Gerrit de Leeuw - Academia.edu (original) (raw)

Papers by Gerrit de Leeuw

Research paper thumbnail of Multi-dimensional satellite observations of aerosol properties and aerosol types over three major urban clusters in eastern China

Using nine years (2007-2015) of data from passive (MODIS/Aqua) and active (CALIOP/CALIPSO) satell... more Using nine years (2007-2015) of data from passive (MODIS/Aqua) and active (CALIOP/CALIPSO) satellite measurements over China, we investigate (1) the temporal and spatial variation of aerosol properties over the Beijing-Tianjin-Hebei (BTH) region, the Yangtze River Delta (YRD) and the Pearl River Delta (PRD) and (2) the vertical distribution of aerosol types and extinction coefficients for different aerosol optical depth (AOD) and meteorological conditions. The results show the 20 different spatial patterns and seasonal variations of the AOD over the three regions. Annual time series reveal the occurrence of AOD maxima in 2011 over the YRD and in 2012 over the BTH and PRD; thereafter the AOD decreases steadily. Using the CALIOP vertical feature mask, the contributions of different aerosol types to the AOD were analysed: contributions of dust and polluted dust decrease from north to south, contributions of clean ocean, polluted continental, clean continental and smoke aerosol 25 increase from south to north. In the vertical, the peak frequency of occurrence (FO) for each aerosol type depends on region and season and varies with AOD and meteorological conditions. In general, three distinct layers are observed with the peak FO at the surface (clean continental and clean marine aerosol), at ~1 km (polluted dust and polluted continental aerosol) and at ~3 km (smoke aerosol), whereas dust aerosol may occur all over the altitude range considered in this study (from the surface up to 8 km). In this study 30 nighttime CALIOP profiles were used. The comparison with daytime profiles shows substantial differences in the FO profiles with altitude which suggest effects of boundary layer dynamics and aerosol transport on the vertical distribution of aerosol types. 1 Introduction An aerosol is technically defined as a suspension of fine solid or liquid particles in a gas; common usage 35 refers to the aerosol as the particulate component only (Seinfeld and Pandis, 1998). Aerosol particles are characterized by their diameter, chemical composition and shape (both are size-dependent), all of which vary with time and space (Unger et al., 2008; Shindell et al., 2009). Aerosol effects depend on particle size distribution, i.e. the number of particles of each size. Aerosol particles play an important role in the Earth's climate change and energy balance, directly by scattering and absorbing solar radiation and 40 indirectly by modifying cloud properties and lifetime through their ability to serve as cloud condensation

Research paper thumbnail of AATSR derived aerosol properties over land

The dual view of the Advanced Along Track Scanning Radiometer (AATSR) allows for the accurate ret... more The dual view of the Advanced Along Track Scanning Radiometer (AATSR) allows for the accurate retrieval of aerosol properties over land using an algorithm in which these two views are used to eliminate the influence of the land reflectance on the top of the atmosphere radiation. The algorithm uses the AATSR IR and visible wavebands for cloud detection and the visible wavebands for aerosol retrieval. The retrieval is based on minimizing the error function between modeled and measured TOA reflectances, using all available wavelengths. The TOA reflectances are modeled for a variety of aerosol mixtures. Hence, both the aerosol optical depth at various wavelengths (and thus the Ångström coefficient) and the mixing ratio of the dominant aerosol types can be determined. The results are evaluated by comparison with independent data: sun photometers and, when available, aerosol composition. In this contribution, the AATSR results are evaluated, based on comparisons between AATSR and MODIS AOD, and AERONET data. Results are used for assimilation in a regional scale chemistry transport model. The goal is to use satellite data for the determination of PM2.5. Other applications at TNO are in the synergisitic use with other satellites such as MSG SEVIRI and OMI.

Research paper thumbnail of Comment on Ashraf et al. Worsening situation of smog in Pakistan: A tale of three cities. Ann Med Surg (Lond) 2022, 79, 103947

Annals of Medicine and Surgery

Research paper thumbnail of Integration of Surface Reflectance and Aerosol Retrieval Algorithms for Multi-Resolution Aerosol Optical Depth Retrievals over Urban Areas

Remote Sensing

The SEMARA approach, an integration of the Simplified and Robust Surface Reflectance Estimation (... more The SEMARA approach, an integration of the Simplified and Robust Surface Reflectance Estimation (SREM) and Simplified Aerosol Retrieval Algorithm (SARA) methods, was used to retrieve aerosol optical depth (AOD) at 550 nm from a Landsat 8 Operational Land Imager (OLI) at 30 m spatial resolution, a Terra-Moderate Resolution Imaging Spectroradiometer (MODIS) at 500 m resolution, and a Visible Infrared Imaging Radiometer Suite (VIIRS) at 750 m resolution over bright urban surfaces in Beijing. The SEMARA approach coupled (1) the SREM method that is used to estimate the surface reflectance, which does not require information about water vapor, ozone, and aerosol, and (2) the SARA algorithm, which uses the surface reflectance estimated by SREM and AOD measurements obtained from the Aerosol Robotic NETwork (AERONET) site (or other high-quality AOD) as the input to estimate AOD without prior information on the aerosol optical and microphysical properties usually obtained from a look-up table...

