The Characteristics of the Aerosol Optical Depth within the Lowest Aerosol Layer over the Tibetan Plateau from 2007 to 2014

Abstract. The Tibetan Plateau (TP) is representative of typical clean atmospheric conditions. Aerosol optical depth (AOD) retrieved by Multi-angle Imaging SpectroRadiometer (MISR) is higher over Qaidam Basin than the rest of the TP all the year. Different monthly variation patterns of AOD are observed over the southern and northern TP, whereby the aerosol load is usually higher in the northern TP than in the southern part. The aerosol load over the northern part increases from April to June, peaking in May. The maximum concentration of aerosols over the southern TP occurs in July. Aerosols appear to be more easily transported over the main body of the TP across the northeastern edge rather than the southern edge. This is may be because the altitude is much lower at the northeastern edge than that of the Himalayas located along the southern edge of the TP. Three-dimensional distributions of dust, polluted dust, polluted continental and smoke are also investigated based on Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) data. Dust is found to be the most prominent aerosol type on the TP, and other types of aerosols affect the atmospheric environment slightly. A natural boundary seems to extend to an altitude of 6–8 km a.s.l., which may act as a dividing line of higher dust occurrence in the northern TP and lower dust occurrence in the southern TP, especially in spring and summer. This boundary appears around 33–35° N in the middle of the plateau, and it is possibly associated with the high altitude terrain in the same geographic location. Comparisons of CALIPSO and MISR data show that this natural boundary extending to upper troposphere is consistent with the spatial pattern of aerosol loading. The whole TP blocks the atmospheric aerosols transported from surrounding regions, and the extreme high mountains on the TP also cause an obstruction to the transport of aerosols. The aerosol distribution patterns are primarily driven by atmospheric circulation. Northerly winds prevail above the TP in spring, which also facilitates the transport of aerosols from the Tarim Basin and Qaidam Basin to the main body of the TP. Nevertheless, aerosols above the TP can originate from both the northern and southern sides of the TP during summer.

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The regional distribution characteristics of aerosol optical depth over the Tibetan Plateau

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-12065-2015 ◽

2015 ◽

Vol 15 (20) ◽

pp. 12065-12078 ◽

Cited By ~ 31

Author(s):

C. Xu ◽

Y. M. Ma ◽

C. You ◽

Z. K. Zhu

Keyword(s):

Tibetan Plateau ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Qaidam Basin ◽

Regional Distribution ◽

Atmospheric Environment ◽

Main Body ◽

The Tibetan Plateau ◽

Variation Patterns ◽

Northern Edge

Abstract. The Tibetan Plateau (TP) is representative of typical clean atmospheric conditions. Aerosol optical depth (AOD) retrieved by the Multi-angle Imaging SpectroRadiometer (MISR) is higher over Qaidam Basin than the rest of the TP throughout the year. Different monthly variation patterns of AOD are observed over the southern and northern TP, whereby the aerosol load is usually higher in the northern TP than in the southern part. The aerosol load over the northern part increases from April to June, peaking in May. The maximum concentration of aerosols over the southern TP occurs in July. Aerosols appear to be more easily transported to the main body of the TP across the northern edge rather than the southern edge. This is maybe partly because the altitude is lower at the northern edge than that of the Himalayas located along the southern edge of the TP. Three-dimensional distributions of dust, polluted dust, polluted continental aerosol and smoke are also investigated, based on Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) data. Dust is found to be the most prominent aerosol type on the TP, and other types of aerosols affect the atmospheric environment slightly. A dividing line of higher dust occurrence in the northern TP and lower dust occurrence in the southern TP can be observed clearly at an altitude of 6–8 km above sea level, especially in spring and summer. This demarcation appears around 33–35° N in the middle of the plateau, and it is possibly associated with the high-altitude terrain in the same geographic location. Comparisons of CALIPSO and MISR data show that the vertical dust occurrences are consistent with the spatial patterns of AOD. The different seasonal variation patterns between the northern and southern TP are primarily driven by atmospheric circulation, and are also related to the emission characteristics over the surrounding regions.

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Aerosol optical depth over the Tibetan Plateau and its relation to aerosols over the Taklimakan Desert

Geophysical Research Letters ◽

10.1029/2008gl034981 ◽

2008 ◽

Vol 35 (16) ◽

Cited By ~ 56

Author(s):

Xiangao Xia ◽

Pucai Wang ◽

Yuesi Wang ◽

Zhanqing Li ◽

Jinyuan Xin ◽

...

