating the boundary layer height were combined with two thermodynamical methods of estimating the mixed layer depth to numerically interrogate the physical properties of hurricanes within two primary modes of variability: azimuthal and geographic region. The results confirmed the vertical bifurcation of dynamical and thermodynamical height estimates and indicated a consistent distinction in the radial variability of each class. Moreover, the tangential wind field was well-described by the modified Rankine vortex. A characteristic decrease in boundary layer height with decreasing radius to the storm center was expressed in four of the five definitions. The non-uniform azimuthal distribution of relative radial winds and ill-behaved inflow layer depths precluded meaningful comparisons of boundary layer height in the rear storm-relative semicircle. While boundary layer height estimates failed to exhibit any significant regional variability, the right-front storm-relative quadrant appeared to exhibit non-trivial increases in mean boundary layer height. http://archive.org/details/variabilityinhur1094542751 Lieutenant, United States Navy Approved for public release; distribution is unlimited.

Ozone (O3) is a secondary pollutant dependent on complex photochemical reactions of nitrogen oxides (NOx) and volatile organic compounds (VOCs) and is sensitive to meteorological conditions that govern solar radiation, temperature, and wind speed/direction (Stockwell, 2011). The U.S. Environmental Protection Agency (USEPA) has classified O3 as one of the six criteria pollutants that is considered harmful to both plants and human health (Hollingsworth, 2007). The current study investigates the influence of the diurnal cycle of the BL on the surface air pollutants. Specifically, it examines how the nighttime and transition period turbulence impacts the concentration of ozone at the surface and in the atmospheric column during the following day. In order to complete the study, a series of models including the Weather Research and Forecasting (WRF) model and the Comprehensive Air Quality model with Extensions (CAMx) are used to simulate atmospheric conditions in the Maryland and Texas areas. BL processes such as the minimum diffusivity or BL parameterization within CAMx are investigated. The Blackadar scheme was found to artificially suppress the nocturnal BL height and appears to be the cause of a 15 ppbv high model bias. An experiment is then conducted where a minimum BL height of 160 m and an improvement of 7% in the median model bias are found in the Maryland area. With Maryland being in a NOx-limited regime, the same process of setting a minimum height is tested in the Texas area using the YSU scheme but minimal differences produced minuscule changes in the vertical diffusivity. The use of the Ri number improved the model bias by another 5 ppbv or 13% over using the Blackadar BL scheme. A new algorithm to predict the nocturnal BL depth is implemented into the WRF YSU scheme, which scales the Ribc with the Obukhov length adding a dependency on near surface properties of the flow. The algorithm is tested using meteorological surface measurements and tower measurements, along with pollutant measurements in the Texas and Maryland areas. The median model bias improved by 10% compared to using a static critical bulk Ri number.

In the present study, ventilation coefficient (VC) was estimated in order to understand the concentration of pollutants over the urban region of Hyderabad during 2009–2011. Nocturnal boundary layer height (BLH) was calculated using the accurate (0.2% for Refractivity Profiles) high vertical resolution global positioning system radio occultation (GPSRO), Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC)-derived one-dimensional variational (1-DVAR) refractivity profiles, and observations of boundary layer LIDAR (BLL). The statistical results revealed that the coefficient of determination (R2) between LIDAR- and GPSRO-estimated BLH is 0.51, whereas that for VC is 0.68. The maximum BLH observed during the study period was maximum in the summer season and the minimum was observed in monsoon season, whereas the maximum VC was observed during summer and the minimum in winter. When the BLH and VC are low, the pollutant concentration of black carbon (BC) is higher and vice versa. This means that the dispersion of pollutants in the lower atmosphere is due to convective mixing. It was found that high VC values could dilute air pollutants whereas low values leads to more pollution.

With the green economy being promoted as a path to sustainable development and food security within the African continent, the influx of agricultural land is proliferating at a rapid pace often replacing natural savannah forests. Where agriculture is primarily rainfed, the possible adverse impacts of agricultural land influx on rainfall occurrences in water-limited areas such as West Africa warrant attention. Using field observations complemented by model calculations in southeastern Burkina Faso, the main causes of a 10-30% suppressed daytime rainfall recorded over agricultural fields when referenced to natural savannah forests are examined. Measurements and model runs reveal that the crossing of the mixed layer height and lifting condensation levels, a necessary condition for cloud formation and subsequent rainfall occurrence, was 30% more frequent above the natural savannah forest. This increase in crossing statistics was primarily explained by increases in measured sensible heat flux above the savannah forest rather than differences in lifting condensation heights.