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

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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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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A new multispectral photometer for monitoring aerosol microphysical, optical, and radiative properties

10.5194/amt-2021-365 ◽

2021 ◽

Author(s):

Yu Zheng ◽

Huizheng Che ◽

Yupeng Wang ◽

Xiangao Xia ◽

Xiuqing Hu ◽

...

Keyword(s):

Water Vapor ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Radiative Forcing ◽

Integrated Design ◽

Single Scattering ◽

Radiative Properties ◽

Mean Values ◽

Smart Control ◽

Fine Mode

Abstract. A new multispectral photometer, named CW193, was proposed in this study for monitoring aerosol microphysical, optical, and radiative properties. The instrument has a highly integrated design, smart control performance, and is composed of three parts (an optical head, a robotic drive platform, and a stents system). Because of its low maintenance requirements, this instrument is appropriate for the deployment in remote and unpopulated regions. Based on the synchronous measurements, the CW193 products was validated using reference data from the AERONET CE318 photometer. The results show that the raw digital counts from CW193 agree well the counts from AERONET (R2 > 0.97), with daily average triplets of around 1.2 % to 3.0 % for the ultraviolet band and less than 2.0 % for the visible and infrared bands. A good aerosol optical depth agreement (R > 0.99, 100 % within expected error) and root mean square error (RMSE) values ranging from 0.006 (for the 870 nm band) to 0.016 (for 440 nm the band) are obtained, with a relative mean bias (RMB) ranging from 0.922 to 1.112 and an aerosol optical depth bias within ±0.04. The maximum deviations for fine-mode particles varied from about 8.9 % to 77.6 %, whereas the variation for coarse-mode particles was about 13.1 % to 29.1 %. The deviation variations of the single scattering albedo were approximately 0.1–1.8 %, 0.6–1.9 %, 0.1–2.6 %, and 0.8–3.5 % for the 440 nm, 675 nm, 870 nm, and 1020 nm bands, respectively. For the aerosol direct radiative forcing, deviations of approximately 4.8–12.3 % was obtained at the Earth’s surface and 5.4–15.9 % for the top of the atmosphere. In addition, the water vapor retrievals showed a satisfactory accuracy, characterized by a high R value (~0.997), a small RMSE (~0.020), and good expected error distribution (100 % within expected error). The water vapor RMB was about 0.979 and the biases mostly varied within ±0.04, whereas the mean values were concentrated within ±0.02.

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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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Dust optical properties over North Africa and Arabian Peninsula derived from the AERONET dataset

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-11-20181-2011 ◽

2011 ◽

Vol 11 (7) ◽

pp. 20181-20201 ◽

Cited By ~ 7

Author(s):

D. Kim ◽

M. Chin ◽

H. Yu ◽

T. F. Eck ◽

A. Sinyuk ◽

...

Keyword(s):

Refractive Index ◽

Optical Properties ◽

Aerosol Optical Depth ◽

Optical Depth ◽

North Africa ◽

Radiative Forcing ◽

Arabian Peninsula ◽

Single Scattering ◽

Major Fraction ◽

Remote Sensing Techniques

Abstract. Dust optical properties over North Africa and the Arabian Peninsula are extracted from the quality assured multi-year datasets obtained at 14 sites of the Aerosol Robotic Network (AERONET). We select the data with (a) large aerosol optical depth (AOD ≥ 0.4 at 440 nm) and (b) small Ångström exponent (Åext ≤ 0.2) for retaining high accuracy and reducing interference of non-dust aerosols. The result indicates that the major fraction of high aerosol optical depth days are dominated by dust over these sites even though it varies depending on location and time. We have found that the annual mean and standard deviation of single scattering albedo, asymmetry parameter, real refractive index, and imaginary refractive index for Saharan and Arabian desert dust is 0.946 ± 0.005, 0.752 ± 0.014, 1.498 ± 0.032, and 0.0025 ± 0.0036 at 550 nm wavelength, respectively. Dust aerosol selected by this method is less absorbing than the previously reported values over these sites. The weaker absorption of dust from this study is consistent with the previously studies using remote sensing techniques. These results can help to constrain uncertainties in estimating global dust shortwave radiative forcing.

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Dust optical properties over North Africa and Arabian Peninsula derived from the AERONET dataset

Atmospheric Chemistry and Physics ◽

10.5194/acp-11-10733-2011 ◽

2011 ◽

Vol 11 (20) ◽

pp. 10733-10741 ◽

Cited By ~ 86

Author(s):

D. Kim ◽

M. Chin ◽

H. Yu ◽

T. F. Eck ◽

A. Sinyuk ◽

...

