Aerosols influence the development of Atmospheric Boundary Layer (ABL) ensuing aggravated air pollution in megacities. ABL Height (ABLH) and Ventilation coefficient (VC) are key aspects in the pollution study that determines the vertical extent of dispersion of pollutants. To address the intricate, multi-sectoral problem of air pollution, a cogent and considerable approach of evalu-ating the influence of aerosol on ABLH is vital. The data from 2019 -2021 over Delhi, presents quantitative evaluation of radiation effect of aerosol on ABL. The study demonstrates qualita-tively that high aerosol loading lowers the ABLH, consecutively causes further increase in aerosol and PM2.5. Lowering of ABLH subsequently lowers the VC. The influence of aerosol on ABL and radiative forcing (RF) is critiqued with correlation coefficient (R) as-0.17 and -0.37 respec-tively. The cooling effect of the surface is enhanced as Aerosol Optical Depth (AOD) rises, further impeding the development of ABL. Further, through the interdependence between Single Scat-tering Albedo (SSA) and ABLH, it is speculated that the absorbing aerosols (AA) tend to increase the stability, ultimately leading to lower ABLH. Assessing the link between ABL and air pollution is vital not only for preventing and combating aerosol emissions in Delhi, but also for accurate air quality prediction and numerical weather prediction.

The present investigation outlines the crucial factors that influence the black carbon (BC) concentrations over a polluted metropolis, Kolkata (22.57 & DEG; N, 88.37 & DEG; E), India. Located in the eastern part of the Indo Gangetic Plain (IGP) outflow region and close to the land-ocean boundary, Kolkata is subject to contrasting seasonal maritime airflow from the Bay of Bengal and continental air mass from the IGP and Tibetan plateau region, which modulates the local concentration of BC. The origin of aerosol transport and associated atmospheric dynamics with high and low BC activities over Kolkata are examined during 2012-2015 using data from multi-technique sources which include measurements of ground-based instruments of aethalometer and multi-frequency microwave radiometer, reanalysis data from ERA-5 and MEERA-2, and model outputs from HYPSLIT back trajectory model simulations. The study highlights the control of IGP wind inflow on the occurrence of anomalous enhancements in BC concentration during weekends and holidays when local emissions are low. High BC events are associated with enhanced atmospheric heating below the boundary layer (2000 m) and significant negative surface radiative forcing. The response of the boundary layer to high and low BC episodes, shown in the diurnal variation in comparison with the seasonal mean, is investigated. Dominant suppression of morning and night-time boundary layer height is observed on high BC days. During the daytime in pre-monsoon, post-monsoon, and winter seasons, boundary layer height peaks are found to be strongly controlled by high BC episode occurrences as obtained from the hourly data of ERA-5.

The study examines the thermodynamic structure of the marine atmospheric boundary layer (MABL) and its effect on the aerosol dynamics in the Indian Ocean sector of Southern Ocean (ISSO) between 30 degrees S-67 degrees S and 57 degrees E-77 degrees E. It includes observations of aerosols and meteorology collected during the Xth Southern Ocean Expedition conducted in December 2017. The results revealed the effect of frontal-region-specific air-sea coupling on the thermodynamic structure of MABL and its role in regulating aerosols in ISSO. The MABL over the subtropical front was unstable and formed a well-evolved mixed layer ( 2400 m) capped by low-level inversions ( 660 m). Convective activities in the Sub-Antarctic Frontal region were associated with the Agulhas Retroflection Current, which supported the forma-tion of a well-developed mixed layer ( 1860 m). The mean estimates of aerosol optical depth (AOD) and black carbon (BC) mass concentrations were 0.095 +/- 0.006 and 50 +/- 14 ng m-3, respectively, and the resultant clear sky direct shortwave radiative forcing (DARF) and atmospheric heating rate (HR) were 1.32 +/- 0.11 W m-2 and 0.022 +/- 0.002 K day-1, respectively. In the polar front (PF) region, frequent mid-latitude cyclones led to highly stabilized MABL, supported low-level multi-layered clouds (>3-layers) and multiple high-level inversions (strength > 0.5 K m-1 > 3000 m). The clouds were mixed-phased with temperatures less than -12 degrees C at 3000 m altitude. Interestingly, there was higher loading of dust and BC aerosols (276 +/- 24 ng m-3), maximum AOD (0.109 +/- 0.009), clear sky DARF (1.73 +/- 0.02 W m-2), and HR (0.029 +/- 0.005 K day-1). This showed an accumulation of long-range advected anthro-pogenic aerosols within baroclinic-boundaries formed over the PF region. Specifically, in the region south of PF, weak convection caused weakly-unstable MABL with a single low-level inversion followed by no clouds/single-layer clouds. Predominant clean maritime air holding a small fraction of dust and BC accounted for lower estimates of AOD (0.071 +/- 0.004), BC concentrations (90 +/- 55 ng m-3) and associated clear sky DARF and HR were 1.16 +/- 0.06 W m-2 and 0.019 +/- 0.001 K day-1, respectively.

