scholarly journals On factors controlling marine boundary layer aerosol optical depth

2014 ◽  
Vol 119 (6) ◽  
pp. 3321-3334 ◽  
Author(s):  
Tao Luo ◽  
Renmin Yuan ◽  
Zhien Wang
Keyword(s):  
Boundary Layer ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Marine Boundary Layer

scholarly journals Saharan dust contribution to the Caribbean summertime boundary layer – a lidar study during SALTRACE

2016 ◽  
Vol 16 (18) ◽  
pp. 11535-11546 ◽  
Author(s):  
Silke Groß ◽  
Josef Gasteiger ◽  
Volker Freudenthaler ◽  
Thomas Müller ◽  
Daniel Sauer ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Marine Boundary Layer ◽  
Volume Fraction ◽  
Saharan Dust ◽  
Depolarization Ratio ◽  
Mean Values ◽  
Lidar Ratio ◽  
Linear Depolarization Ratio

Abstract. Dual-wavelength lidar measurements with the small lidar system POLIS of the Ludwig-Maximilians-Universität München were performed during the SALTRACE experiment at Barbados in June and July 2013. Based on high-accuracy measurements of the linear depolarization ratio down to about 200 m above ground level, the dust volume fraction and the dust mass concentration within the convective marine boundary layer can be derived. Additional information from radiosonde launches at the ground-based measurement site provide independent information on the convective marine boundary layer height and the meteorological situation within the convective marine boundary layer. We investigate the lidar-derived optical properties, the lidar ratio and the particle linear depolarization ratio at 355 and 532 nm and find mean values of 0.04 (SD 0.03) and 0.05 (SD 0.04) at 355 and 532 nm, respectively, for the particle linear depolarization ratio, and (26 ± 5) sr for the lidar ratio at 355 and 532 nm. For the concentration of dust in the convective marine boundary layer we find that most values were between 20 and 50 µgm−3. On most days the dust contribution to total aerosol volume was about 30–40 %. Comparing the dust contribution to the column-integrated sun-photometer measurements we see a correlation between high dust contribution, high total aerosol optical depth and a low Angström exponent, and of low dust contribution with low total aerosol optical depth.

scholarly journals How much of the global aerosol optical depth is found in the boundary layer and free troposphere?

2017 ◽  
Author(s):  
Quentin Bourgeois ◽  
Annica M. L. Ekman ◽  
Jean-Baptiste Renard ◽  
Radovan Krejci ◽  
Abhay Devasthale ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Climate Models ◽  
Convective Transport ◽  
Free Troposphere ◽  
Range Transport ◽  
Aerosol Classification ◽  
The Tropics ◽  
The Vertical Distribution

Abstract. The global aerosol extinction from the CALIOP space lidar was used to compute aerosol optical depth (AOD) over a nine-year period (2007–2015) and partitioned between the boundary layer (BL) and the free troposphere (FT) using BL heights obtained from the ERA-Interim archive. The results show that the vertical distribution of AOD does not follow the diurnal cycle of the BL but remains similar between day and night highlighting the presence of a residual layer during night. The BL and FT contribute 69 % and 31 %, respectively, to the global tropospheric AOD during daytime in line with observations obtained using the Light Optical Aerosol Counter (LOAC) instrument. The FT AOD contribution is larger in the tropics than at mid-latitudes which indicates that convective transport largely controls the vertical profile of aerosols. Over oceans, the FT AOD contribution is mainly governed by long-range transport of aerosols from emission sources located within neighboring continents. According to the CALIOP aerosol classification, dust and smoke particles are the main aerosol types transported into the FT. Overall, the study shows that the fraction of AOD in the FT – and thus potentially located above low-level clouds – is substantial and deserves more attention when evaluating the radiative effect of aerosols in climate models. More generally, the results have implications for process determining the overall budgets, sources, sinks and transport of aerosol particles and their description in atmospheric models.