Keyword(s):

Tibetan Plateau ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Taklimakan Desert ◽

The Tibetan Plateau ◽

The Taklimakan Desert

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Anthropogenic CO<sub>2</sub> monitoring satellite mission: the need for multi-angle polarimetric observations

10.5194/amt-2020-152 ◽

2020 ◽

Author(s):

Stephanie P. Rusli ◽

Otto Hasekamp ◽

Joost aan de Brugh ◽

Guangliang Fu ◽

Yasjka Meijer ◽

...

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Zenith Angle ◽

Atmospheric Aerosols ◽

Solar Zenith Angle ◽

Added Value ◽

Aerosol Layer ◽

Satellite Mission ◽

Measurement Uncertainties ◽

Data Yield

Abstract. Atmospheric aerosols have been known to be a major source of uncertainties in CO2 concentrations retrieved from space. In this study, we investigate the added value of multi-angle polarimeter (MAP) measurements in the context of the Copernicus candidate mission for anthropogenic CO2 monitoring (CO2M). To this end, we compare aerosol-induced XCO2 errors from standard retrievals using spectrometer only (without MAP) with those from retrievals using both MAP and spectrometer. MAP observations are expected to provide information about aerosols that is useful for improving XCO2 accuracy. For the purpose of this work, we generate synthetic measurements for different atmospheric and geophysical scenes over land, based on which XCO2 retrieval errors are assessed. We show that the standard XCO2 retrieval approach that makes no use of auxiliary aerosol observations returns XCO2 errors with an overall bias of 1.12 ppm, and a spread (defined as half of the 15.9th to the 84.1th percentile range) of 2.07 ppm. The latter is far higher than the required XCO2 accuracy (0.5 ppm) and precision (0.7 ppm) of the CO2M mission. Moreover, these XCO2 errors exhibit a significantly larger bias and scatter at high aerosol optical depth, high aerosol altitude, and low solar zenith angle, which could lead to a worse performance in retrieving XCO2 from polluted areas where CO2 and aerosols are co-emitted. We proceed to determine MAP instrument specifications in terms of wavelength range, number of viewing angles, and measurement uncertainties that are required to achieve XCO2 accuracy and precision targets of the mission. Two different MAP instrument concepts are considered in this analysis. We find that for either concept, MAP measurement uncertainties on radiance and degree of linear polarization should be no more than 3 % and 0.003, respectively. Adopting the derived MAP requirements, a retrieval exercise using both MAP and spectrometer measurements of the synthetic scenes delivers XCO2 errors with an overall bias of −0.004 ppm and a spread of 0.54 ppm, implying compliance with the CO2M mission requirements; the very low bias is especially important for proper emission estimates. For the test ensemble, we find effectively no dependence of the XCO2 errors on aerosol optical depth, altitude of the aerosol layer, and solar zenith angle. These results indicate a major improvement in the retrieved XCO2 accuracy with respect to the standard retrieval approach, which could lead to a higher data yield, better global coverage, and a more comprehensive determination of CO2 sinks and sources. As such, this outcome underlines the contribution of, and therefore the need for, a MAP instrument onboard the CO2M mission.

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Using the OMI Aerosol Index and Absorption Aerosol Optical Depth to evaluate the NASA MERRA Aerosol Reanalysis

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-32177-2014 ◽

2014 ◽

Vol 14 (23) ◽

pp. 32177-32231 ◽

Cited By ~ 6

Author(s):

V. Buchard ◽

A. M. da Silva ◽

P. R. Colarco ◽

A. Darmenov ◽

C. A. Randles ◽

...