Keyword(s):

Refractive Index ◽

Optical Properties ◽

Aerosol Optical Depth ◽

Optical Depth ◽

North Africa ◽

Radiative Forcing ◽

Arabian Peninsula ◽

Single Scattering ◽

Major Fraction ◽

Remote Sensing Techniques

Abstract. Dust optical properties over North Africa and the Arabian Peninsula are extracted from the quality assured multi-year datasets obtained at 14 sites of the Aerosol Robotic Network (AERONET). We select the data with (a) large aerosol optical depth (AOD ≥ 0.4 at 440 nm) and (b) small Ångström exponent (Åext ≤ 0.2) for retaining high accuracy and reducing interference of non-dust aerosols. The result indicates that the major fraction of high aerosol optical depth days are dominated by dust over these sites even though it varies depending on location and time. We have found that the annual mean and standard deviation of single scattering albedo, asymmetry parameter, real refractive index, and imaginary refractive index for Saharan and Arabian desert dust is 0.944 ± 0.005, 0.752 ± 0.014, 1.498 ± 0.032, and 0.0024 ± 0.0034 at 550 nm wavelength, respectively. Dust aerosol selected by this method is less absorbing than the previously reported values over these sites. The weaker absorption of dust from this study is consistent with the studies using remote sensing techniques from satellite. These results can help to constrain uncertainties in estimating global dust shortwave radiative forcing.

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A Method to Estimate Aerosol Radiative Forcing from Spectral Optical Depths

Journal of the Atmospheric Sciences ◽

10.1175/jas3663.1 ◽

2006 ◽

Vol 63 (3) ◽

pp. 1082-1092 ◽

Cited By ~ 30

Author(s):

S. K. Satheesh ◽

J. Srinivasan

Keyword(s):

Chemical Composition ◽

Optical Depth ◽

Radiative Forcing ◽

Field Experiments ◽

Single Scattering ◽

Single Scattering Albedo ◽

Radiative Properties ◽

Aerosol Radiative Forcing ◽

Sky Radiance ◽

Aerosol Radiative

Abstract Radiative forcing of aerosols is much more difficult to estimate than that of well-mixed gases due to the large spatial variability of aerosols and the lack of an adequate database on their radiative properties. Estimation of aerosol radiative forcing generally requires knowledge of its chemical composition, which is sparse. Ground-based sky radiance measurements [e.g., aerosol robotic network (AERONET)] can provide key parameters such as the single-scattering albedo, but in shipborne experiments over the ocean it is difficult to make sky radiance measurements and hence these experiments cannot provide parameters such as the single-scattering albedo. However, aerosol spectral optical depth data (cruise based as well as satellite retrieved) are available quite extensively over the ocean. Spectral optical depth measurements have been available since the 1970s, and spectral turbidity measurements (carried out at meteorological departments all over the world) have been available for several decades, while long-term continuous chemical composition information is not available. A new method to differentiate between scattering and absorbing aerosols is proposed here. This can be used to derive simple aerosol models that are optically equivalent and can simulate the observed aerosol optical properties and radiative fluxes, from spectral optical depth measurements. Thus, aerosol single-scattering albedo and, hence, aerosol radiative forcing can be estimated. Note that the proposed method is to estimate clear-sky aerosol radiative forcing (over regions where chemical composition data or sky radiance data are not available) and not to infer its exact chemical composition. Using several independent datasets from field experiments, it is demonstrated that the proposed method can be used to estimate aerosol radiative forcing (from spectral optical depths) with an accuracy of ±2 W m−2.

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Retrieval of aerosol single scattering albedo using joint satellite and surface visibility measurements

10.5194/egusphere-egu2020-11075 ◽

2020 ◽

Author(s):

Jing Li ◽

Yueming Dong

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Radiative Forcing ◽

Optical Parameter ◽

Single Scattering ◽

Single Scattering Albedo ◽

Retrieval Algorithm ◽

Extensive Coverage ◽

Satellite Sensors ◽

Aerosol Radiative

Aerosol single scattering albedo is a critical optical parameter that determines aerosol radiative effect. However, most existing passive satellite sensors such as MODIS and VIIRS only measures the intensity of reflected solar radiation and can only retrieve aerosol optical depth, while aerosol single scattering albedo needs to be assumed in the retrieval algorithm. On the other hand, if aerosol optical depth is known, it would be possible to retrieve aerosol single scattering albedo using satellite sensors. &#160;In this study, we develop a machine learning based algorithm that retrieves aerosol single scattering albedo using joint visibility and satellite measurements. Combined with meteorology variables including relative humidity and boundary layer height, surface visibility can be converted to column aerosol optical depth. Then combining this converted aerosol optical depth with VIIRS measured TOA apparent reflectance, we retrieve aerosol single scattering albedo at over 2000 stations worldwide. The results compare well with AERONET retrieved SSA. However, compared with AERONET, visibility is recorded at every WMO meteorology station and has much more extensive coverage. We also applied our method to surface PM2.5 measurements obtained satisfactory results. Our work provides an aerosol single scattering albedo dataset with extensive coverage over land, which can be used for aerosol radiative forcing calculations and model validation.