scholarly journals Modeling regional aerosol variability over California and its sensitivity to emissions and long-range transport during the 2010 CalNex and CARES campaigns

2014 ◽  
Vol 14 (6) ◽  
pp. 7187-7303 ◽  
Author(s):  
J. D. Fast ◽  
J. Allan ◽  
R. Bahreini ◽  
J. Craven ◽  
L. Emmons ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Aerosol Optical Depth ◽  
Long Range ◽  
Optical Depth ◽  
Trace Gases ◽  
Organic Aerosol ◽  
Global Model ◽  
Long Range Transport ◽  
Anthropogenic Emissions ◽  
Range Transport

Abstract. The performance of the Weather Research and Forecasting regional model with chemistry (WRF-Chem) in simulating the spatial and temporal variations in aerosol mass, composition, and size over California is quantified using measurements collected during the California Nexus of Air Quality and Climate Experiment (CalNex) and the Carbonaceous Aerosol and Radiative Effects Study (CARES) conducted during May and June of 2010. The extensive meteorological, trace gas, and aerosol measurements collected at surface sites and along aircraft and ship transects during CalNex and CARES were combined with operational monitoring network measurements to create a single dataset that was used to evaluate the one configuration of the model. Simulations were performed that examined the sensitivity of regional variations in aerosol concentrations to anthropogenic emissions and to long-range transport of aerosols into the domain obtained from a global model. The configuration of WRF-Chem used in this study is shown to reproduce the overall synoptic conditions, thermally-driven circulations, and boundary layer structure observed in region that controls the transport and mixing of trace gases and aerosols. However, sub-grid scale variability in the meteorology and emissions as well as uncertainties in the treatment of secondary organic aerosol chemistry likely contribute to errors at a primary surface sampling site located at the edge of the Los Angeles basin. Differences among the sensitivity simulations demonstrate that the aerosol layers over the central valley detected by lidar measurements likely resulted from lofting and recirculation of local anthropogenic emissions along the Sierra Nevada. Reducing the default emissions inventory by 50% led to an overall improvement in many simulated trace gases and black carbon aerosol at most sites and along most aircraft flight paths; however, simulated organic aerosol was closer to observed when there were no adjustments to the primary organic aerosol emissions. The model performance for some aerosol species was not uniform over the region, and we found that sulfate was better simulated over northern California whereas nitrate was better simulated over southern California. While the overall spatial and temporal variability of aerosols and their precursors were simulated reasonably well, we show cases where the local transport of some aerosol plumes were either too slow or too fast, which adversely affects the statistics regarding the differences between observed and simulated quantities. Comparisons with lidar and in-situ measurements indicate that long-range transport of aerosols from the global model was likely too high in the free troposphere even though their concentrations were relatively low. This bias led to an over-prediction in aerosol optical depth by as much as a factor of two that offset the under-predictions of boundary-layer extinction resulting primarily from local emissions. Lowering the boundary conditions of aerosol concentrations by 50% greatly reduced the bias in simulated aerosol optical depth for all regions of California. This study shows that quantifying regional-scale variations in aerosol radiative forcing and determining the relative role of emissions from local and distant sources is challenging during "clean" conditions and that a wide array of measurements are needed to ensure model predictions are correct for the right reasons. In this regard, the combined CalNex and CARES datasets are an ideal testbed that can be used to evaluate aerosol models in great detail and develop improved treatments for aerosol processes.

scholarly journals How much of the global aerosol optical depth is found in the boundary layer and free troposphere?