Keyword(s):

Optical Properties ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Biomass Burning ◽

Saharan Dust ◽

Aerosol Layer ◽

Anthropogenic Aerosols ◽

Aerosol Absorption ◽

Modis Aod ◽

Aerosol Index

Abstract. A radiative transfer interface has been developed to simulate the UV Aerosol Index (AI) from the NASA Goddard Earth Observing System version 5 (GEOS-5) aerosol assimilated fields. The purpose of this work is to use the AI and Aerosol Absorption Optical Depth (AAOD) derived from the Ozone Monitoring Instrument (OMI) measurements as independent validation for the Modern Era Retrospective analysis for Research and Applications Aerosol Reanalysis (MERRAero). MERRAero is based on a version of the GEOS-5 model that is radiatively coupled to the Goddard Chemistry, Aerosol, Radiation, and Transport (GOCART) aerosol module and includes assimilation of Aerosol Optical Depth (AOD) from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor. Since AI is dependent on aerosol concentration, optical properties and altitude of the aerosol layer, we make use of complementary observations to fully diagnose the model, including AOD from the Multi-angle Imaging SpectroRadiometer (MISR), aerosol retrievals from the Aerosol Robotic Network (AERONET) and attenuated backscatter coefficients from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) mission to ascertain potential misplacement of plume height by the model. By sampling dust, biomass burning and pollution events in 2007 we have compared model produced AI and AAOD with the corresponding OMI products, identifying regions where the model representation of absorbing aerosols was deficient. As a result of this study over the Saharan dust region, we have obtained a new set of dust aerosol optical properties that retains consistency with the MODIS AOD data that were assimilated, while resulting in better agreement with aerosol absorption measurements from OMI. The analysis conducted over the South African and South American biomass burning regions indicates that revising the spectrally-dependent aerosol absorption properties in the near-UV region improves the modeled-observed AI comparisons. Finally, during a period where the Asian region was mainly dominated by anthropogenic aerosols, we have performed a qualitative analysis in which the specification of anthropogenic emissions in GEOS-5 is adjusted to provide insight into discrepancies observed in AI comparisons.

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Observational evidence of particle hygroscopic growth in the upper troposphere–lower stratosphere (UTLS) over the Tibetan Plateau

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-8399-2019 ◽

2019 ◽

Vol 19 (13) ◽

pp. 8399-8406 ◽

Cited By ~ 2

Author(s):

Qianshan He ◽

Jianzhong Ma ◽

Xiangdong Zheng ◽

Xiaolu Yan ◽

Holger Vömel ◽

...

Keyword(s):

Relative Humidity ◽

Tibetan Plateau ◽

Lower Stratosphere ◽

Fine Particles ◽

Asian Summer Monsoon ◽

Radiative Properties ◽

Aerosol Layer ◽

The Tibetan Plateau ◽

Hygroscopic Growth ◽

Upper Troposphere

Abstract. We measured the vertical profiles of backscatter ratio (BSR) using the balloon-borne, lightweight Compact Optical Backscatter AerosoL Detector (COBALD) instruments above Linzhi, located in the southeastern Tibetan Plateau, in the summer of 2014. An enhanced aerosol layer in the upper troposphere–lower stratosphere (UTLS), with BSR (455 nm) > 1.1 and BSR (940 nm) > 1.4, was observed. The color index (CI) of the enhanced aerosol layer, defined as the ratio of aerosol backscatter ratios (ABSRs) at wavelengths of 940 and 455 nm, varied from 4 to 8, indicating the prevalence of fine particles with a mode radius of less than 0.1 µm. We find that unlike the very small particles (mode radius smaller than 0.04 µm) at low relative humidity (RHi < 40 %), the relatively large particles in the aerosol layer were generally very hydrophilic as their size increased dramatically with relative humidity. This result indicates that water vapor can play a very important role in increasing the size of fine particles in the UTLS over the Tibetan Plateau. Our observations provide observation-based evidence supporting the idea that aerosol particle hygroscopic growth is an important factor influencing the radiative properties of the Asian Tropopause Aerosol Layer (ATAL) during the Asian summer monsoon.

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Dust Aerosol Optical Depth Retrieval over a Desert Surface Using the SEVIRI Window Channels

Journal of Atmospheric and Oceanic Technology ◽

10.1175/2008jtecha1109.1 ◽

2009 ◽

Vol 26 (4) ◽

pp. 704-718 ◽

Cited By ~ 11

Author(s):

Bart De Paepe ◽

Steven Dewitte

Keyword(s):

Surface Temperature ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Surface Radiation ◽

