Recent trends in aerosol optical properties derived from AERONET measurements

Abstract. The Aerosol Robotic Network (AERONET) has been providing high-quality retrievals of aerosol optical properties from the surface at worldwide locations for more than a decade. Many sites have continuous and consistent records for more than 10 years, which enables the investigation of long-term trends in aerosol properties at these locations. In this study, we present the results of a trend analysis at selected stations with long data records. In addition to commonly studied parameters such as aerosol optical depth (AOD) and Ångström exponent (AE), we also focus on inversion products including absorption aerosol optical depth (ABS), single-scattering albedo (SSA) and the absorption Ångström exponent (AAE). Level 2.0 quality assured data are the primary source. However, due to the scarcity of level 2.0 inversion products resulting from the strict AOD quality control threshold, we have also analyzed level 1.5 data, with some quality control screening to provide a reference for global results. Two statistical methods are used to detect and estimate the trend: the Mann–Kendall test associated with Sen's slope and linear least-squares fitting. The results of these statistical tests agree well in terms of the significance of the trend for the majority of the cases. The results indicate that Europe and North America experienced a uniform decrease in AOD, while significant (>90%) increases in these two parameters are found for North India and the Arabian Peninsula. The AE trends turn out to be different for North America and Europe, with increases for the former and decreases for the latter, suggesting opposite changes in fine/coarse-mode fraction. For level 2.0 inversion parameters, Beijing and Kanpur both experienced an increase in SSA. Beijing also shows a reduction in ABS, while the SSA increase for Kanpur is mainly due the increase in scattering aerosols. Increased absorption and reduced SSA are found at Solar_Village. At level 1.5, most European and North American sites also show positive SSA and negative ABS trends, although the data are more uncertain. The AAE trends are less spatially coherent due to large uncertainties, except for a robust increase at three sites in West Africa, which suggests a possible reduction in black carbon. Overall, the trends do not exhibit obvious seasonality for the majority of parameters and stations.

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Recent trends in aerosol optical properties derived from AERONET measurements

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-14351-2014 ◽

2014 ◽

Vol 14 (10) ◽

pp. 14351-14397 ◽

Cited By ~ 1

Author(s):

J. Li ◽

B. E. Carlson ◽

O. Dubovik ◽

A. A. Lacis

Keyword(s):

Optical Properties ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Kendall Test ◽

Single Scattering ◽

Least Square ◽

Aerosol Optical Properties ◽

Angstrom Exponent ◽

Ångström Exponent ◽

Ångstrom Exponent

Abstract. The Aerosol Robotic Network (AERONET) has been providing high-quality retrievals of aerosol optical properties from the surface at worldwide locations for more than a decade. Many sites have continuous and consistent records for more than 10 years, which enables the investigation of long-term trends of aerosol properties at these locations. In this study, we present trend analysis of AERONET data at 63 selected locations. In addition to commonly studied parameters such as Aerosol Optical Depth (AOD) and Ångström Exponent (AE), we also focus on Absorption Aerosol Optical Depth (ABS), Scattering Optical Depth (SCT), Single Scattering Albedo (SSA) and the Absorption Ångström Exponent (AAE). Two statistical methods are used to detect and estimate the trend: Mann–Kendall test associated with Sen's slope and linear least square fitting. Their results agree well in terms of the significance of the trend for the majority of the cases. The results indicate that Europe and North America experienced a uniform decrease in AOD and SCT, while significant (> 90%) increases of these two parameters are found for Kanpur, India. Most of European and North American sites also show negative trends for ABS, as well as three East Asian stations. The reduction in ABS results in positive SSA trends for these locations. The increase of SCT also leads to a positive SSA trend for Kanpur. Negative SSA trends are mostly found over South America, Australia and a few West European stations, which are mainly attributed to the increase of absorption. Fewer stations are found with significant trends for AE and AAE. In general, the trends do not exhibit obvious seasonality for the majority of the parameters and stations.