Using a single column model with ground-based, aircraft, and satellite data sets we assess the combined role of smoke and dust aerosols, land degradation/aridization (LDA), and their impact on the planetary boundary layer (PBL) in influencing near-surface air temperature over the Sahel. Our study is unique because it assesses the combined role of smoke and dust aerosols on PBL evolution and near-surface air temperatures during both day and nighttime. More importantly, using a theoretical framework, we provide a careful explanation of the geophysical processes responsible for the changes in PBL and near-surface air temperature. Our results indicate that during northern hemisphere winter months, dust, and smoke over Sahel radiatively combine to impact the PBL. We show that aerosol mixtures dominated by dust modify PBL height in a manner that minimizes/maximizes surface layer cooling/warming at times when daytime maximum/nocturnal minimum temperatures occur. Furthermore, we find that increasing smoke contribution to total column aerosol optical extinction counteracts nighttime warming through daytime cooling. When smoke constitutes half or more of to the total column aerosol optical extinction, the ratio of longwave to shortwave radiative forcing is less than 10%, and nighttime cooling ensues. Minimum temperature is most sensitive to changes in mid-visible aerosol optical depth (AOD) values <1 and doubling of dust AOD within this range during the 1950-1980 Sahelian LDA event is estimated to have a nocturnal warming potential of 0.6 degrees C.

Aerosols with different vertical distribution and various optical properties induce diverse heating rates and thereby affecting convective boundary layer (CBL) development. Our results showed consistent CBL-suppression of aerosols during daytime with numerical experiments, in which aerosols were specified at different heights with synthesized single scattering albedo from 64 studies and asymmetry factor from 20 studies globally. Absorbing aerosols concentrated below but close to the CBL top had the strongest suppression effect on CBL development relative to that concentrated near surface or above CBL. Aerosol cooling effect by attenuating incident solar radiation and surface heat flux exceeded its warming effect by reheating the atmosphere layer with absorbed shortwave radiation, and eventually declined net heating rate, which inhibited CBL development, lowered mixed-layer potential temperature and stabilized atmospheric stratification. Stove effect of absorbing aerosols (CBL enhancement) under a zero background aerosol extinction coefficient is negligible for dominant dome effect (CBL suppression) which consistently suppresses CBL development regardless of aerosol vertical height and background aerosol extinction coefficient. Our study also highlighted the importance of specifying background aerosol extinction coefficient in numerical experiments for accurate assessment of aerosol radiative forcing and CBL-aerosol interactions.

This work is motivated by the identification of the land-atmosphere interactions as one of the key sources of uncertainty in climate change simulations. It documents new developments in related processes, namely, boundary layer/convection/clouds parameterizations and land surface parameterization in the Earth System Model of the Institut Pierre Simon Laplace (IPSL). Simulations forced by prescribed oceanic conditions are produced with different combinations of atmospheric and land surface parameterizations. They are used to explore the sensitivity to the atmospheric physics and/or soil physics of major biases in the near surface variables over continents, the energy and moisture coupling established at the soil/atmosphere interface in not too wet (energy limited) and not too dry (moisture limited) soil moisture regions also known as transition or hot-spot regions, the river runoff at the outlet of major rivers. The package implemented in the IPSL-Climate Model for the Phase 6 of the Coupled Models Intercomparison Project (CMIP6) allows us to reduce several biases in the surface albedo, the snow cover, and the continental surface air temperature in summer as well as in the temperature profile in the surface layer of the polar regions. The interactions between soil moisture and atmosphere in hotspot regions are in better agreement with the observations. Rainfall is also significantly improved in volume and seasonality in several major river basins leading to an overall improvement in river discharge. However, the lack of consideration of floodplains and human influences in the model, for example, dams and irrigation, impacts the realism of simulated discharge.

The atmospheric boundary layer (ABL) is one of the most fundamental yet complex components of the Earth's atmosphere. Hence, studying the ABL has important theoretical value and practical significance. In this paper, the structural characteristics and heating (cooling) rate of the ABL in summer over the Northern Tibetan Plateau (NTP) were analysed using radiosonde observation data from the Amdo and Nagqu regions. The results indicate that the summertime ABL height over the NTP exhibited obvious diurnal variations, with the ABL height during the dry season being greater than that during the rainy season. The maximum convective boundary layer (CBL) height during the daytime reached 3200 m and 2500 m in the dry and rainy seasons, respectively, and the mean maximum CBL height was approximately 2500 m; the maximum stable boundary layer (SBL) height at night reached 900 m, and the mean maximum SBL height was approximately 500 m. The wind speed dominated by westerly wind in the dry season was greater than that dominated by easterly wind in the rainy season, and the zonal (meridional) wind speed (shear) on sunny days was greater than that on cloudy days. The inverse humidity phenomenon occurred in both Amdo and Nagqu, and the strong humidity inversion occurred mainly at midnight on sunny days and at noon on cloudy days. The heating (cooling) rate of the ABL displayed obvious diurnal variations, with the rates being greater on sunny days and lower on cloudy and rainy days. Furthermore, the mean values of the daytime heating rate and nighttime cooling rate of the ABL were relatively equal, indicating that the atmospheric energy budget was, for the most part, balanced.