Research paper thumbnail of Spatiotemporal changes in aerosols over Bangladesh using 18 years of MODIS and reanalysis data

Journal of Environmental Management

Research paper thumbnail of Uncertainty in Aqua-MODIS Aerosol Retrieval Algorithms During COVID-19 Lockdown

IEEE Geoscience and Remote Sensing Letters, 2022

This letter reports uncertainties in the Aqua-Moderate Resolution Imaging Spectroradiometer (MODI... more This letter reports uncertainties in the Aqua-Moderate Resolution Imaging Spectroradiometer (MODIS) Level 2 dark target (DT), deep blue (DB), and multiangle implementation of atmospheric correction (MAIAC) aerosol optical depth (AOD) during the COVID-19 lockdown period (February–May 2020) compared to the pre-COVID-19 period (February–May 2019). Validation of AOD retrievals was conducted against AErosol RObotic NETwork (AERONET) Version 3 Level 1.5 AOD data obtained from three sites located in urban (Beijing_CAMS and Beijing_RADI) and suburban (XiangHe) areas of China. The results show the poor performance of the DT and DB algorithms compared to the MAIAC algorithm, which performed better during the lockdown period. Overall, all MODIS algorithms overestimated the AOD and showed higher positive bias under high aerosol loading conditions during lockdown than during prelockdown. This is mainly attributed to the overestimation of the aerosol single-scattering albedo (SSA), which was found higher during lockdown than during the same period in 2019.

Research paper thumbnail of Himawari-8 Aerosol Optical Depth (AOD) Retrieval Using a Deep Neural Network Trained Using AERONET Observations

Remote Sensing, 2020

Spectral aerosol optical depth (AOD) estimation from satellite-measured top of atmosphere (TOA) r... more Spectral aerosol optical depth (AOD) estimation from satellite-measured top of atmosphere (TOA) reflectances is challenging because of the complicated TOA-AOD relationship and a nexus of land surface and atmospheric state variations. This task is usually undertaken using a physical model to provide a first estimate of the TOA reflectances which are then optimized by comparison with the satellite data. Recently developed deep neural network (DNN) models provide a powerful tool to represent the complicated relationship statistically. This study presents a methodology based on DNN to estimate AOD using Himawari-8 Advanced Himawari Imager (AHI) TOA observations. A year (2017) of AHI TOA observations over the Himawari-8 full disk collocated in space and time with Aerosol Robotic Network (AERONET) AOD data were used to derive a total of 14,154 training and validation samples. The TOA reflectance in all six AHI solar bands, three TOA reflectance ratios derived based on the dark-target assu...

Research paper thumbnail of Pan-Eurasian Experiment ( PEEX ) : A Framework Program on the Land-Atmosphere-Ocean-Society Interactions of the Changing Arctic – Boreal Environments

Helsinki, Helsinki, Finland; 3) Department of Forest Sciences, University of Helsinki, Helsinki, ... more Helsinki, Helsinki, Finland; 3) Department of Forest Sciences, University of Helsinki, Helsinki, Finland; 4) GAW program, World Meteorological Organization, Geneve, Switzerland; 5) Aleksanteri Institute, University of Helsinki, Helsinki, Finland; 6) Moscow State University, Moscow, Russia; 7) Aerocosmos, Moscow, Russia; 8) Tyumen State University, Tyumen, Russia. Pan-Eurasian Experiment (PEEX): A Framework Program on the Land Atmosphere Ocean Society Interactions of the Changing Arctic – Boreal Environments

Research paper thumbnail of Spatial and seasonal variations of aerosols over China from two decades of multi-satellite observations – Part 1: ATSR (1995–2011) and MODIS C6.1 (2000–2017)

Atmospheric Chemistry and Physics, 2018

Aerosol optical depth (AOD) patterns and interannual and seasonal variations over China are discu... more Aerosol optical depth (AOD) patterns and interannual and seasonal variations over China are discussed based on the AOD retrieved from the Along-Track Scanning Radiometer (ATSR-2, 1995-2002), the Advanced ATSR (AATSR, 2002-2012) (together ATSR) and the MODerate resolution Imaging Spectroradiometer (MODIS) aboard the Terra satellite (2000-2017). The AOD products used were the ATSR Dual View (ADV) v2.31 AOD and the MODIS/Terra Collection 6.1 (C6.1) merged dark target (DT) and deep blue (DB) AOD product. Together these datasets provide an AOD time series for 23 years, from 1995 to 2017. The difference between the AOD values retrieved from ATSR-2 and AATSR is small, as shown by pixel-by-pixel and monthly aggregate comparisons as well as validation results. This allows for the combination of the ATSR-2 and AATSR AOD time series into one dataset without offset correction. ADV and MODIS AOD validation results show similar high correlations with the Aerosol Robotic Network (AERONET) AOD (0.88 and 0.92, respectively), while the corresponding bias is positive for MODIS (0.06) and negative for ADV (− 0.07). Validation of the AOD products in similar conditions, when ATSR and MODIS/Terra overpasses are within 90 min of each other and when both ADV and MODIS retrieve AOD around AERONET locations, show that ADV performs better than MODIS in autumn, while MODIS performs slightly better in spring and summer. In winter, both ADV and MODIS underestimate the AERONET AOD. Similar AOD patterns are observed by ADV and MODIS in annual and seasonal aggregates as well as in time series. ADV-MODIS difference maps show that MODIS AOD is generally higher than that from ADV. Both ADV and MODIS show similar seasonal AOD behavior. The AOD maxima shift from spring in the south to summer along the eastern coast further north. The agreement between sensors regarding year-to-year AOD changes is quite good. During the period from 1995 to 2006 AOD increased in the southeast (SE) of China. Between 2006 and 2011 AOD did not change much, showing minor minima in 2008-2009. From 2011 onward AOD decreased in the SE of China. Similar patterns exist in year-toyear ADV and MODIS annual AOD tendencies in the overlapping period. However, regional differences between the ATSR and MODIS AODs are quite large. The consistency Published by Copernicus Publications on behalf of the European Geosciences Union. 11390 L. Sogacheva et al.: Spatial and seasonal variations of aerosols over China-Part 1 between ATSR and MODIS with regards to the AOD tendencies in the overlapping period is rather strong in summer, autumn and overall for the yearly average; however, in winter and spring, when there is a difference in coverage between the two instruments, the agreement between ATSR and MODIS is lower. AOD tendencies in China during the 1995-2017 period will be discussed in more detail in Part 2 (a following paper: Sogacheva et al., 2018), where a method to combine AOD time series from ADV and MODIS is introduced, and combined AOD time series are analyzed.