Retrieval Algorithm ◽

Aerosol Layer ◽

Surface Emissivity ◽

Ir Radiation ◽

Clear Sky ◽

A Minor

Abstract The authors present a new algorithm to retrieve aerosol optical depth (AOD) over a desert using the window channels centered at 8.7, 10.8, and 12.0 μm of the Spinning Enhanced Visible and Infrared Imager (SEVIRI) instrument on board the Meteosat Second Generation satellite. The presence of dust aerosols impacts the longwave outgoing radiation, allowing the aerosols over the desert surfaces to be detected in the thermal infrared (IR) wavelengths. To retrieve the aerosol properties over land, the surface contribution to the satellite radiance measured at the top of the atmosphere has to be taken into account. The surface radiation depends on the surface temperature, which is characterized by a strong diurnal variation over the desert, and the surface emissivity, which is assumed to be constant over a time span of 24 h. The surface emissivity is based on clear-sky observations that are corrected for atmospheric absorption and emission. The clear-sky image is a composite of pixels that is characterized by the highest brightness temperature (BT) of the SEVIRI channel at 10.8 μm, and by a negative BT difference between the channels at 8.7 and 10.8 μm. Because of the lower temperatures of clouds and aerosols compared to clear-sky conditions, the authors assume that the selected pixel values are obtained for a clear-sky day. A forward model is used to simulate the thermal IR radiation transfer in the dust layer. The apparent surface radiation for the three window channels in the presence of aerosols is calculated as a function of the surface emissivity and the surface temperature, the aerosol layer temperature, and the AOD for different aerosol loadings. From these simulations two emissivity ratios, which are stored in lookup tables (LUT), are calculated. The retrieval algorithm consists of processing the clear-sky image and computing the surface emissivity, processing the instantaneous image, and computing the apparent surface radiation for the three window channels. The two emissivity ratios are computed using the radiances at 8.7 and 10.8 μm and at 8.7 and 12.0 μm, respectively. The SEVIRI AOD is obtained by the inversion of these emissivity ratios using the corresponding LUT. The algorithm is applied to a minor dust event over the Sahara between 19 and 22 June 2007. For the validation the SEVIRI AOD is compared with the AOD from the Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) along the satellite track.

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A Multi Linear Regression Model to Derive Dust PM10 in the Sahel Using AERONET Aerosol Optical Depth and CALIOP Aerosol Layer Products

Remote Sensing ◽

10.3390/rs12183099 ◽

2020 ◽

Vol 12 (18) ◽

pp. 3099

Author(s):

Jean-François Léon ◽

Nadège Martiny ◽

Sébastien Merlet

Keyword(s):

Linear Regression ◽

Regression Model ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Linear Regression Model ◽

Population Exposure ◽

Aerosol Layer ◽

Multi Linear Regression ◽

Sun Photometer ◽

The Impact

Due to a limited number of monitoring stations in Western Africa, the impact of mineral dust on PM10 surface concentrations is still poorly known. We propose a new method to retrieve PM10 dust surface concentrations from sun photometer aerosol optical depth (AOD) and CALIPSO/CALIOP Level 2 aerosol layer products. The method is based on a multi linear regression model that is trained using co-located PM10, AERONET and CALIOP observations at 3 different locations in the Sahel. In addition to the sun photometer AOD, the regression model uses the CALIOP-derived base and top altitude of the lowermost dust layer, its AOD, the columnar total and columnar dust AOD. Due to the low revisit period of the CALIPSO satellite, the monthly mean annual cycles of the parameters are used as predictor variables rather than instantaneous observations. The regression model improves the correlation coefficient between monthly mean PM10 and AOD from 0.15 (AERONET AOD only) to 0.75 (AERONET AOD and CALIOP parameters). The respective high and low PM10 concentration during the winter dry season and summer season are well produced. Days with surface PM10 above 100 μg/m3 are better identified when using the CALIOP parameters in the multi linear regression model. The number of true positives (actual and predicted concentrations above the threshold) is increased and leads to an improvement in the classification sensitivity (recall) by a factor 1.8. Our methodology can be extrapolated to the whole Sahel area provided that satellite derived AOD maps are used in order to create a new dataset on population exposure to dust events in this area.

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Anthropogenic CO<sub>2</sub> monitoring satellite mission: the need for multi-angle polarimetric observations

Atmospheric Measurement Techniques ◽

10.5194/amt-14-1167-2021 ◽

2021 ◽

Vol 14 (2) ◽

pp. 1167-1190

Author(s):

Stephanie P. Rusli ◽

Otto Hasekamp ◽

Joost aan de Brugh ◽

Guangliang Fu ◽

Yasjka Meijer ◽

...