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Retrieval of aerosol single-scattering albedo and polarized phase function from polarized sun-photometer measurements for Zanjan's atmosphere

Atmospheric Measurement Techniques ◽

10.5194/amt-6-2659-2013 ◽

2013 ◽

Vol 6 (10) ◽

pp. 2659-2669 ◽

Cited By ~ 12

Author(s):

A. Bayat ◽

H. R. Khalesifard ◽

A. Masoumi

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Atmospheric Aerosols ◽

Phase Function ◽

Single Scattering ◽

Single Scattering Albedo ◽

Angstrom Exponent ◽

Ångström Exponent ◽

Sun Photometer ◽

Ångstrom Exponent

Abstract. The polarized phase function of atmospheric aerosols has been investigated for the atmosphere of Zanjan, a city in northwest Iran. To do this, aerosol optical depth, Ångström exponent, single-scattering albedo, and polarized phase function have been retrieved from the measurements of a Cimel CE 318-2 polarized sun-photometer from February 2010 to December 2012. The results show that the maximum value of aerosol polarized phase function as well as the polarized phase function retrieved for a specific scattering angle (i.e., 60°) are strongly correlated (R = 0.95 and 0.95, respectively) with the Ångström exponent. The latter has a meaningful variation with respect to the changes in the complex refractive index of the atmospheric aerosols. Furthermore the polarized phase function shows a moderate negative correlation with respect to the atmospheric aerosol optical depth and single-scattering albedo (R = −0.76 and −0.33, respectively). Therefore the polarized phase function can be regarded as a key parameter to characterize the atmospheric particles of the region – a populated city in the semi-arid area and surrounded by some dust sources of the Earth's dust belt.

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Aerosol optical properties at Lampedusa (Central Mediterranean). 1. Influence of transport and identification of different aerosol types

Atmospheric Chemistry and Physics ◽

10.5194/acp-6-697-2006 ◽

2006 ◽

Vol 6 (3) ◽

pp. 697-713 ◽

Cited By ~ 192

Author(s):

G. Pace ◽

A. di Sarra ◽

D. Meloni ◽

S. Piacentino ◽

P. Chamard

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Central Mediterranean ◽

Desert Dust ◽

Central Eastern Europe ◽

Angstrom Exponent ◽

The North ◽

Ångström Exponent ◽

Summer Maximum ◽

Ångstrom Exponent

Abstract. Aerosol optical depth and Ångström exponent were obtained from multi filter rotating shadowband radiometer (MFRSR) observations carried out at the island of Lampedusa, in the Central Mediterranean, in the period July 2001–September 2003. The average aerosol optical depth at 495.7 nm, τ, is 0.24±0.14; the average Ångström exponent, α, is 0.86±0.63. The observed values of τ range from 0.03 to 1.13, and the values of α vary from −0.32 to 2.05, indicating a large variability in aerosol content and size. In cloud-free conditions, 36% of the airmasses come from Africa, 25% from Central-Eastern Europe, and 19% from Western France, Spain and the North Atlantic. In summer, 42% of the airmasses is of African origin. In almost all cases African aerosols display high values of τ and low values of α, typical of Saharan dust (average values of τ and α are 0.36 and 0.42, respectively). Particles originating from Central-Eastern Europe show relatively large average values of τ and α (0.23 and 1.5, respectively), while particles from Western France, Spain and the North Atlantic show the lowest average values of τ (0.15), and relatively small values of α (0.92). Intermediate values of α are often connected with relatively fast changes of the airmass originating sector, suggesting the contemporary presence of different types of particles in the air column. Clean marine conditions are rare at Lampedusa, and are generally associated with subsidence of the airmasses reaching the island. Average values of τ and α for clean marine conditions are 0.11 and 0.86, respectively. The largest values of α (about 2) were observed in August 2003, when large scale forest fires in Southern Europe produced consistent amounts of fine combustion particles, that were transported to the Central Mediterranean by a persistent high pressure system over Central Europe. Smoke particles in some cases mix with desert dust, producing intermediate values of α. The seasonal distribution of the meteorological patterns over the Mediterranean, the efficiency of the aerosol production mechanisms, and the variability of the particles' residence time produce a distinct seasonal cycle of aerosol optical depths and Ångström exponent values. Particles originating from all sectors show a summer maximum in aerosol optical depth. The summer increase in optical depth for European aerosols is linked with an increment in the values of α, that indicates an enhancement in the number of fine particles. The summer maximum of τ for African particles is associated with a weak reduction in the Ångström exponent, suggesting an increase in the total number of particles and a relatively more intense transport of large particles. The observations were classified according to the aerosol optical properties, and two main classes have been identified: desert dust and biomass burning/urban-industrial aerosols. Values of τ and α averaged over the whole observing period are 0.37 and 0.15 for desert dust, and 0.27 and 1.77 for urban-industrial/biomass burning aerosols.