Research paper thumbnail of Interactions between the atmosphere, cryosphere and ecosystems at northern high latitudes

Atmospheric Chemistry and Physics Discussions, 2018

The Nordic Centre of Excellence CRAICC (CRyosphere-Atmosphere Interactions in a Changing Arctic C... more The Nordic Centre of Excellence CRAICC (CRyosphere-Atmosphere Interactions in a Changing Arctic Climate), funded by NordForsk in the years 2011-2016, was the largest joint Nordic research and innovation initiative to date, aiming to strengthen research and innovation regarding climate change issues in the Nordic Region. CRAICC gathered more than 100 scientists from all Nordic countries in a virtual Centre with the objectives to identify and quantify the major processes controlling Arctic warming and related feedback mechanisms, to outline strategies to mitigate Arctic warming and to develop Nordic Earth System modelling with a focus on the short-lived climate forcers (SLCF), including natural and anthropogenic aerosols. The outcome of CRAICC is reflected in more than 150 peer-reviewed scientific publications, most of which are in the CRAICC special-issue of the journal Atmospheric Chemistry and Physics. This manuscript presents an overview on the main scientific topics investigated in the Centre and provides the reader a state-of-the-art comprehensive summary of what has been achieved in CRAICC with links to the particular publications for further detail. Facing the vast amount of outcomes we are not claiming to cover all results from CRAICC in this manuscript but concentrate here on the main results which are related to the feedback loops in the climate change-cryosphere interaction scheme affecting the Arctic amplification. 1 Introduction Near-surface climate warming in the Arctic has proceeded at approximately twice the global average rate since 1980. This extraordinary rate of warming has been recognized since the late 1990s (Serreze et al., 2000) and has accelerated even since then (Bekryaev et al., 2010), leading to extreme events in 2016 when October-December temperatures in large parts of the Arctic were more than 5˚C above normal and daily anomalies exceeded 16˚C in many locations

Research paper thumbnail of Analysis of aerosol effects on warm clouds over the Yangtze River Delta from multi-sensor satellite observations

Atmospheric Chemistry and Physics, 2017

Research paper thumbnail of Estimates of the aerosol indirect effect over the Baltic Sea region derived from 12 years of MODIS observations

Atmospheric Chemistry and Physics, 2017

Retrieved from the Moderate Resolution Imaging Spectroradiometer (MODIS) on-board the Aqua satell... more Retrieved from the Moderate Resolution Imaging Spectroradiometer (MODIS) on-board the Aqua satellite, 12 years (2003-2014) of aerosol and cloud properties were used to statistically quantify aerosol-cloud interaction (ACI) over the Baltic Sea region, including the relatively clean Fennoscandia and the more polluted central-eastern Europe. These areas allowed us to study the effects of different aerosol types and concentrations on macro-and microphysical properties of clouds: cloud effective radius (CER), cloud fraction (CF), cloud optical thickness (COT), cloud liquid water path (LWP) and cloud-top height (CTH). Aerosol properties used are aerosol optical depth (AOD), Ångström exponent (AE) and aerosol index (AI). The study was limited to low-level water clouds in the summer. The vertical distributions of the relationships between cloud properties and aerosols show an effect of aerosols on low-level water clouds. CF, COT, LWP and CTH tend to increase with aerosol loading, indicating changes in the cloud structure, while the effective radius of cloud droplets decreases. The ACI is larger at relatively low cloud-top levels, between 900 and 700 hPa. Most of the studied cloud variables were unaffected by the lower-tropospheric stability (LTS), except for the cloud fraction. The spatial distribution of aerosol and cloud parameters and ACI, here defined as the change in CER as a function of aerosol concentration for a fixed LWP, shows positive and statistically significant ACI over the Baltic Sea and Fennoscandia, with the former having the largest values. Small negative ACI values are observed in central-eastern Europe, suggesting that large aerosol concentrations saturate the ACI.

Research paper thumbnail of 9-year spatial and temporal evolution of desert dust aerosols over South-East Asia as revealed by CALIOP

Atmospheric Chemistry and Physics Discussions, 2017

We present a 3-D climatology of the desert dust distribution over South-East Asia derived using C... more We present a 3-D climatology of the desert dust distribution over South-East Asia derived using CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) data. To distinguish desert dust from total aerosol load we apply a methodology developed in the framework of EARLINET (European Aerosol Research Lidar Network), the particle linear depolarization ratio and updated lidar ratio values suitable for Asian dust, on multiyear CALIPSO observations (01/2007–12/2015). The resulting dust product provides information on the horizontal and vertical distribution of dust aerosols over SE (South-East) Asia along with the seasonal transition of dust transport pathways. Persistent high D_AOD (Dust Aerosol Optical Depth) values, of the order of 0.6, are present over the arid and semi-arid desert regions. Dust aerosol transport (range, height and intensity) is subject to high seasonality, with highest values observed during spring for northern China (Taklimakan/Gobi deserts) ...