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Aerosol optical, microphysical and radiative properties at regional background insular sites in the western Mediterranean

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-12177-2016 ◽

2016 ◽

Vol 16 (18) ◽

pp. 12177-12203 ◽

Cited By ~ 21

Author(s):

Michaël Sicard ◽

Rubén Barragan ◽

François Dulac ◽

Lucas Alados-Arboledas ◽

Marc Mallet

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Forest Fires ◽

Urban Areas ◽

Radiative Forcing ◽

Mediterranean Basin ◽

Western Mediterranean ◽

Radiative Properties ◽

Regional Background ◽

Western Mediterranean Basin

Abstract. In the framework of the ChArMEx (the Chemistry-Aerosol Mediterranean Experiment; http://charmex.lsce.ipsl.fr/) program, the seasonal variability of the aerosol optical, microphysical and radiative properties derived from AERONET (Aerosol Robotic Network; http://aeronet.gsfc.nasa.gov/) is examined in two regional background insular sites in the western Mediterranean Basin: Ersa (Corsica Island, France) and Palma de Mallorca (Mallorca Island, Spain). A third site, Alborán (Alborán Island, Spain), with only a few months of data is considered for examining possible northeast–southwest (NE–SW) gradients of the aforementioned aerosol properties. The AERONET dataset is exclusively composed of level 2.0 inversion products available during the 5-year period 2011–2015. AERONET solar radiative fluxes are compared with ground- and satellite-based flux measurements. To the best of our knowledge this is the first time that AERONET fluxes are compared with measurements at the top of the atmosphere. Strong events (with an aerosol optical depth at 440 nm greater than 0.4) of long-range transport aerosols, one of the main drivers of the observed annual cycles and NE–SW gradients, are (1) mineral dust outbreaks predominant in spring and summer in the north and in summer in the south and (2) European pollution episodes predominant in autumn. A NE–SW gradient exists in the western Mediterranean Basin for the aerosol optical depth and especially its coarse-mode fraction, which all together produces a similar gradient for the aerosol direct radiative forcing. The aerosol fine mode is rather homogeneously distributed. Absorption properties are quite variable because of the many and different sources of anthropogenic particles in and around the western Mediterranean Basin: North African and European urban areas, the Iberian and Italian peninsulas, most forest fires and ship emissions. As a result, the aerosol direct forcing efficiency, more dependent to absorption than the absolute forcing, has no marked gradient.

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Aerosol optical properties of size segregated aerosol particles and radiative forcing over Pokhara valley

Himalayan Physics ◽

10.3126/hp.v8i0.29939 ◽

2019 ◽

Vol 8 ◽

pp. 1-10

Author(s):

Jeevn Regmi ◽

Khem N Poudyal ◽

Amod Pokhrel ◽

Anthony Barinelli ◽

Rudra Aryal

Keyword(s):

Optical Properties ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Radiative Forcing ◽

Monsoon Season ◽

Aerosol Particles ◽

Aerosol Optical Properties ◽

Maximum Value ◽

Fine Mode ◽

Pokhara Valley

The AERONET data from sun/sky radiometer over Pokhara (2017) was analyzed to observe aerosol optical depth (AOD) of size segregated particles and radiative forcing. Fine mode particles have over seventy percent of contribution to AOD in all months with the maximum, ninety-four percent, on November and February, and minimum on July, seventy-nine percent. The monthly mean top of atmosphere (TOA) forcing are negative −23.225 ± 4.71 Wm−2 in March, −28.958 ± 4.71 Wm−2 in April and −19.616 ± 4.71 Wm−2 in May. The negative value of TOA during all the months in pre-monsoon season indicates net cooling. Whereas surface forcing (BOA forcing) was found to be positive with a maximum value of 111.18 ± 27.63 Wm−2 during April and a minimum of 56.22 ± 27.63 Wm−2 during May. The resultant atmospheric forcing is the absorption due to aerosols within the atmosphere and found to be +267.57 Wm−2 during April and +228.55 Wm−2 during May; indicating significant heating of the atmosphere.

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Aerosol Optical Depth Measurements at high altitude and polar WMO Global Atmospheric Watch - PFR Network Stations

10.5194/egusphere-egu2020-6161 ◽

2020 ◽

Author(s):

Stelios Kazadzis ◽

Natalia Kouremeti ◽

Julian Groebner

Keyword(s):

High Altitude ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Radiative Forcing ◽

Global Climate ◽

Climate Variable ◽

Aerosol Radiative Forcing ◽

Mauna Loa ◽

Filter Radiometer

Multiwavelength aerosol optical depth (AOD) has been defined as an essential climate variable for the Global Climate Observing System (GCOS) and the Global Atmosphere Watch (GAW) Program of the World Meteorological Organization. It is the most important parameter related to aerosol radiative forcing studies. PMOD/WRC have developed the Precision Filter Radiometer (PFR) that has been used for long term AOD measurements under a GAW-PFR Network of sun-photometers started in 1995 at Davos Switzerland and from 1999 at other locations, worldwide.Here we present:An overview of the results of the long term GAW-PFR AOD series for four high altitude stations (Izana/Spain, Mauna Loa/USA, Mt. Walliguan/China and Jungfraujoch/Switzerland). Mean AODs at 500nm were from 0.015 up to 0.096 with small negative changes per year for all stations.An overview of the results for polar stations (Ny &#197;lesund/Norway, Summit/Denmark, Marambio/Finland). Ny &#197;lesund mean AODs at 500nm were almost double compared with the other stations.

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