scholarly journals Aerosol profile information from high resolution oxygen A-Band measurements from space

2014 ◽  
Vol 7 (6) ◽  
pp. 6021-6063
Author(s):  
A. Geddes ◽  
H. Bösch
Keyword(s):  
Boundary Layer ◽  
Information Content ◽  
A Priori ◽  
Aerosol Layer ◽  
Free Troposphere ◽  
Limited Information ◽  
High Coverage ◽  
A Value ◽  
Aerosol Distribution ◽  
Satellite Sensors

Abstract. Aerosols are an important factor of the Earth climatic system and they play a key role for air quality and public health. Observations of the oxygen A-Band at 760 nm can provide information on the vertical distribution of aerosols from passive satellite sensors, that can be of great interest for operational monitoring applications with high coverage if the aerosol information is obtained with sufficient precision, accuracy and vertical resolution. To address this issue, retrieval simulations of the aerosol vertical profile retrieval from O2 A Band observations by GOSAT, the upcoming OCO-2 and Sentinel 5-P mission and the proposed CarbonSat mission have been carried out. Precise retrievals of AOD within the boundary layer were found to favour low resolution, high SNR instruments such as Sentinel-5 P, whereas higher resolution instruments such as OCO-2 showed greater performance at higher altitudes and in information content above the boundary layer. Accurate retrievals of the AOD in the 0–2 km range appears difficult from all studied instruments and the retrieval errors typically exceed a value of 0.05. Constraining the surface albedo is a promising and effective way of improving the retrieval of aerosol, but the required level of a priori knowledge is very high. Due to the limited information content of the aerosol profile retrieval, the use of a parameterised aerosol distribution has been assessed and we show that the AOD and height of an aerosol layer can be retrieved well if the aerosol layer is uplifted to the free troposphere but errors are often large for aerosol layers in the boundary layer. Additional errors will be introduced by incorrect assumptions on surface pressure and aerosol type which can both bias retrieved AOD and height by up to 40%. We conclude the aerosol profile retrievals from O2 A Band using existing or upcoming satellite sensors will only provide limited information on aerosols in the boundary layer but such observations can be of great value for observing and mapping aerosol plumes in the free troposphere.

scholarly journals Tropospheric aerosol profile information from high-resolution oxygen A-band measurements from space

2015 ◽  
Vol 8 (2) ◽  
pp. 859-874 ◽  
Author(s):  
A. Geddes ◽  
H. Bösch
Keyword(s):  
Boundary Layer ◽  
Information Content ◽  
High Signal ◽  
Aerosol Layer ◽  
Free Troposphere ◽  
Limited Information ◽  
Aerosol Distribution ◽  
Spatial Coverage ◽  
Tropospheric Aerosol ◽  
Satellite Sensors

Abstract. Aerosols are an important factor in the Earth climatic system and they play a key role in air quality and public health. Observations of the oxygen A-band at 760 nm can provide information on the vertical distribution of aerosols from passive satellite sensors that can be of great interest for operational monitoring applications with high spatial coverage if the aerosol information is obtained with sufficient precision, accuracy and vertical resolution. To address this issue, retrieval simulations of the aerosol vertical profile retrieval from O2 A-band observations by GOSAT, the upcoming Orbiting Carbon Observatory-2 (OCO-2) and Sentinel 5-P missions, and the proposed CarbonSat mission have been carried out. Precise retrievals of aerosol optical depth (AOD) within the boundary layer were found to favour low-resolution, high signal-to-noise instruments such as Sentinel-5 P, whereas higher-resolution instruments such as OCO-2 showed greater performance at higher altitudes and in information content above the boundary layer. Retrieval of the AOD in the 0–2 km range with precision appears difficult from all studied instruments and the retrieval errors typically exceed a value of 0.05 for AODs up to 0.3. Constraining the surface albedo is a promising and effective way of improving the retrieval of aerosol, but the accuracy of the required prior knowledge is very high. Due to the limited information content of the aerosol profile retrieval, the use of a parameterised aerosol distribution is assessed, and we show that the AOD and height of an aerosol layer can be retrieved well if the aerosol layer is uplifted to the free troposphere; however, errors are often large for aerosol layers in the boundary layer. Additional errors are introduced by incorrect assumptions on surface pressure and aerosol mixture, which can both bias retrieved AOD and height by up to 45%. In addition, assumptions of the boundary layer temperature are found to yield an additional error of up to 8%. We conclude that the aerosol profile retrievals from O2 A-band using existing or upcoming satellite sensors will only provide limited information on aerosols in the boundary layer but such observations can be of great value for observing and mapping aerosol plumes in the free troposphere.