Research paper thumbnail of Development, Production and Evaluation of Aerosol Climate Data Records from European Satellite Observations (Aerosol_cci)

Remote Sensing, 2016

Producing a global and comprehensive description of atmospheric aerosols requires integration of ... more Producing a global and comprehensive description of atmospheric aerosols requires integration of ground-based, airborne, satellite and model datasets. Due to its complexity, aerosol monitoring requires the use of several data records with complementary information

Research paper thumbnail of Pan-Eurasian Experiment (PEEX): Towards holistic understanding of the feedbacks and interactions in the land–atmosphere–ocean–society continuum in the Northern Eurasian region

Atmospheric Chemistry and Physics Discussions, 2016

The Northern Eurasian regions and Arctic Ocean will very likely undergo substantial changes durin... more The Northern Eurasian regions and Arctic Ocean will very likely undergo substantial changes during the next decades. The arctic-boreal natural environments play a crucial role in the global climate via the albedo change, carbon sources and sinks, as well as atmospheric aerosol production via biogenic volatile organic compounds. Furthermore, it is expected that the global trade activities, demographic movement and use of natural resources will be increasing in the Arctic regions. There is a need for a novel research approach, which not only identifies and tackles the relevant multi-disciplinary research questions, but is also able to make a holistic system analysis of the expected feedbacks. In this paper, we introduce the research agenda of the Pan-Eurasian Experiment (PEEX), a multi-scale, multi-disciplinary and international program started in 2012 (<a href="https://www.atm.helsinki.fi/peex/"target="_blank">https://www.atm.helsinki.fi/peex/</a>). PE...

Research paper thumbnail of On the use of satellite remote sensing based approach for determining aerosol direct radiative effect over land: a case study over China

Atmospheric Chemistry and Physics Discussions, 2014

A satellite-based approach to derive the aerosol direct short wave (SW) radiative effect (ADRE) w... more A satellite-based approach to derive the aerosol direct short wave (SW) radiative effect (ADRE) was studied in an environment with highly variable aerosol conditions over Eastern China from March to October 2009. The method is based on using coincident SW Top of the Atmosphere (TOA) fluxes from the Clouds and the Earth's Radiant Energy System (CERES) and aerosol optical depths (AODs) from the Moderate Resolution Imaging Sectroradiometer (MODIS). The estimate for instantaneous clear sky ADRE is obtained by establishing linear regression between CERES fluxes and MODIS AODs. Even though the approach has been used in a number of studies, less focus has been paid to the method itself. In this study the main goals were first to study the method in more detail as well as it's applicability over Eastern China, and second to derive a satellite-based estimate of ADRE over the study area. Before the linear fitting, CERES fluxes were normalized to a fixed solar zenith angle, Earth–Sun d...

Research paper thumbnail of Parameterization of oceanic whitecap fraction based on satellite observations

Atmospheric Chemistry and Physics Discussions, 2015

In this study the utility of satellite-based whitecap fraction (<i>W</i>) values for ... more In this study the utility of satellite-based whitecap fraction (<i>W</i>) values for the prediction of sea spray aerosol (SSA) emission rates is explored. More specifically, the study is aimed at improving the accuracy of the sea spray source function (SSSF) derived by using the whitecap method through the reduction of the uncertainties in the parameterization of…

Research paper thumbnail of Low hygroscopic scattering enhancement of boreal aerosol and the implications for a columnar optical closure study

Atmospheric Chemistry and Physics Discussions, 2015

Published by Copernicus Publications on behalf of the European Geosciences Union. P. Zieger et al... more Published by Copernicus Publications on behalf of the European Geosciences Union. P. Zieger et al.: Scattering enhancement of boreal aerosol and columnar closure study to originate from losses of coarse and fine mode particles through dry deposition within the canopy and losses in the in situ sampling lines. In addition, elevated aerosol layers (above 3 km) from long-range transport were observed using an aerosol lidar at Kuopio, Finland, about 200 km east-northeast of Hyytiälä. These elevated layers further explain parts of the disagreement.

Research paper thumbnail of On the use of satellites to obtain information on the occurrence of natural and anthropogenic aerosols over the boreal eurasian forest

Biogeosciences Discussions, 2011

Research paper thumbnail of Uncertainty characterization of AOD for the AATSR dual and single view retrieval algorithms

Atmospheric Measurement Techniques Discussions, 2013

The uncertainty associated with satellite-retrieved aerosol properties is needed when these data ... more The uncertainty associated with satellite-retrieved aerosol properties is needed when these data are used to constrain chemical transport or climate models by using data assimilation. Global uncertainty as provided by comparison with independent groundbased observations is usually not adequate for that purpose. Rather the per-pixel uncertainty is needed. In this work we describe how these are determined in the AATSR dual and single view aerosol retrieval algorithms (ADV and ASV) which are used to retrieve aerosol optical properties from reflectance measured at the top of the atmosphere. AATSR is the Aerosol Along-Track Scanning Radiometer which flies on the European Space Agency Environmental Satellite ENVISAT. In addition, issues related to multi-year retrievals are described and discussed. The aerosol optical depth (AOD) retrieved for the year 2008 is validated versus ground-based AERONET sun photometer measurements with good agreement (r = 0.85). The comparison of the AOD uncertainties with those provided by AERONET shows that they behave well in a statistical sense. Other considerations regarding global multi-year aerosol retrievals are presented and discussed.