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Measurements of optical properties of atmospheric aerosols in Northern Finland

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-5-11703-2005 ◽

2005 ◽

Vol 5 (6) ◽

pp. 11703-11728 ◽

Cited By ~ 1

Author(s):

V. Aaltonen ◽

H. Lihavainen ◽

V.-M. Kerminen ◽

M. Komppula ◽

J. Hatakka ◽

...

Keyword(s):

Optical Properties ◽

Size Distribution ◽

Seasonal Pattern ◽

Late Summer ◽

Aerosol Optical Properties ◽

Air Masses ◽

Angstrom Exponent ◽

Northern Border ◽

Ångström Exponent ◽

Ångstrom Exponent

Abstract. Three years of continuous measurements of aerosol optical properties and simultaneous aerosol number size distribution measurements at Pallas GAW station, a remote subarctic site in the northern border of the boreal forest zone, have been analysed. The scattering coefficient at 550 nm varied from 0.2 to 94.4 Mm−1 with an average of 7.1±8.6 Mm−1. Both the scattering and backscattering coefficients had a clear seasonal cycle with an autumn minimum and a 4–5 times higher summer maximum. The scattering was dominated by submicron aerosols and especially so during late summer and autumn. The Ångström exponent had a clear seasonal pattern with maximum values in late summer and minimum values during wintertime. The highest hemispheric backscattering fraction values were observed in autumn, indicating clean air with few scattering particles and a particle size distribution strongly dominated by ultrafine particles. To analyse the influence of air mass origin on the aerosol optical properties a trajectory climatology was applied to the Pallas aerosol data. The most polluted trajectory patterns represented air masses from the Kola Peninsula, Scandinavia and Russia as well as long-range transport from Britain and Eastern Europe. These air masses had the largest average scattering and backscattering coefficients for all seasons. Higher than average values of the Ångström exponent were also observed in connection with transport from these areas.

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The regime of Aerosol Optical Depth and Ångström exponent over Central and South Asia

E3S Web of Conferences ◽

10.1051/e3sconf/20199901003 ◽

2019 ◽

Vol 99 ◽

pp. 01003

Author(s):

Athina Avgousta Floutsi ◽

Marios Bruno Korras Carraca ◽

Christos Matsoukas ◽

Nikos Hatzianastassiou ◽

George Biskos

Keyword(s):

South Asia ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Atmospheric Aerosols ◽

Dust Particles ◽

Desert Dust ◽

Angstrom Exponent ◽

Ångström Exponent ◽

Dust Load ◽

Ångstrom Exponent

Central and South Asia are regions of particular interest for studying atmospheric aerosols, being among the largest sources of desert dust aerosols globally. In this study we use the newest collection (C061) of MODIS - Aqua aerosol optical depth (AOD) at 550 nm and Ångström exponent (a) at 412/470 nm over the 15-year period between 2002 and 2017, providing the longest analyzed dataset for this region. According to our results, during spring and summer, high aerosol load (AOD up to 1.2) consisting of coarse desert dust particles, as indicated by a values as low as 0.15, is observed over the Taklamakan, Thar and Registan deserts and the region between the Aral and Caspian seas. The dust load is much lower during winter and autumn (lower AOD and higher a values compared to the other seasons). The interannual variation of AOD and a suggests that the dust load exhibits large decreasing trends (AOD slopes down to -0.22, a slopes up to 0.47 decade-1) over the Thar desert and large increasing trends between the Aral and Caspian seas (AOD and a slopes up to 0.23 decade-1 and down to -0.61 decade-1, respectively.) The AOD data are evaluated against AERONET surface-based measurements. Generally, MODIS and AERONET data are in good agreement with a correlation coefficient (R) equal to 0.835.