scholarly journals Are EARLINET and AERONET climatologies consistent? The case of Thessaloniki, Greece

2018 ◽  
Vol 18 (16) ◽  
pp. 11885-11903 ◽  
Author(s):  
Nikolaos Siomos ◽  
Dimitris S. Balis ◽  
Kalliopi A. Voudouri ◽  
Eleni Giannakaki ◽  
Maria Filioglou ◽  
...  
Keyword(s):  
Boundary Layer ◽  
A Priori ◽  
Free Troposphere ◽  
Climatological Data ◽  
Annual Cycles ◽  
Passive Remote Sensing ◽  
Dust Component ◽  
Remote Sensing Techniques ◽  
Sampling Schedule

Abstract. In this study we investigate the climatological behavior of the aerosol optical properties over Thessaloniki during the years 2003–2017. For this purpose, measurements of two independent instruments, a lidar and a sunphotometer, were used. These two instruments represent two individual networks, the European Lidar Aerosol Network (EARLINET) and the Aerosol Robotic Network (AERONET). They include different measurement schedules. Fourteen years of lidar and sunphotometer measurements were analyzed, independently of each other, in order to obtain the annual cycles and trends of various optical and geometrical aerosol properties in the boundary layer, in the free troposphere, and for the whole atmospheric column. The analysis resulted in consistent statistically significant and decreasing trends of aerosol optical depth (AOD) at 355 nm of −23.2 and −22.3 % per decade in the study period over Thessaloniki for the EARLINET and the AERONET datasets, respectively. Therefore, the analysis indicates that the EARLINET sampling schedule can be quite effective in producing data that can be applied to long-term climatological studies. It is also shown that the observed decreasing trend is mainly attributed to changes in the aerosol load inside the boundary layer. Seasonal profiles of the most dominant aerosol mixture types observed over Thessaloniki have been generated from the lidar data. The higher values of the vertically resolved extinction coefficient at 355 nm appear in summer, while the lower ones appear in winter. The dust component is more dominant in the free troposphere than in the boundary layer during summer. The biomass burning layers tend to arrive in the free troposphere during spring and summer. This kind of information can be quite useful for applications that require a priori aerosol profiles. For instance, they can be utilized in models that require aerosol climatological data as input, in the development of algorithms for satellite products, and also in passive remote-sensing techniques that require knowledge of the aerosol vertical distribution.

scholarly journals Ability of the MAX-DOAS method to derive profile information for NO<sub>2</sub>: can the boundary layer and free troposphere be separated?

2011 ◽  
Vol 4 (12) ◽  
pp. 2659-2684 ◽  
Author(s):  
T. Vlemmix ◽  
A. J. M. Piters ◽  
A. J. C. Berkhout ◽  
L. F. L. Gast ◽  
P. Wang ◽  
...  
Keyword(s):  
Boundary Layer ◽  
A Priori ◽  
Optical Absorption Spectroscopy ◽  
Retrieval Algorithm ◽  
Free Troposphere ◽  
Average Difference ◽  
Retrieval Models ◽  
Error Sources ◽  
Profile Information ◽  
Tropospheric No2

Abstract. Multiple Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) instruments can measure from the ground the absorption by nitrogen dioxide (NO2) of scattered sunlight seen in multiple viewing directions. This paper studies the potential of this technique to derive the vertical distribution of NO2 in the troposphere. Such profile information is essential for detailed comparisons of MAX-DOAS retrievals with other measurement techniques for NO2, e.g. with a lidar or from space. The retrieval algorithm used is based on a pre-calculated look-up table and assumes homogeneous mixing of aerosols and NO2 in layers extending from the surface to a variable height. Two retrieval models are compared: one including and one excluding an elevated NO2 layer at a fixed altitude in the free troposphere. An ensemble technique is applied to derive retrieval uncertainties. Sensitivity studies demonstrate that NO2 in the free troposphere can only be retrieved accurately if: (i) the retrieved boundary layer profiles for aerosols and NO2 correspond to the real ones, (ii) if the right a-priori choice is made for the (average) height of free tropospheric NO2, and (iii) if all other error sources are very low. It is shown that retrieval models that are capable of accurate NO2 retrievals in the free troposphere, i.e. models not constrained too much by a-priori assumptions, have as a major disadvantage that they will frequently find free tropospheric NO2, also when it is not present in reality. This is a consequence of the fact that NO2 in the free troposphere is poorly constrained by the MAX-DOAS observations, especially for high aerosol optical thickness values in the boundary layer. Retrieval of free tropospheric NO2 is therefore sensitive to a large number of error sources. For this reason it is advised to firmly constrain free tropospheric NO2 in MAX-DOAS retrieval models used for applications such as satellite validation. This effectively makes free tropospheric NO2 a source of error for MAX-DOAS retrieval of NO2 profiles in the boundary layer. A comparison was performed with independent data, based on MAX-DOAS observations done at the CINDI campaign, held in the Netherlands in 2009. Comparison with lidar partial tropospheric NO2 columns showed a correlation of 0.78, and an average difference of 0.1× 1015 molec cm−2. The diurnal evolution of the NO2 volume mixing ratio measured by in-situ monitors at the surface and averaged over five days with cloud-free mornings, compares well to the MAX-DOAS retrieval: a correlation was found of 0.94, and an average difference of 0.04 ppb.