Research paper thumbnail of Multi-dimensional satellite observations of aerosol properties and aerosol types over three major urban clusters in eastern China

Using nine years (2007-2015) of data from passive (MODIS/Aqua) and active (CALIOP/CALIPSO) satell... more Using nine years (2007-2015) of data from passive (MODIS/Aqua) and active (CALIOP/CALIPSO) satellite measurements over China, we investigate (1) the temporal and spatial variation of aerosol properties over the Beijing-Tianjin-Hebei (BTH) region, the Yangtze River Delta (YRD) and the Pearl River Delta (PRD) and (2) the vertical distribution of aerosol types and extinction coefficients for different aerosol optical depth (AOD) and meteorological conditions. The results show the 20 different spatial patterns and seasonal variations of the AOD over the three regions. Annual time series reveal the occurrence of AOD maxima in 2011 over the YRD and in 2012 over the BTH and PRD; thereafter the AOD decreases steadily. Using the CALIOP vertical feature mask, the contributions of different aerosol types to the AOD were analysed: contributions of dust and polluted dust decrease from north to south, contributions of clean ocean, polluted continental, clean continental and smoke aerosol 25 increase from south to north. In the vertical, the peak frequency of occurrence (FO) for each aerosol type depends on region and season and varies with AOD and meteorological conditions. In general, three distinct layers are observed with the peak FO at the surface (clean continental and clean marine aerosol), at ~1 km (polluted dust and polluted continental aerosol) and at ~3 km (smoke aerosol), whereas dust aerosol may occur all over the altitude range considered in this study (from the surface up to 8 km). In this study 30 nighttime CALIOP profiles were used. The comparison with daytime profiles shows substantial differences in the FO profiles with altitude which suggest effects of boundary layer dynamics and aerosol transport on the vertical distribution of aerosol types. 1 Introduction An aerosol is technically defined as a suspension of fine solid or liquid particles in a gas; common usage 35 refers to the aerosol as the particulate component only (Seinfeld and Pandis, 1998). Aerosol particles are characterized by their diameter, chemical composition and shape (both are size-dependent), all of which vary with time and space (Unger et al., 2008; Shindell et al., 2009). Aerosol effects depend on particle size distribution, i.e. the number of particles of each size. Aerosol particles play an important role in the Earth's climate change and energy balance, directly by scattering and absorbing solar radiation and 40 indirectly by modifying cloud properties and lifetime through their ability to serve as cloud condensation

Research paper thumbnail of AATSR derived aerosol properties over land

The dual view of the Advanced Along Track Scanning Radiometer (AATSR) allows for the accurate ret... more The dual view of the Advanced Along Track Scanning Radiometer (AATSR) allows for the accurate retrieval of aerosol properties over land using an algorithm in which these two views are used to eliminate the influence of the land reflectance on the top of the atmosphere radiation. The algorithm uses the AATSR IR and visible wavebands for cloud detection and the visible wavebands for aerosol retrieval. The retrieval is based on minimizing the error function between modeled and measured TOA reflectances, using all available wavelengths. The TOA reflectances are modeled for a variety of aerosol mixtures. Hence, both the aerosol optical depth at various wavelengths (and thus the Ångström coefficient) and the mixing ratio of the dominant aerosol types can be determined. The results are evaluated by comparison with independent data: sun photometers and, when available, aerosol composition. In this contribution, the AATSR results are evaluated, based on comparisons between AATSR and MODIS AOD, and AERONET data. Results are used for assimilation in a regional scale chemistry transport model. The goal is to use satellite data for the determination of PM2.5. Other applications at TNO are in the synergisitic use with other satellites such as MSG SEVIRI and OMI.

Research paper thumbnail of Comment on Ashraf et al. Worsening situation of smog in Pakistan: A tale of three cities. Ann Med Surg (Lond) 2022, 79, 103947

Annals of Medicine and Surgery

Research paper thumbnail of Integration of Surface Reflectance and Aerosol Retrieval Algorithms for Multi-Resolution Aerosol Optical Depth Retrievals over Urban Areas

Remote Sensing

The SEMARA approach, an integration of the Simplified and Robust Surface Reflectance Estimation (... more The SEMARA approach, an integration of the Simplified and Robust Surface Reflectance Estimation (SREM) and Simplified Aerosol Retrieval Algorithm (SARA) methods, was used to retrieve aerosol optical depth (AOD) at 550 nm from a Landsat 8 Operational Land Imager (OLI) at 30 m spatial resolution, a Terra-Moderate Resolution Imaging Spectroradiometer (MODIS) at 500 m resolution, and a Visible Infrared Imaging Radiometer Suite (VIIRS) at 750 m resolution over bright urban surfaces in Beijing. The SEMARA approach coupled (1) the SREM method that is used to estimate the surface reflectance, which does not require information about water vapor, ozone, and aerosol, and (2) the SARA algorithm, which uses the surface reflectance estimated by SREM and AOD measurements obtained from the Aerosol Robotic NETwork (AERONET) site (or other high-quality AOD) as the input to estimate AOD without prior information on the aerosol optical and microphysical properties usually obtained from a look-up table...

