A synergy of linear model and wavelet analysis towards space-time characterization of aerosol optical depth (AOD) during pre-monsoon season (2007–2016) over Indian sub-continent

Abstract. The high spatial and temporal variability of aerosols make networks capable of measuring their properties in near real time of high scientific interest. In this work we present and discuss results of an aerosol optical depth algorithm to be used in the European Brewer Network, which provides data in near real time of more than 30 spectrophotometers located from Tamanrasset (Algeria) to Kangerlussuaq (Greenland). Using data from the Brewer Intercomparison Campaigns in the years 2013 and 2015, and the period in between, plus comparisons with Cimel sunphotometers and UVPFR instruments, we check the precision, stability, and uncertainty of the Brewer AOD in the ultraviolet range from 300 to 320 nm. Our results show a precision better than 0.01, an uncertainty of less than 0.05, and a stability similar to that of the ozone measurements for well-maintained instruments. We also discuss future improvements to our algorithm with respect to the input data, their processing, and the characterization of the Brewer instruments for the measurement of aerosols.

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Measurement of aerosol optical depth and sub-visual cloud detection using the optical depth sensor (ODS)

Atmospheric Measurement Techniques ◽

10.5194/amt-9-455-2016 ◽

2016 ◽

Vol 9 (2) ◽

pp. 455-467 ◽

Cited By ~ 5

Author(s):

D. Toledo ◽

P. Rannou ◽

J.-P. Pommereau ◽

A. Sarkissian ◽

T. Foujols

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Diffuse Radiation ◽

Dust Storms ◽

Saharan Dust ◽

Cloud Detection ◽

Depth Sensor ◽

Data Set ◽

Good Agreement

Abstract. A small and sophisticated optical depth sensor (ODS) has been designed to work in the atmosphere of Mars. The instrument measures alternatively the diffuse radiation from the sky and the attenuated direct radiation from the Sun on the surface. The principal goals of ODS are to retrieve the daily mean aerosol optical depth (AOD) and to detect very high and optically thin clouds, crucial parameters in understanding the Martian meteorology and climatology. The detection of clouds is undertaken at twilight, allowing the detection and characterization of clouds with opacities below 0.03 (sub-visual clouds). In addition, ODS is capable to retrieve the aerosol optical depth during nighttime from moonlight measurements. Recently, ODS has been selected at the METEO meteorological station on board the ExoMars 2018 Lander. In order to study the performance of ODS under Mars-like conditions as well as to evaluate the retrieval algorithms for terrestrial measurements, ODS was deployed in Ouagadougou (Africa) between November 2004 and October 2005, a Sahelian region characterized by its high dust aerosol load and the frequent occurrence of Saharan dust storms. The daily average AOD values retrieved by ODS were compared with those provided by a CIMEL sunphotometer of the AERONET (Aerosol Robotic NETwork) network localized at the same location. Results represent a good agreement between both ground-based instruments, with a correlation coefficient of 0.77 for the whole data set and 0.94 considering only the cloud-free days. From the whole data set, a total of 71 sub-visual cirrus (SVC) were detected at twilight with opacities as thin as 1.10−3 and with a maximum of occurrence at altitudes between 14 and 20 km. Although further optimizations and comparisons of ODS terrestrial measurements are required, results indicate the potential of these measurements to retrieve the AOD and detect sub-visual clouds.

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Spectral aerosol optical depth characterization of desert dust during SAMUM 2006

Tellus B ◽

10.1111/j.1600-0889.2008.00382.x ◽

2009 ◽

Vol 61 (1) ◽

pp. 216-228 ◽

Cited By ~ 45

Author(s):

C. Toledano ◽

M. Wiegner ◽

M. Garhammer ◽

M. Seefeldner ◽

J. Gasteiger ◽

...

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Desert Dust

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Sunphotometry of the 2006–2007 aerosol optical/radiative properties at the Himalayan Nepal Climate Observatory – Pyramid (5079 m a.s.l.)

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-10-1193-2010 ◽

2010 ◽

Vol 10 (1) ◽

pp. 1193-1220 ◽

Cited By ~ 11

Author(s):

G. P. Gobbi ◽

F. Angelini ◽

P. Bonasoni ◽

G. P. Verza ◽

A. Marinoni ◽

...