scholarly journals Are EARLINET and AERONET climatologies consistent? The case of Thessaloniki, Greece

2018 ◽  
Author(s):  
Nikolaos Siomos ◽  
Dimitris S. Balis ◽  
Kalliopi A. Voudouri ◽  
Eleni Giannakaki ◽  
Maria Filioglou ◽  
...  
Keyword(s):  
Boundary Layer ◽  
A Priori ◽  
Free Troposphere ◽  
Climatological Data ◽  
Annual Cycles ◽  
Passive Remote Sensing ◽  
Dust Component ◽  
Remote Sensing Techniques ◽  
Sampling Schedule ◽  
Aerosol Properties

Abstract. In this study we investigate the climatological behavior of the aerosol optical properties over Thessaloniki during the years 2003–2017. For this purpose, measurements of two independent instruments, a lidar and a sunphotomer, were deployed. These two instruments represent two individual networks, the European Lidar Aerosol Network (EARLINET) and the Aerosol Robotic Network (AERONET). They include different measurement schedules. Fourteen years of lidar and sunphotometer measurements were analyzed in order to obtain the annual cycles and trends of multiple optical and geometrical aerosol properties in the boundary layer, in the free troposphere and for the whole atmospheric column. The analysis resulted in consistent statistically significant and decreasing AOD 355 nm trends of −21.0 % and −16.6 % per decade in the study period over Thessaloniki for the EARLINET and the AERONET datasets respectively. Therefore, the analysis implies that the EARLINET sampling schedule can be quite effective in producing data that can be applied to climatological studies. It has also been confirmed that the observed decreasing trend is mainly attributed to changes in the aerosol properties inside the boundary layer. Seasonal profiles of the most dominant aerosol mixture types have been generated from the lidar data. The higher values of the extinction at 355 nm appear in summer, while the lower ones appear in winter. The dust component is much more dominant in the free troposphere than in the boundary layer during summer while the opposite is observed in winter. The strongest biomass burning episodes tend to occur during summer in the free troposphere and are probably attributed to wildfires rather than agricultural fires that are predominant during spring and autumn. This kind of information can be quite useful for applications that require a priori aerosol profiles. For instance, they can be utilized in models that require aerosol climatological data as input, in the development of algorithms for satellite products, and also in passive remote sensing techniques that require knowledge of the aerosol vertical distribution.

scholarly journals Southeast Pacific stratocumulus clouds, precipitation and boundary layer structure sampled along 20° S during VOCALS-REx

2010 ◽  
Vol 10 (21) ◽  
pp. 10639-10654 ◽  
Author(s):  
C. S. Bretherton ◽  
R. Wood ◽  
R. C. George ◽  
D. Leon ◽  
G. Allen ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Liquid Water ◽  
Vertical Structure ◽  
Layer Structure ◽  
Cloud Droplet ◽  
Free Troposphere ◽  
Liquid Water Path ◽  
Typical Structure ◽  
Southeast Pacific ◽  
Over The Top