Research paper thumbnail of Spatiotemporal changes in aerosols over Bangladesh using 18 years of MODIS and reanalysis data

Journal of Environmental Management

Research paper thumbnail of Uncertainty in Aqua-MODIS Aerosol Retrieval Algorithms During COVID-19 Lockdown

IEEE Geoscience and Remote Sensing Letters, 2022

This letter reports uncertainties in the Aqua-Moderate Resolution Imaging Spectroradiometer (MODI... more This letter reports uncertainties in the Aqua-Moderate Resolution Imaging Spectroradiometer (MODIS) Level 2 dark target (DT), deep blue (DB), and multiangle implementation of atmospheric correction (MAIAC) aerosol optical depth (AOD) during the COVID-19 lockdown period (February–May 2020) compared to the pre-COVID-19 period (February–May 2019). Validation of AOD retrievals was conducted against AErosol RObotic NETwork (AERONET) Version 3 Level 1.5 AOD data obtained from three sites located in urban (Beijing_CAMS and Beijing_RADI) and suburban (XiangHe) areas of China. The results show the poor performance of the DT and DB algorithms compared to the MAIAC algorithm, which performed better during the lockdown period. Overall, all MODIS algorithms overestimated the AOD and showed higher positive bias under high aerosol loading conditions during lockdown than during prelockdown. This is mainly attributed to the overestimation of the aerosol single-scattering albedo (SSA), which was found higher during lockdown than during the same period in 2019.

Research paper thumbnail of Himawari-8 Aerosol Optical Depth (AOD) Retrieval Using a Deep Neural Network Trained Using AERONET Observations

Remote Sensing, 2020

Spectral aerosol optical depth (AOD) estimation from satellite-measured top of atmosphere (TOA) r... more Spectral aerosol optical depth (AOD) estimation from satellite-measured top of atmosphere (TOA) reflectances is challenging because of the complicated TOA-AOD relationship and a nexus of land surface and atmospheric state variations. This task is usually undertaken using a physical model to provide a first estimate of the TOA reflectances which are then optimized by comparison with the satellite data. Recently developed deep neural network (DNN) models provide a powerful tool to represent the complicated relationship statistically. This study presents a methodology based on DNN to estimate AOD using Himawari-8 Advanced Himawari Imager (AHI) TOA observations. A year (2017) of AHI TOA observations over the Himawari-8 full disk collocated in space and time with Aerosol Robotic Network (AERONET) AOD data were used to derive a total of 14,154 training and validation samples. The TOA reflectance in all six AHI solar bands, three TOA reflectance ratios derived based on the dark-target assu...

Research paper thumbnail of Pan-Eurasian Experiment ( PEEX ) : A Framework Program on the Land-Atmosphere-Ocean-Society Interactions of the Changing Arctic – Boreal Environments

Helsinki, Helsinki, Finland; 3) Department of Forest Sciences, University of Helsinki, Helsinki, ... more Helsinki, Helsinki, Finland; 3) Department of Forest Sciences, University of Helsinki, Helsinki, Finland; 4) GAW program, World Meteorological Organization, Geneve, Switzerland; 5) Aleksanteri Institute, University of Helsinki, Helsinki, Finland; 6) Moscow State University, Moscow, Russia; 7) Aerocosmos, Moscow, Russia; 8) Tyumen State University, Tyumen, Russia. Pan-Eurasian Experiment (PEEX): A Framework Program on the Land Atmosphere Ocean Society Interactions of the Changing Arctic – Boreal Environments

Research paper thumbnail of Spatial and seasonal variations of aerosols over China from two decades of multi-satellite observations – Part 1: ATSR (1995–2011) and MODIS C6.1 (2000–2017)

Atmospheric Chemistry and Physics, 2018

Aerosol optical depth (AOD) patterns and interannual and seasonal variations over China are discu... more Aerosol optical depth (AOD) patterns and interannual and seasonal variations over China are discussed based on the AOD retrieved from the Along-Track Scanning Radiometer (ATSR-2, 1995-2002), the Advanced ATSR (AATSR, 2002-2012) (together ATSR) and the MODerate resolution Imaging Spectroradiometer (MODIS) aboard the Terra satellite (2000-2017). The AOD products used were the ATSR Dual View (ADV) v2.31 AOD and the MODIS/Terra Collection 6.1 (C6.1) merged dark target (DT) and deep blue (DB) AOD product. Together these datasets provide an AOD time series for 23 years, from 1995 to 2017. The difference between the AOD values retrieved from ATSR-2 and AATSR is small, as shown by pixel-by-pixel and monthly aggregate comparisons as well as validation results. This allows for the combination of the ATSR-2 and AATSR AOD time series into one dataset without offset correction. ADV and MODIS AOD validation results show similar high correlations with the Aerosol Robotic Network (AERONET) AOD (0.88 and 0.92, respectively), while the corresponding bias is positive for MODIS (0.06) and negative for ADV (− 0.07). Validation of the AOD products in similar conditions, when ATSR and MODIS/Terra overpasses are within 90 min of each other and when both ADV and MODIS retrieve AOD around AERONET locations, show that ADV performs better than MODIS in autumn, while MODIS performs slightly better in spring and summer. In winter, both ADV and MODIS underestimate the AERONET AOD. Similar AOD patterns are observed by ADV and MODIS in annual and seasonal aggregates as well as in time series. ADV-MODIS difference maps show that MODIS AOD is generally higher than that from ADV. Both ADV and MODIS show similar seasonal AOD behavior. The AOD maxima shift from spring in the south to summer along the eastern coast further north. The agreement between sensors regarding year-to-year AOD changes is quite good. During the period from 1995 to 2006 AOD increased in the southeast (SE) of China. Between 2006 and 2011 AOD did not change much, showing minor minima in 2008-2009. From 2011 onward AOD decreased in the SE of China. Similar patterns exist in year-toyear ADV and MODIS annual AOD tendencies in the overlapping period. However, regional differences between the ATSR and MODIS AODs are quite large. The consistency Published by Copernicus Publications on behalf of the European Geosciences Union. 11390 L. Sogacheva et al.: Spatial and seasonal variations of aerosols over China-Part 1 between ATSR and MODIS with regards to the AOD tendencies in the overlapping period is rather strong in summer, autumn and overall for the yearly average; however, in winter and spring, when there is a difference in coverage between the two instruments, the agreement between ATSR and MODIS is lower. AOD tendencies in China during the 1995-2017 period will be discussed in more detail in Part 2 (a following paper: Sogacheva et al., 2018), where a method to combine AOD time series from ADV and MODIS is introduced, and combined AOD time series are analyzed.