2018 ◽  
Vol 18 (10) ◽  
pp. 7709-7720 ◽  
Author(s):  
Quentin Bourgeois ◽  
Annica M. L. Ekman ◽  
Jean-Baptiste Renard ◽  
Radovan Krejci ◽  
Abhay Devasthale ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Climate Models ◽  
Convective Transport ◽  
Free Troposphere ◽  
Range Transport ◽  
Aerosol Classification ◽  
The Tropics ◽  
The Vertical Distribution

Abstract. The global aerosol extinction from the CALIOP space lidar was used to compute aerosol optical depth (AOD) over a 9-year period (2007–2015) and partitioned between the boundary layer (BL) and the free troposphere (FT) using BL heights obtained from the ERA-Interim archive. The results show that the vertical distribution of AOD does not follow the diurnal cycle of the BL but remains similar between day and night highlighting the presence of a residual layer during night. The BL and FT contribute 69 and 31 %, respectively, to the global tropospheric AOD during daytime in line with observations obtained in Aire sur l'Adour (France) using the Light Optical Aerosol Counter (LOAC) instrument. The FT AOD contribution is larger in the tropics than at mid-latitudes which indicates that convective transport largely controls the vertical profile of aerosols. Over oceans, the FT AOD contribution is mainly governed by long-range transport of aerosols from emission sources located within neighboring continents. According to the CALIOP aerosol classification, dust and smoke particles are the main aerosol types transported into the FT. Overall, the study shows that the fraction of AOD in the FT – and thus potentially located above low-level clouds – is substantial and deserves more attention when evaluating the radiative effect of aerosols in climate models. More generally, the results have implications for processes determining the overall budgets, sources, sinks and transport of aerosol particles and their description in atmospheric models.

scholarly journals Modeling regional aerosol and aerosol precursor variability over California and its sensitivity to emissions and long-range transport during the 2010 CalNex and CARES campaigns

2014 ◽  
Vol 14 (18) ◽  
pp. 10013-10060 ◽  
Author(s):  
J. D. Fast ◽  
J. Allan ◽  
R. Bahreini ◽  
J. Craven ◽  
L. Emmons ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Air Quality ◽  
Aerosol Optical Depth ◽  
Long Range ◽  
Optical Depth ◽  
Trace Gases ◽  
Organic Aerosol ◽  
Long Range Transport ◽  
Range Transport ◽  
Aerosol Radiative

Abstract. The performance of the Weather Research and Forecasting regional model with chemistry (WRF-Chem) in simulating the spatial and temporal variations in aerosol mass, composition, and size over California is quantified using the extensive meteorological, trace gas, and aerosol measurements collected during the California Nexus of Air Quality and Climate Experiment (CalNex) and the Carbonaceous Aerosol and Radiative Effects Study (CARES) conducted during May and June of 2010. The overall objective of the field campaigns was to obtain data needed to better understand processes that affect both climate and air quality, including emission assessments, transport and chemical aging of aerosols, aerosol radiative effects. Simulations were performed that examined the sensitivity of aerosol concentrations to anthropogenic emissions and to long-range transport of aerosols into the domain obtained from a global model. The configuration of WRF-Chem used in this study is shown to reproduce the overall synoptic conditions, thermally driven circulations, and boundary layer structure observed in region that controls the transport and mixing of trace gases and aerosols. Reducing the default emissions inventory by 50% led to an overall improvement in many simulated trace gases and black carbon aerosol at most sites and along most aircraft flight paths; however, simulated organic aerosol was closer to observed when there were no adjustments to the primary organic aerosol emissions. We found that sulfate was better simulated over northern California whereas nitrate was better simulated over southern California. While the overall spatial and temporal variability of aerosols and their precursors were simulated reasonably well, we show cases where the local transport of some aerosol plumes were either too slow or too fast, which adversely affects the statistics quantifying the differences between observed and simulated quantities. Comparisons with lidar and in situ measurements indicate that long-range transport of aerosols from the global model was likely too high in the free troposphere even though their concentrations were relatively low. This bias led to an over-prediction in aerosol optical depth by as much as a factor of 2 that offset the under-predictions of boundary-layer extinction resulting primarily from local emissions. Lowering the boundary conditions of aerosol concentrations by 50% greatly reduced the bias in simulated aerosol optical depth for all regions of California. This study shows that quantifying regional-scale variations in aerosol radiative forcing and determining the relative role of emissions from local and distant sources is challenging during `clean' conditions and that a wide array of measurements are needed to ensure model predictions are correct for the right reasons. In this regard, the combined CalNex and CARES data sets are an ideal test bed that can be used to evaluate aerosol models in great detail and develop improved treatments for aerosol processes.