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Estimating cloud condensation nuclei number concentrations using aerosol optical properties: role of particle number size distribution and parameterization

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-15483-2019 ◽

2019 ◽

Vol 19 (24) ◽

pp. 15483-15502 ◽

Cited By ~ 1

Author(s):

Yicheng Shen ◽

Aki Virkkula ◽

Aijun Ding ◽

Krista Luoma ◽

Helmi Keskinen ◽

...

Keyword(s):

Optical Properties ◽

Size Distribution ◽

Cloud Condensation Nuclei ◽

Size Distributions ◽

Condensation Nuclei ◽

Aerosol Optical Properties ◽

Average Bias ◽

Angstrom Exponent ◽

Ångström Exponent ◽

Ångstrom Exponent

Abstract. The concentration of cloud condensation nuclei (CCN) is an essential parameter affecting aerosol–cloud interactions within warm clouds. Long-term CCN number concentration (NCCN) data are scarce; there are a lot more data on aerosol optical properties (AOPs). It is therefore valuable to derive parameterizations for estimating NCCN from AOP measurements. Such parameterizations have already been made, and in the present work a new parameterization is presented. The relationships between NCCN, AOPs, and size distributions were investigated based on in situ measurement data from six stations in very different environments around the world. The relationships were used for deriving a parameterization that depends on the scattering Ångström exponent (SAE), backscatter fraction (BSF), and total scattering coefficient (σsp) of PM10 particles. The analysis first showed that the dependence of NCCN on supersaturation (SS) can be described by a logarithmic fit in the range SS <1.1 %, without any theoretical reasoning. The relationship between NCCN and AOPs was parameterized as NCCN≈((286±46)SAE ln(SS/(0.093±0.006))(BSF − BSFmin) + (5.2±3.3))σsp, where BSFmin is the minimum BSF, in practice the 1st percentile of BSF data at a site to be analyzed. At the lowest supersaturations of each site (SS ≈0.1 %), the average bias, defined as the ratio of the AOP-derived and measured NCCN, varied from ∼0.7 to ∼1.9 at most sites except at a Himalayan site where the bias was >4. At SS >0.4 % the average bias ranged from ∼0.7 to ∼1.3 at most sites. For the marine-aerosol-dominated site Ascension Island the bias was higher, ∼1.4–1.9. In other words, at SS >0.4 % NCCN was estimated with an average uncertainty of approximately 30 % by using nephelometer data. The biases were mainly due to the biases in the parameterization related to the scattering Ångström exponent (SAE). The squared correlation coefficients between the AOP-derived and measured NCCN varied from ∼0.5 to ∼0.8. To study the physical explanation of the relationships between NCCN and AOPs, lognormal unimodal particle size distributions were generated and NCCN and AOPs were calculated. The simulation showed that the relationships of NCCN and AOPs are affected by the geometric mean diameter and width of the size distribution and the activation diameter. The relationships of NCCN and AOPs were similar to those of the observed ones.

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Detection of Saharan dust and biomass burning events using near real-time intensive aerosol optical properties in the northwestern Mediterranean

10.5194/acp-2015-902 ◽

2016 ◽

Author(s):

M. Ealo ◽

A. Alastuey ◽

A. Ripoll ◽

N. Pérez ◽

M. C. Minguillón ◽

...

Keyword(s):