Research paper thumbnail of Interactions between the atmosphere, cryosphere and ecosystems at northern high latitudes

Atmospheric Chemistry and Physics Discussions, 2018

The Nordic Centre of Excellence CRAICC (CRyosphere-Atmosphere Interactions in a Changing Arctic C... more The Nordic Centre of Excellence CRAICC (CRyosphere-Atmosphere Interactions in a Changing Arctic Climate), funded by NordForsk in the years 2011-2016, was the largest joint Nordic research and innovation initiative to date, aiming to strengthen research and innovation regarding climate change issues in the Nordic Region. CRAICC gathered more than 100 scientists from all Nordic countries in a virtual Centre with the objectives to identify and quantify the major processes controlling Arctic warming and related feedback mechanisms, to outline strategies to mitigate Arctic warming and to develop Nordic Earth System modelling with a focus on the short-lived climate forcers (SLCF), including natural and anthropogenic aerosols. The outcome of CRAICC is reflected in more than 150 peer-reviewed scientific publications, most of which are in the CRAICC special-issue of the journal Atmospheric Chemistry and Physics. This manuscript presents an overview on the main scientific topics investigated in the Centre and provides the reader a state-of-the-art comprehensive summary of what has been achieved in CRAICC with links to the particular publications for further detail. Facing the vast amount of outcomes we are not claiming to cover all results from CRAICC in this manuscript but concentrate here on the main results which are related to the feedback loops in the climate change-cryosphere interaction scheme affecting the Arctic amplification. 1 Introduction Near-surface climate warming in the Arctic has proceeded at approximately twice the global average rate since 1980. This extraordinary rate of warming has been recognized since the late 1990s (Serreze et al., 2000) and has accelerated even since then (Bekryaev et al., 2010), leading to extreme events in 2016 when October-December temperatures in large parts of the Arctic were more than 5˚C above normal and daily anomalies exceeded 16˚C in many locations

Research paper thumbnail of Analysis of aerosol effects on warm clouds over the Yangtze River Delta from multi-sensor satellite observations

Atmospheric Chemistry and Physics, 2017

Research paper thumbnail of Estimates of the aerosol indirect effect over the Baltic Sea region derived from 12 years of MODIS observations

Atmospheric Chemistry and Physics, 2017

Retrieved from the Moderate Resolution Imaging Spectroradiometer (MODIS) on-board the Aqua satell... more Retrieved from the Moderate Resolution Imaging Spectroradiometer (MODIS) on-board the Aqua satellite, 12 years (2003-2014) of aerosol and cloud properties were used to statistically quantify aerosol-cloud interaction (ACI) over the Baltic Sea region, including the relatively clean Fennoscandia and the more polluted central-eastern Europe. These areas allowed us to study the effects of different aerosol types and concentrations on macro-and microphysical properties of clouds: cloud effective radius (CER), cloud fraction (CF), cloud optical thickness (COT), cloud liquid water path (LWP) and cloud-top height (CTH). Aerosol properties used are aerosol optical depth (AOD), Ångström exponent (AE) and aerosol index (AI). The study was limited to low-level water clouds in the summer. The vertical distributions of the relationships between cloud properties and aerosols show an effect of aerosols on low-level water clouds. CF, COT, LWP and CTH tend to increase with aerosol loading, indicating changes in the cloud structure, while the effective radius of cloud droplets decreases. The ACI is larger at relatively low cloud-top levels, between 900 and 700 hPa. Most of the studied cloud variables were unaffected by the lower-tropospheric stability (LTS), except for the cloud fraction. The spatial distribution of aerosol and cloud parameters and ACI, here defined as the change in CER as a function of aerosol concentration for a fixed LWP, shows positive and statistically significant ACI over the Baltic Sea and Fennoscandia, with the former having the largest values. Small negative ACI values are observed in central-eastern Europe, suggesting that large aerosol concentrations saturate the ACI.

Research paper thumbnail of 9-year spatial and temporal evolution of desert dust aerosols over South-East Asia as revealed by CALIOP

Atmospheric Chemistry and Physics Discussions, 2017

We present a 3-D climatology of the desert dust distribution over South-East Asia derived using C... more We present a 3-D climatology of the desert dust distribution over South-East Asia derived using CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) data. To distinguish desert dust from total aerosol load we apply a methodology developed in the framework of EARLINET (European Aerosol Research Lidar Network), the particle linear depolarization ratio and updated lidar ratio values suitable for Asian dust, on multiyear CALIPSO observations (01/2007–12/2015). The resulting dust product provides information on the horizontal and vertical distribution of dust aerosols over SE (South-East) Asia along with the seasonal transition of dust transport pathways. Persistent high D_AOD (Dust Aerosol Optical Depth) values, of the order of 0.6, are present over the arid and semi-arid desert regions. Dust aerosol transport (range, height and intensity) is subject to high seasonality, with highest values observed during spring for northern China (Taklimakan/Gobi deserts) ...