scholarly journals Climatological aspects of aerosol optical properties in Northern Greece

2003 ◽  
Vol 3 (2) ◽  
pp. 2059-2099 ◽  
Author(s):  
E. Gerasopoulos ◽  
M. O. Andreae ◽  
C. S. Zerefos ◽  
T. W. Andreae ◽  
D. Balis ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Optical Properties ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Scattering Coefficient ◽  
Aerosol Optical Properties ◽  
Northern Greece ◽  
Frequency Distributions ◽  
The Mean ◽  
The Impact

Abstract. Measurements of aerosol optical properties (aerosol optical depth, scattering and backscattering coefficients) have been conducted at two ground-based sites in Northern Greece, Ouranoupolis (40° 23' N, 23° 57 E, 170 m a.s.l.) and Thessaloniki (40° 38' N, 22° 57 E, 80 m a.s.l.), between 1999 and 2002. Their frequency distributions have revealed the presence of individual modes of high and low values, indicating the influence from different sources. At both sites, the mean aerosol optical depth at 500 nm was 0.23. Values increase considerably during summer when they remain persistently between 0.3 and 0.5, going up to 0.7–0.8 during specific cases. The mean value of 65±40 Mm−1 of the particle scattering coefficient at 550 nm reflects the impact of continental pollution in the regional boundary layer. Trajectory analysis has shown that higher values of aerosol optical depth and the scattering coefficient are found in the east sector (former Soviet Union countries, eastern Balkan countries), whereas cleaner conditions are found for the NW direction. The influence of Sahara dust events is clearly reflected in the Angström exponents. About 45–60% of the observed diurnal variation of the optical properties was attributed to the growth of aerosols with humidity, while the rest of the variability is in phase with the evolution of the sea-breeze cell. Local pollution is estimated to contribute 35±10% to the average aerosol optical depth at the Thessaloniki site during summer. Finally, the aerosol scale height was found to be related to the height of the boundary layer with values between 0.5–1 km during winter and up to 2.5–3 km during summer.

scholarly journals Radiative and thermodynamic responses to aerosol extinction profiles during the pre-monsoon month over South Asia

2015 ◽  
Vol 15 (12) ◽  
pp. 16901-16943 ◽  
Author(s):  
Y. Feng ◽  
V. R. Kotamarthi ◽  
R. Coulter ◽  
C. Zhao ◽  
M. Cadeddu
Keyword(s):  
Boundary Layer ◽  
South Asia ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Lower Troposphere ◽  
Longwave Radiation ◽  
Radiative Heating ◽  
Lower Atmosphere ◽  
Radiative Effects ◽  
Aerosol Radiative

Abstract. Aerosol radiative effects and thermodynamic responses over South Asia are examined with a version of the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) for March 2012. Model results of Aerosol Optical Depth (AOD) and extinction profiles are analyzed and compared to satellite retrievals and two ground-based lidars located in the northern India. The WRF-Chem model is found to underestimate the AOD during the simulated pre-monsoon month and about 83 % of the model low-bias is due to aerosol extinctions below ~2 km. Doubling the calculated aerosol extinctions below 850 hPa generates much better agreement with the observed AOD and extinction profiles averaged over South Asia. To separate the effect of absorption and scattering properties, two runs were conducted: in one run (Case I), the calculated scattering and absorption coefficients were increased proportionally, while in the second run (Case II) only the calculated aerosol scattering coefficient was increased. With the same AOD and extinction profiles, the two runs produce significantly different radiative effects over land and oceans. On the regional mean basis, Case I generates 48 % more heating in the atmosphere and 21 % more dimming at the surface than Case II. Case I also produces stronger cooling responses over the land from the longwave radiation adjustment and boundary layer mixing. These rapid adjustments offset the stronger radiative heating in Case I and lead to an overall lower-troposphere cooling up to −0.7 K day−1, which is smaller than that in Case II. Over the ocean, direct radiative effects dominate the heating rate changes in the lower atmosphere lacking such surface and lower atmosphere adjustments due to fixed sea surface temperature, and the strongest atmospheric warming is obtained in Case I. Consequently, atmospheric dynamics (boundary layer heights and meridional circulation) and thermodynamic processes (water vapor and cloudiness) are shown to respond differently between Case I and Case II underlying the importance of determining the exact portion of scattering or absorbing aerosols that lead to the underestimation of aerosol optical depth in the model. In addition, the model results suggest that both direct radiative effect and rapid thermodynamic responses need to be quantified for understanding aerosol radiative impacts.