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Zenith Angle ◽

Atmospheric Aerosols ◽

Solar Zenith Angle ◽

Added Value ◽

Aerosol Layer ◽

Satellite Mission ◽

Measurement Uncertainties ◽

Data Yield

Abstract. Atmospheric aerosols have been known to be a major source of uncertainties in CO2 concentrations retrieved from space. In this study, we investigate the added value of multi-angle polarimeter (MAP) measurements in the context of the Copernicus Anthropogenic Carbon Dioxide Monitoring (CO2M) mission. To this end, we compare aerosol-induced XCO2 errors from standard retrievals using a spectrometer only (without MAP) with those from retrievals using both MAP and a spectrometer. MAP observations are expected to provide information about aerosols that is useful for improving XCO2 accuracy. For the purpose of this work, we generate synthetic measurements for different atmospheric and geophysical scenes over land, based on which XCO2 retrieval errors are assessed. We show that the standard XCO2 retrieval approach that makes no use of auxiliary aerosol observations returns XCO2 errors with an overall bias of 1.12 ppm and a spread (defined as half of the 15.9–84.1 percentile range) of 2.07 ppm. The latter is far higher than the required XCO2 accuracy (0.5 ppm) and precision (0.7 ppm) of the CO2M mission. Moreover, these XCO2 errors exhibit a significantly larger bias and scatter at high aerosol optical depth, high aerosol altitude, and low solar zenith angle, which could lead to worse performance in retrieving XCO2 from polluted areas where CO2 and aerosols are co-emitted. We proceed to determine MAP instrument specifications in terms of wavelength range, number of viewing angles, and measurement uncertainties that are required to achieve XCO2 accuracy and precision targets of the mission. Two different MAP instrument concepts are considered in this analysis. We find that for either concept, MAP measurement uncertainties on radiance and degree of linear polarization should be no more than 3 % and 0.003, respectively. A retrieval exercise using MAP and spectrometer measurements of the synthetic scenes is carried out for each of the two MAP concepts. The resulting XCO2 errors have an overall bias of −0.004 ppm and a spread of 0.54 ppm for one concept, and a bias of 0.02 ppm and a spread of 0.52 ppm for the other concept. Both are compliant with the CO2M mission requirements; the very low bias is especially important for proper emission estimates. For the test ensemble, we find effectively no dependence of the XCO2 errors on aerosol optical depth, altitude of the aerosol layer, and solar zenith angle. These results indicate a major improvement in the retrieved XCO2 accuracy with respect to the standard retrieval approach, which could lead to a higher data yield, better global coverage, and a more comprehensive determination of CO2 sinks and sources. As such, this outcome underlines the contribution of, and therefore the need for, a MAP instrument aboard the CO2M mission.

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Daytime aerosol optical depth above low-level clouds is similar to that in adjacent clear skies at the same heights: airborne observation above the southeast Atlantic

10.5194/acp-2019-1007 ◽

2020 ◽

Author(s):

Yohei Shinozuka ◽

Meloë S. Kacenelenbogen ◽

Sharon P. Burton ◽

Steven G. Howell ◽

Paquita Zuidema ◽

...

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Wavelength Dependence ◽

Single Scattering ◽

Airborne Lidar ◽

Aerosol Layer ◽

Low Level ◽

Satellite Retrieval ◽

Biomass Burning Aerosol ◽

The Difference

Abstract. To help satellite retrieval of aerosols and studies of their radiative effects, we demonstrate that daytime 532 nm aerosol optical depth over low-level clouds is similar to that in neighboring clear skies at the same heights in recent airborne lidar and sunphotometer observations above the southeast Atlantic. The mean AOD difference is between 0 and −0.01, when comparing the two sides, each up to 20 km wide, of cloud edges. The difference is not statistically significant according to a paired t-test. Systematic differences in the wavelength dependence of AOD and in situ single scattering albedo are also minute. These results hold regardless of the vertical distance between cloud top and aerosol layer bottom. AOD aggregated over ~ 2° grid boxes for each of September 2016, August 2017 and October 2018 also shows little correlation with the presence of low-level clouds. We posit that a satellite retrieval artifact is entirely responsible for a previous finding of generally smaller AOD over clouds (Chung et al., 2016), at least for the region and season of our study. Our results also suggest that the same values can be assumed for the intensive properties of free-tropospheric biomass-burning aerosol regardless of whether clouds exist below.

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