Keyword(s):

High Altitude ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Radiative Forcing ◽

Monsoon Season ◽

Good Reason ◽

Single Scattering ◽

Radiative Properties ◽

Mountain Range ◽

Monsoon Period

Abstract. In spite of being located at the heart of the highest mountain range in the world, the Himalayan Nepal Climate Observatory (5079 m a.s.l.) at the Ev-K2-CNR Pyramid is shown to be affected by the advection of pollution aerosols from the populated regions of southern Nepal and the Indo-Gangetic plains. Such an impact is observed along most of the period April 2006–March 2007 addressed here, with a minimum in the monsoon season. Backtrajectory-analysis indicates long-range transport episodes occurring in this period to originate mainly in the West Asian deserts. At this high altitude site, the measured aerosol optical depth is observed to be: 1) about one order of magnitude lower than the one measured at Gandhi College (60 m a.s.l.), in the Indo-Gangetic basin, and 2) maximum during the monsoon period, due to the presence of elevated (cirrus-like) particle layers. Assessment of the aerosol radiative forcing results to be hampered by the persistent presence of these high altitude particle layers, which impede a continuous measurement of both the aerosol optical depth and its radiative properties from sky radiance inversions. Even though the retrieved absorption coefficients of pollution aerosols was rather large (single scattering albedo of the order of 0.6–0.9 were observed in the month of April 2006), the corresponding low optical depths (~0.03 at 500 nm) are expected to limit the relevant radiative forcings. Still, the high specific forcing of this aerosol and its capability of altering snow surface albedo provide good reason for continuous monitoring.

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Simulation of trace gases and aerosols over the Indian domain: evaluation of the WRF-Chem model

Geoscientific Model Development Discussions ◽

10.5194/gmdd-7-431-2014 ◽

2014 ◽

Vol 7 (1) ◽

pp. 431-482 ◽

Cited By ~ 12

Author(s):

M. Michael ◽

A. Yadav ◽

S. N. Tripathi ◽

V. P. Kanawade ◽

A. Gaur ◽

...

Keyword(s):

Black Carbon ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Indian Subcontinent ◽

Monsoon Season ◽

Trace Gases ◽

Atmospheric Composition ◽

Vertical Profiles ◽

Monsoon Period ◽

Mixing Ratios

Abstract. The "online" meteorological and chemical transport Weather Research and Forecasting/Chemistry (WRF-Chem) model has been implemented over the Indian subcontinent for three consecutive summers in 2008, 2009 and 2010 to study the aerosol properties over the domain. The model simulated the meteorological parameters, trace gases and particulate matter. Predicted mixing ratios of trace gases (Ozone, carbon monoxide and sulfur dioxide) are compared with ground based observations over Kanpur. Simulated aerosol optical depth are compared with those observed at nine Aerosol Robotic Network stations (AERONET). The simulations show that the aerosol optical depth of the less polluted regions is better simulated compared to that of the locations where the aerosol loading is very high. The vertical profiles of extinction coefficient observed at the Kanpur Micropulse Lidar Network (MPLNET) station is underpredicted by the model by 10 to 50% for altitudes greater than 1.5 km and qualitatively simulate the elevated layers of aerosols. The simulated mass concentration of black carbon shows a correlation coefficient of 0.4 with observations. Vertical profiles of black carbon at various locations have also been compared with observations from an aircraft campaign held during pre-monsoon period of 2008 and 2009. This study shows that WRF-Chem model captures many important features of the observed atmospheric composition during the pre-monsoon season in India.

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Aerosol optical depth in the European Brewer Network

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-3885-2018 ◽

2018 ◽

Vol 18 (6) ◽

pp. 3885-3902 ◽

Cited By ~ 8

Author(s):

Javier López-Solano ◽

Alberto Redondas ◽

Thomas Carlund ◽

Juan J. Rodriguez-Franco ◽

Henri Diémoz ◽

...

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Input Data ◽

Scientific Interest ◽

Atmospheric Processes ◽

Ultraviolet Range ◽

Using Data ◽

Aerosol Properties ◽

Better Than

Abstract. Aerosols play an important role in key atmospheric processes and feature high spatial and temporal variabilities. This has motivated scientific interest in the development of networks capable of measuring aerosol properties over large geographical areas in near-real time. In this work we present and discuss results of an aerosol optical depth (AOD) algorithm applied to instruments of the European Brewer Network. This network is comprised of close to 50 Brewer spectrophotometers, mostly located in Europe and adjacent areas, although instruments operating at, for example, South America and Australia are also members. Although we only show results for instruments calibrated by the Regional Brewer Calibration Center for Europe, the implementation of the AOD algorithm described is intended to be used by the whole network in the future. Using data from the Brewer intercomparison campaigns in the years 2013 and 2015, and the period in between, plus comparisons with Cimel sun photometers and UVPFR instruments, we check the precision, stability, and uncertainty of the Brewer AOD in the ultraviolet range from 300 to 320 nm. Our results show a precision better than 0.01, an uncertainty of less than 0.05, and, for well-maintained instruments, a stability similar to that of the ozone measurements. We also discuss future improvements to our algorithm with respect to the input data, their processing, and the characterization of the Brewer instruments for the measurement of AOD.