scholarly journals Monitoring Atmospheric Aerosols Over the Urmia Lake by CALIPSO and a Ground Based Depolarized Lidar

2020 ◽  
Vol 237 ◽  
pp. 02025
Author(s):  
Hamid R. Khalesifard ◽  
Hossein Panahifar ◽  
Fatemeh Ghomashi ◽  
Salar Alizadeh ◽  
Ruhollah Moradhaseli
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Atmospheric Aerosols ◽  
Urmia Lake ◽  
Hypersaline Lake ◽  
Depolarization Ratio ◽  
Hysplit Model ◽  
Aerosol Source

The Urmia Lake, a hypersaline lake in Northwest Iran is facing a severe drying scenario. We have installed an azimuthal scanning depolarized backscatter lidar in the coast of the lake to monitor the atmospheric aerosols that may originate from the dried lake bed. We also used the CALIPSO recordings to monitor the aerosol optical depth and particulate depolarization ratio just over the lake. Recordings of the lidar and CALIPSO both show that dry salt particles can be found in the atmospheric boundary layer over the lake especially in summer times. Also CALIPSO data in synergy with HYSPLIT model show that the lake is not an intense aerosol source comparing to neighboring sources like the Mesopotamia region but it is under their influence.

scholarly journals Saharan dust contribution to the Caribbean summertime boundary layer – A lidar study during SALTRACE

2016 ◽  
Author(s):  
Silke Groß ◽  
Josef Gasteiger ◽  
Volker Freudenthaler ◽  
Thomas Müller ◽  
Daniel Sauer ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Depolarization Ratio ◽  
Angstrom Exponent ◽  
Ångström Exponent ◽  
Lidar Ratio ◽  
The Caribbean ◽  
Linear Depolarization Ratio ◽  
532 Nm

Abstract. Dual-wavelength lidar measurements with the small lidar system POLIS of the Ludwig-Maximilians-Universität München were performed during the SALTRACE experiment at Barbados in June and July 2013. Based on high accurate measurements of the linear depolarization ratio down to about 150–200 m above ground level, the dust volume fraction and the dust mass concentration within the Caribbean boundary layer can be derived. Additional information from radiosonde launches at the ground-based measurement site provide independent information of the boundary layer height and the meteorological situation within the boundary layer. We investigate the lidar derived optical properties, the lidar ratio and the particle linear depolarization ratio at 355 and 532 nm and find over all mean values and mean uncertainties of 0.04 ± 0.03 and 0.05 ± 0.04 at 355 and 532 nm, respectively, for the particle linear depolarization ratio, and 26 ± 5 sr for the lidar ratio at 355 and 532 nm. For the concentration of dust in the Caribbean boundary layer we find that most values are between 20 and 50 g/m3, and that on most days the dust contribution to total aerosol volume is about 30–40 %. Comparing the dust contribution to the columnintegrated sun-photometer measurements we see a correlation of high dust contribution, high total aerosol optical depth and a corresponding low Angström exponent, and of low dust contribution with low total aerosol optical depth and corresponding high Angström exponent. The relative humidity within the boundary layer was high with values around 80 % on most of the days.

Sign in / Sign up

Export Citation Format

Share Document