Atmospheric aerosols have been found to influence the development of planetary boundary layer (PBL) and hence to aggravate haze pollution in megacities. PBL height (PBLH) determines the vertical extent to which the most pollutant effectively disperses and is a key argument in pollution study. In this study, we quantitatively evaluate aerosol radiation effect on PBL, as well as assessment of surface cooling effect and atmosphere heating effect. All the data are measured at a site of Beijing from 2014 to 2017, of which PBLH is retrieved from micro pulse lidar and aerosol optical depth (AOD) from sunphotometer. Case study shows qualitatively that relative high aerosol load reduces PBLH, and in turn causes a high surface PM2.5 concentration. We preliminarily reveal the influential mechanism of aerosol on PBL. The influence of aerosol on the radiation flux of PBL is analyzed, with the correlation coefficient (R) of 0.938 between AOD and radiative forcing of BOA (RFBOA) and R = 0.43 between RFBOA and PBLH. Also, AOD is found to negatively correlate with PBLH (R = -0.41). With the increase of AOD, the cooling effect of surface is enhanced, and further impede the development of PBL. Due to aerosol-induced reduction of PBLH, near surface PM2.5 concentration surges and presents an exponential growth following AOD. Then, it is speculated and testified that the relationship between SSA (single scatting albedo) and PBLH would be determined by the location of absorbing aerosol within PBL. The upper PBL absorbing aerosol may decrease PBLH, while the lower absorbing aerosol appear to enhance PBLH. The study probably can provide effective observational evidence for understanding the effect of aerosol on PBL and be a reference of air pollution mitigation in Beijing and its surrounding areas. (C) 2019 Elsevier Ltd. All rights reserved.

The aerosol microphysical, optical and radiative properties of the whole column and upper planetary boundary layer (PBL) were investigated during 2013 to 2018 based on long-term sun-photometer observations at a surface site (similar to 106 m a.s.l.) and a mountainous site (similar to 1225 m a.s.l.) in Beijing. Raman-Mie lidar data combined with radiosonde data were used to explore the aerosol radiative effects to PBL during dust and haze episodes. The results showed size distribution exhibited mostly bimodal pattern for the whole column and the upper PBL throughout the year, except in July for the upper PBL, when a trimodal distribution occurred due to the coagulation and hygroscopic growth of fine particles. The seasonal mean values of aerosol optical depth at 440 nm for the upper PBL were 0.31 +/- 0.34, 0.30 +/- 0.37, 0.17 +/- 0.30 and 0.14 +/- 0.09 in spring, summer, autumn and winter, respectively. The single-scattering albedo at 440 nm of the upper PBL varied oppositely to that of the whole column, with the monthly mean value between 0.91 and 0.96, indicating weakly to slightly strong absorptive ability at visible spectrum. The monthly mean direct aerosol radiative forcing at the Earth's surface and the top of the atmosphere varied from -40 +/- 7 to -105 +/- 25 and from -18 +/- 4 to -49 +/- 17 W m(-2), respectively, and the maximum atmospheric heating was found in summer (similar to 66 +/- 12 W m(-2)). From a radiative point of view, during dust episode, the presence of mineral dust heated the lower atmosphere, thus promoting vertical turbulence, causing more air pollutants being transported to the upper air by the increasing PBLH. In contrast, during haze episode, a large quantity of absorbing aerosols (such as black carbon) had a cooling effect on the surface and a heating effect on the upper atmosphere, which favored the stabilization of PBL and occurrence of inversion layer, contributing to the depression of the PBLH. (C) 2019 Elsevier B.V. All rights reserved.

A qualitative assessment on the effect of boundary layer dynamics in the estimation of clear sky black carbon (BC) radiative forcing has been made considering the debate on the lower bound and possible uncertainties in the aerosol radiative forcing estimation. Comprehensive measurements made on aerosol optical and physical properties, near surface BC mass concentrations and Lidar derived aerosol back scatter intensity profiles at three selected locations in India (Visakhapatnam, Kharagpur, and Kolkata) are utilized for this purpose. Sensitivity analysis carried out to estimate the errors in short wave (SW) BC forcing computation indicated that nonincorporation of diurnal changes in the boundary layer depth into the models may lead to over estimation of diurnally averaged (as the study is limited to short wave radiative forcing, diurnally averaged forcing refers to day-time averaged) BC forcing. The relative errors may vary between 7 to 70% depending on the season and the location changes in boundary layer depth day-time behaviour. The results reported in the present study, though specific to the study locations, clearly indicate that a more systematic approach is needed to investigate the sensitivity of aerosol radiative forcing to various atmospheric parameters and processes within the boundary layer, particularly at stations characterised by strong anthropogenic influence and large diurnal temperature variability that affect the boundary layer depth.