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Sunphotometry of the 2006–2007 aerosol optical/radiative properties at the Himalayan Nepal Climate Observatory-Pyramid (5079 m a.s.l.)

Atmospheric Chemistry and Physics ◽

10.5194/acp-10-11209-2010 ◽

2010 ◽

Vol 10 (22) ◽

pp. 11209-11221 ◽

Cited By ~ 31

Author(s):

G. P. Gobbi ◽

F. Angelini ◽

P. Bonasoni ◽

G. P. Verza ◽

A. Marinoni ◽

...

Keyword(s):

High Altitude ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Radiative Forcing ◽

Monsoon Season ◽

Single Scattering ◽

Radiative Properties ◽

Mountain Range ◽

Anthropogenic Aerosol ◽

Aerosol Radiative

Abstract. In spite of being located at the heart of the highest mountain range in the world, the Himalayan Nepal Climate Observatory (5079 m a.s.l.) at the Ev-K2-CNR Pyramid is shown to be affected by the advection of pollution aerosols from the populated regions of southern Nepal and the Indo-Gangetic plains. Such an impact is observed along most of the period April 2006–March 2007 addressed here, with a minimum in the monsoon season. Backtrajectory-analysis indicates long-range transport episodes occurring in this year to originate mainly in the west Asian deserts. At this high altitude site, the measured aerosol optical depth is observed to be about one order of magnitude lower than the one measured at Ghandi College (60 m a.s.l.), in the Indo-Gangetic basin. As for Ghandi College, and in agreement with the in situ ground observations at the Pyramid, the fine mode aerosol optical depth maximizes during winter and minimizes in the monsoon season. Conversely, total optical depth maximizes during the monsoon due to the occurrence of elevated, coarse particle layers. Possible origins of these particles are wind erosion from the surrounding peaks and hydrated/cloud-processed aerosols. Assessment of the aerosol radiative forcing is then expected to be hampered by the presence of these high altitude particle layers, which impede an effective, continuous measurement of anthropogenic aerosol radiative properties from sky radiance inversions and/or ground measurements alone. Even though the retrieved absorption coefficients of pollution aerosols were rather large (single scattering albedo of the order of 0.6–0.9 were observed in the month of April 2006), the corresponding low optical depths (~0.03 at 500 nm) are expected to limit the relevant radiative forcing. Still, the high specific forcing of this aerosol and its capability of altering snow surface albedo provide good reasons for continuous monitoring.

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Space-Time Machine Learning Models to Analyze COVID-19 Pandemic Lockdown Effects on Aerosol Optical Depth over Europe

Remote Sensing ◽

10.3390/rs13153027 ◽

2021 ◽

Vol 13 (15) ◽

pp. 3027

Author(s):

Saleem Ibrahim ◽

Martin Landa ◽

Ondřej Pešek ◽

Karel Pavelka ◽

Lena Halounova

Keyword(s):

Machine Learning ◽

Air Quality ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Spatial Resolution ◽

Missing Values ◽

Space Time ◽

Spatial Coverage ◽

The Mean ◽

Prediction Approach

The recent COVID-19 pandemic affected various aspects of life. Several studies established the consequences of pandemic lockdown on air quality using satellite remote sensing. However, such studies have limitations, including low spatial resolution or incomplete spatial coverage. Therefore, in this paper, we propose a machine learning-based scheme to solve the pre-mentioned limitations by training an optimized space-time extra trees model for each year of the study period. The results have shown that our trained models reach a prediction accuracy up to 95% when predicting the missing values in the MODIS MCD19A2 Aerosol Optical Depth (AOD) product. The outcome of the mentioned scheme was a geo-harmonized atmospheric dataset for aerosol optical depth at 550 nm with 1 km spatial resolution and full coverage over Europe. As an application, we used the proposed machine learning based prediction approach in AOD levels analysis. We compared the mean AOD levels between the lockdown period from March to June in 2020 and the mean AOD values of the same period for the past 5 years. We found that AOD levels dropped over most European countries in 2020 but increased in several eastern and western countries. The Netherlands had the most significant average decrease in AOD levels (19%), while Spain had the highest average increase (10%). Moreover, we analyzed the relationship between the relative percentage difference of AOD and four meteorological variables. We found a positive correlation between AOD and relative humidity and a negative correlation between AOD and wind speed. The value of the proposed prediction scheme is further emphasized by taking into consideration that the reconstructed dataset can be used for future air quality studies concerning Europe.