Abstract. Multiplatform airborne, ship-based, and land-based observations from 16 October–15 November 2008 during the VOCALS Regional Experiment (REx) are used to document the typical structure of the Southeast Pacific stratocumulus-topped boundary layer and lower free troposphere on a~transect along 20° S between the coast of Northern Chile and a buoy 1500 km offshore. Strong systematic gradients in clouds, precipitation and vertical structure are modulated by synoptically and diurnally-driven variability. The boundary layer is generally capped by a strong (10–12 K), sharp inversion. In the coastal zone, the boundary layer is typically 1 km deep, fairly well mixed, and topped by thin, nondrizzling stratocumulus with accumulation-mode aerosol and cloud droplet concentrations exceeding 200 cm−3. Far offshore, the boundary layer depth is typically deeper (1600 m) and more variable, and the vertical structure is usually decoupled. The offshore stratocumulus typically have strong mesoscale organization, much higher peak liquid water paths, extensive drizzle, and cloud droplet concentrations below 100 cm−3, sometimes with embedded pockets of open cells with lower droplet concentrations. The lack of drizzle near the coast is not just a microphysical response to high droplet concentrations; smaller cloud depth and liquid water path than further offshore appear comparably important. Moist boundary layer air is heated and mixed up along the Andean slopes, then advected out over the top of the boundary layer above adjacent coastal ocean regions. Well offshore, the lower free troposphere is typically much drier. This promotes strong cloud-top radiative cooling and stronger turbulence in the clouds offshore. In conjunction with a slightly cooler free troposphere, this may promote stronger entrainment that maintains the deeper boundary layer seen offshore. Winds from ECMWF and NCEP operational analyses have an rms difference of only 1 m s−1 from collocated airborne leg-mean observations in the boundary layer and 2 m s−1 above the boundary layer. This supports the use of trajectory analysis for interpreting REx observations. Two-day back-trajectories from the 20° S transect suggest that eastward of 75° W, boundary layer (and often free-tropospheric) air has usually been exposed to South American coastal aerosol sources, while at 85° W, neither boundary-layer or free-tropospheric air has typically had such contact.

scholarly journals Assessment of mixed-layer height estimation from single-wavelength ceilometer profiles

2017 ◽  
Vol 10 (10) ◽  
pp. 3963-3983 ◽  
Author(s):  
Travis N. Knepp ◽  
James J. Szykman ◽  
Russell Long ◽  
Rachelle M. Duvall ◽  
Jonathan Krug ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Data Collection ◽  
Mixed Layer ◽  
A Priori ◽  
Processing Algorithm ◽  
Height Measurement ◽  
Layer Height ◽  
Network Operation ◽  
Mixed Layer Height ◽  
The Impact

Abstract. Differing boundary/mixed-layer height measurement methods were assessed in moderately polluted and clean environments, with a focus on the Vaisala CL51 ceilometer. This intercomparison was performed as part of ongoing measurements at the Chemistry And Physics of the Atmospheric Boundary Layer Experiment (CAPABLE) site in Hampton, Virginia and during the 2014 Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) field campaign that took place in and around Denver, Colorado. We analyzed CL51 data that were collected via two different methods (BLView software, which applied correction factors, and simple terminal emulation logging) to determine the impact of data collection methodology. Further, we evaluated the STRucture of the ATmosphere (STRAT) algorithm as an open-source alternative to BLView (note that the current work presents an evaluation of the BLView and STRAT algorithms and does not intend to act as a validation of either). Filtering criteria were defined according to the change in mixed-layer height (MLH) distributions for each instrument and algorithm and were applied throughout the analysis to remove high-frequency fluctuations from the MLH retrievals. Of primary interest was determining how the different data-collection methodologies and algorithms compare to each other and to radiosonde-derived boundary-layer heights when deployed as part of a larger instrument network. We determined that data-collection methodology is not as important as the processing algorithm and that much of the algorithm differences might be driven by impacts of local meteorology and precipitation events that pose algorithm difficulties. The results of this study show that a common processing algorithm is necessary for light detection and ranging (lidar)-based MLH intercomparisons and ceilometer-network operation, and that sonde-derived boundary layer heights are higher (10–15 % at midday) than lidar-derived mixed-layer heights. We show that averaging the retrieved MLH to 1 h resolution (an appropriate timescale for a priori data model initialization) significantly improved the correlation between differing instruments and differing algorithms.

scholarly journals Surface fluxes of bromoform and dibromomethane over the tropical western Pacific inferred from airborne in situ measurements

2017 ◽  
Author(s):  
Liang Feng ◽  
Paul I. Palmer ◽  
Robyn Butler ◽  
Stephen J. Andrews ◽  
Elliot L. Atlas ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Chemistry ◽  
Marine Boundary Layer ◽  
Current Knowledge ◽  
A Priori ◽  
Surface Fluxes ◽  
Western Pacific ◽  
Study Region ◽  
The Western Pacific ◽  
Aircraft Data