Research paper thumbnail of Development, Production and Evaluation of Aerosol Climate Data Records from European Satellite Observations (Aerosol_cci)

Remote Sensing, 2016

Producing a global and comprehensive description of atmospheric aerosols requires integration of ... more Producing a global and comprehensive description of atmospheric aerosols requires integration of ground-based, airborne, satellite and model datasets. Due to its complexity, aerosol monitoring requires the use of several data records with complementary information

Research paper thumbnail of Pan-Eurasian Experiment (PEEX): Towards holistic understanding of the feedbacks and interactions in the land–atmosphere–ocean–society continuum in the Northern Eurasian region

Atmospheric Chemistry and Physics Discussions, 2016

The Northern Eurasian regions and Arctic Ocean will very likely undergo substantial changes durin... more The Northern Eurasian regions and Arctic Ocean will very likely undergo substantial changes during the next decades. The arctic-boreal natural environments play a crucial role in the global climate via the albedo change, carbon sources and sinks, as well as atmospheric aerosol production via biogenic volatile organic compounds. Furthermore, it is expected that the global trade activities, demographic movement and use of natural resources will be increasing in the Arctic regions. There is a need for a novel research approach, which not only identifies and tackles the relevant multi-disciplinary research questions, but is also able to make a holistic system analysis of the expected feedbacks. In this paper, we introduce the research agenda of the Pan-Eurasian Experiment (PEEX), a multi-scale, multi-disciplinary and international program started in 2012 (<a href="https://www.atm.helsinki.fi/peex/"target="_blank">https://www.atm.helsinki.fi/peex/</a>). PE...

Research paper thumbnail of On the use of satellite remote sensing based approach for determining aerosol direct radiative effect over land: a case study over China

Atmospheric Chemistry and Physics Discussions, 2014

A satellite-based approach to derive the aerosol direct short wave (SW) radiative effect (ADRE) w... more A satellite-based approach to derive the aerosol direct short wave (SW) radiative effect (ADRE) was studied in an environment with highly variable aerosol conditions over Eastern China from March to October 2009. The method is based on using coincident SW Top of the Atmosphere (TOA) fluxes from the Clouds and the Earth's Radiant Energy System (CERES) and aerosol optical depths (AODs) from the Moderate Resolution Imaging Sectroradiometer (MODIS). The estimate for instantaneous clear sky ADRE is obtained by establishing linear regression between CERES fluxes and MODIS AODs. Even though the approach has been used in a number of studies, less focus has been paid to the method itself. In this study the main goals were first to study the method in more detail as well as it's applicability over Eastern China, and second to derive a satellite-based estimate of ADRE over the study area. Before the linear fitting, CERES fluxes were normalized to a fixed solar zenith angle, Earth–Sun d...

Research paper thumbnail of Parameterization of oceanic whitecap fraction based on satellite observations

Atmospheric Chemistry and Physics Discussions, 2015

In this study the utility of satellite-based whitecap fraction (<i>W</i>) values for ... more In this study the utility of satellite-based whitecap fraction (<i>W</i>) values for the prediction of sea spray aerosol (SSA) emission rates is explored. More specifically, the study is aimed at improving the accuracy of the sea spray source function (SSSF) derived by using the whitecap method through the reduction of the uncertainties in the parameterization of…

Research paper thumbnail of Low hygroscopic scattering enhancement of boreal aerosol and the implications for a columnar optical closure study

Atmospheric Chemistry and Physics Discussions, 2015

Published by Copernicus Publications on behalf of the European Geosciences Union. P. Zieger et al... more Published by Copernicus Publications on behalf of the European Geosciences Union. P. Zieger et al.: Scattering enhancement of boreal aerosol and columnar closure study to originate from losses of coarse and fine mode particles through dry deposition within the canopy and losses in the in situ sampling lines. In addition, elevated aerosol layers (above 3 km) from long-range transport were observed using an aerosol lidar at Kuopio, Finland, about 200 km east-northeast of Hyytiälä. These elevated layers further explain parts of the disagreement.

Research paper thumbnail of On the use of satellites to obtain information on the occurrence of natural and anthropogenic aerosols over the boreal eurasian forest

Biogeosciences Discussions, 2011

Research paper thumbnail of Uncertainty characterization of AOD for the AATSR dual and single view retrieval algorithms

Atmospheric Measurement Techniques Discussions, 2013

The uncertainty associated with satellite-retrieved aerosol properties is needed when these data ... more The uncertainty associated with satellite-retrieved aerosol properties is needed when these data are used to constrain chemical transport or climate models by using data assimilation. Global uncertainty as provided by comparison with independent groundbased observations is usually not adequate for that purpose. Rather the per-pixel uncertainty is needed. In this work we describe how these are determined in the AATSR dual and single view aerosol retrieval algorithms (ADV and ASV) which are used to retrieve aerosol optical properties from reflectance measured at the top of the atmosphere. AATSR is the Aerosol Along-Track Scanning Radiometer which flies on the European Space Agency Environmental Satellite ENVISAT. In addition, issues related to multi-year retrievals are described and discussed. The aerosol optical depth (AOD) retrieved for the year 2008 is validated versus ground-based AERONET sun photometer measurements with good agreement (r = 0.85). The comparison of the AOD uncertainties with those provided by AERONET shows that they behave well in a statistical sense. Other considerations regarding global multi-year aerosol retrievals are presented and discussed.