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Analysis of Aerosol Optical Depth and Angstrom Exponents over an AERONET site at Pokhara, Nepal

BIBECHANA ◽

10.3126/bibechana.v18i1.29448 ◽

2021 ◽

Vol 18 (1) ◽

pp. 118-127

Author(s):

Jeevan Regmi ◽

Khem N Poudyal ◽

Amod Pokhrel ◽

Madhu Gyawali ◽

Anthony Barinelli ◽

...

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Monsoon Season ◽

Anthropogenic Aerosols ◽

Annual Average ◽

Average Value ◽

Monthly Average ◽

Aerosol Loading ◽

Post Monsoon ◽

Post Monsoon Season

The monthly variability of Aerosol Optical Depth at 0.50 μm (AOD0.50) and Ångström exponents (AE) based on spectral AODs over an Aerosol Robotic Network (AERONET) site Pokhara, are analyzed by using aerosol data of the year 2017. The AOD0.50 are characterized by low average values (0.21± 0.12) in monsoon, and highest values in pre-monsoon (0.67± 0.14) followed by winter (0.46± 0.28) and post-monsoon (0.33±.02) with an overall mean of 0.43 ± 0.02. The average AE obtained by using AODs at 0.44 μm and 0.87 μm is 1.20± 0.04 in pre-monsoon, 1.37± 0.05 in monsoon, 1.41±.01 in post-monsoon, and 1.37± 0.07 in winter with an annual average value of 1.35 ± 0.08. These overall variations of AE indicate that the majority of aerosol loading during the study period was mixture of fine and coarse mode aerosols and the influence of anthropogenic aerosols. The monthly average AOD suggests low aerosol loading in the months of the monsoon season (June to September) than other months of pre-monsoon season (March to May) and post-monsoon season (October and November). BIBECHANA 18 (2021) 118-127

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Spectral analysis of aerosol optical depth over aeronet sites of Nepal

BIBECHANA ◽

10.3126/bibechana.v17i0.26507 ◽

2020 ◽

Vol 17 ◽

pp. 80-88

Author(s):

Aashma Acharya ◽

Binod Adhikari ◽

Pratik Bhattarai ◽

Gopal Jha ◽

Shambhu Acharya ◽

...

Keyword(s):

Wavelet Analysis ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Suspended Particle ◽

Spatial And Temporal Variation ◽

Gangetic Plain ◽

Global Circulation ◽

Aerosol Loading ◽

Himalayan Foothills

The suspended particle aerosols especially anthropogenic are recognized to have degradation in the quality of the atmosphere and one of the factors to cause uncertainty in climate. In this paper, we have investigated the trend of the parameter ‘Aerosol Optical depth’ and by application of spectral based wavelet analysis; we extracted spatial and temporal variation over the selected AERONET sites of Nepal. We have taken the site Kyanjin_gompa, Lumbini, Pokhara and Kathmandu under the consideration of our study because of their geographical variability which is a significant factor for causing variation in local as well as global circulation of aerosols. As per data retrieved from Ground-Based remote sensing system for the year 2018 over the site Kyanjin gompa, Lumbini and Pokhara and for the year 2016 over the Kathmandu, we extracted the periodicity and frequency of the variation in AOD for each site by the application of continuous wavelet analysis on AOD at three different wavelengths. On reviewing the previous studies, it is seen that the area lying at the Indo-Gangetic plain exhibit high aerosol loading in comparison with the Himalayan foothills and central Himalayas of Nepal. We found not only the higher aerosol loading in atmosphere over site Lumbini but also higher periodicity. Likewise, we also found Pokhara as highly polluted as Lumbini. The investigation of data records over the site Kathmandu has shown increment in aerosol loading in the year 2016 compared with previous years. BIBECHANA 17 (2020) 80-88

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