Abstract. We infer surface fluxes of bromoform (CHBr3) and dibromoform (CH2Br2) from aircraft observations over the western Pacific using a tagged version of the GEOS-Chem global 3-D atmospheric chemistry model and a Maximum A Posteriori inverse model. The distribution of a priori ocean emissions of these gases are reasonably consistent with observed atmospheric mole fractions of CHBr3 (r = 0.62) and CH2Br2 (r = 0.38). These a priori emissions result in a positive model bias in CHBr3 peaking in the marine boundary layer, but capture observed values of CH2Br2 with no significant bias by virtue of its longer atmospheric lifetime. Using GEOS-Chem, we find that observed variations in atmospheric CHBr3 are determined equally by sources over the western Pacific and those outside the study region, but observed variations in CH2Br2 are determined mainly by sources outside the western Pacific. Numerical closed-loop experiments show that the spatial and temporal distribution of boundary layer aircraft data have the potential to substantially improve current knowledge of these fluxes, with improvements related to data density. Using the aircraft data, we estimate aggregated regional fluxes of 3.6 ± 0.3 × 108 g/month and 0.7 ± 0.1 × 108 g/month for CHBr3 and CH2Br2 over 130°–155° E and 0°–12° N, respectively, which represent reductions of 20–40 % and substantial spatial deviations from the a priori inventory. We find no evidence to support a robust linear relationship between CHBr3 and CH2Br2 oceanic emissions, as used by previous studies.

scholarly journals Aerosol distribution around Svalbard during intense easterly winds

2010 ◽  
Vol 10 (4) ◽  
pp. 1473-1490 ◽  
Author(s):  
A. Dörnbrack ◽  
I. S. Stachlewska ◽  
C. Ritter ◽  
R. Neuber
Keyword(s):  
Sea Salt ◽  
Airborne Lidar ◽  
The Arctic ◽  
Aerosol Layer ◽  
Atmospheric Conditions ◽  
Sea Salt Aerosols ◽  
Aerosol Distribution ◽  
Weather Situation ◽  
Low Level Jet ◽  
Aerosol Plume

Abstract. This paper reports on backscatter and depolarization measurements by an airborne lidar in the Arctic during the ASTAR 2004 campaign. A unique weather situation facilitated the observation of the aerosol concentration under strongly forced atmospheric conditions. The vigorous easterly winds distorted the flow past Svalbard in such a way that mesoscale features were visible in the remote-sensing observations: The formation of a well-mixed aerosol layer inside the Adventdalen and the subsequent thinning of the aerosol plume were observed over the Isfjorden. Additionally, mobilization of sea salt aerosols due to a coastal low-level jet at the northern tip of Svalbard resulted in a sloped boundary layer toward north. Mesoscale numerical modelling was applied to identify the sources of the aerosol particles and to explain the observed patterns.

scholarly journals Dome effect of black carbon and its key influencing factors: A one-dimensional modelling study

2017 ◽  
Author(s):  
Zilin Wang ◽  
Xin Huang ◽  
Aijun Ding
Keyword(s):  
Boundary Layer ◽  
Air Pollution ◽  
Black Carbon ◽  
Rural Areas ◽  
Land Surface ◽  
Critical Role ◽  
Aerosol Layer ◽  
Near Surface ◽  
Haze Pollution ◽  
The Impact

Abstract. Black carbon (BC) has been identified to play a critical role in aerosol-planet boundary layer (PBL) interaction and further deterioration of near-surface air pollution in megacities, which has been named as its dome effect. However, the impacts of key factors that influence this effect, such as the vertical distribution and aging processes of BC, and also the underlying land surface, have not been quantitatively explored yet. Here, based on available in-situ measurements of meteorology and atmospheric aerosols together with the meteorology-chemistry online coupled model, WRF-Chem, we conduct a set of parallel simulations to quantify the roles of these factors in influencing the BC's dome effect and surface haze pollution, and discuss the main implications of the results to air pollution mitigation in China. We found that the impact of BC on PBL is very sensitive to the altitude of aerosol layer. The upper level BC, especially those near the capping inversion, is more essential in suppressing the PBL height and weakening the turbulence mixing. The dome effect of BC tends to be significantly intensified as BC aerosol mixed with scattering aerosols during winter haze events, resulting in a decrease of PBL height by more than 25 %. In addition, the dome effect is more substantial (up to 15 %) in rural areas than that in the urban areas with the same BC loading, indicating an unexpected regional impact of such kind of effect to air quality in countryside. This study suggests that China's regional air pollution would greatly benefit from BC emission reductions, especially those from the elevated sources from the chimneys and also the domestic combustions in rural areas, through weakening the aerosol-boundary layer interactions that triggered by BC.

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