Optical Properties ◽

Biomass Burning ◽

Mineral Dust ◽

Organic Aerosol ◽

Saharan Dust ◽

Aerosol Optical Properties ◽

Angstrom Exponent ◽

Ångström Exponent ◽

Dust Events ◽

Ångstrom Exponent

Abstract. The study of Saharan dust events (SDE) and biomass burning (BB) emissions are both topic of great scientific interest since they are frequent and important polluting scenarios affecting air quality and climate. The main aim of this work is evaluating the feasibility of using near real-time in situ aerosol optical measurements for the detection of these atmospheric events in the Western Mediterranean Basin (WMB). With this aim, intensive aerosol optical properties (SAE: scattering Ångström exponent, AAE: absorption Ångström exponent, SSAAE: single scattering albedo Ångström exponent, and g: asymmetry parameter) were derived from multi-wavelength aerosol light scattering, hemispheric backscattering and absorption measurements performed at regional (Montseny; MSY, 720 m a.s.l.) and continental (Montsec; MSA, 1570 m a.s.l.) background sites in the WMB. A sensitivity study aiming at calibrating the measured intensive optical properties for SDE and BB detection is presented and discussed. The detection of Saharan dust events (SDE) by means of the SSAAE parameter and Ångström matrix depended on the altitude of the measurement station, and on SDE intensity. At MSA (mountain-top site) SSAAE detected around 85% of SDE compared with 50% at MSY station, where pollution episodes dominated by fine anthropogenic particles frequently masked the effect of mineral dust on optical properties during less intense SDE. Furthermore, an interesting feature of SSAAE was its capability to detect the presence of mineral dust after the end of SDE. Thus, resuspension processes driven by summer regional atmospheric circulations and dry conditions after SDE favored the accumulation of mineral dust at regional level having important consequences for air quality. On average, SAE, AAE and g ranged between -0.7 and 1, 1.3 and 2.5, and 0.5 and 0.75, respectively, during SDE. Based on the Aethalometer model, biomass burning (BB) contribution to equivalent black carbon (BC) accounted for 36% and 40% at MSY and MSA respectively. Linear relationships were found between AAE and %BCbb, with AAE values reaching around 1.5 when %BCbb was higher than 50%. BB contribution to organic matter (OM) at MSY was around 30%. Thus FF combustion sources showed important contributions to both BC and OM in the region under study. Results for OM source apportionment showed good agreement with simultaneous biomass burning organic aerosol (BBOA) and hydrocarbon-like organic aerosol (HOA) calculated from Positive Matrix Factorization (PMF) applied to simultaneous Aerosol Mass Spectrometer (ACSM) measurements. A wildfire episode was identified at MSY, showing AAE values up to 2 when daily BB contributions to BC and OM were 73% and 78% respectively.

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Studying Air Pollutants Origin and Associated Meteorological Parameters over Seoul from 2000 to 2009

Advances in Meteorology ◽

10.1155/2015/704178 ◽

2015 ◽

Vol 2015 ◽

pp. 1-12 ◽

Cited By ~ 6

Author(s):

Sunmin Park ◽

Hesham El-Askary ◽

Ismail Sabbah ◽

Hanbin Kwak ◽

Anup K. Prasad ◽

...

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Air Pollutants ◽

Winter Season ◽

Summer Season ◽

Seasonal Effect ◽

Temporal Characteristics ◽

Angstrom Exponent ◽

Ångström Exponent ◽

Ångstrom Exponent

We investigate the temporal characteristics of major air pollutants collected from 44 air quality stations over the city of Seoul, Korea, namely, nitrogen dioxide, carbon monoxide, particular matter at 10 microns, and sulfur dioxide (SO2) between 2000 and 2009. The corresponding satellite datasets, namely, aerosol optical depth (AODsat), Ångström exponent, and fine mode fraction, collected from moderate resolution imaging spectroradiometer (MODIS) as well as the Aeronet ground aerosol optical depth (AODaeronet), have been analyzed. Pollutants’ seasonal effect has been inferred from the precipitation and temperature. The four pollutants under study show varying temporal characteristics with different annual mean concentration patterns. The monthly mean of mentioned pollutants all show similar low concentrations during the summer season and high concentrations during the winter season. We found that pollution is strongly linked to temperature and precipitation variability, especially during the fall season. Satellite data analysis provides information on the pollutants origin whether of natural or anthropogenic type. Our results indicate that the anthropogenic aerosol is dominant in the summer season even though the concentration was lower than the other seasons. AODaeronetand Ångström exponent indicated high positive and negative correlation coefficients with PM10, 0.60, and −0.45, respectively. Both small and large sizes of aerosols existed in 2007; however coarse size of aerosols was the primary component in 2002.

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Extreme Saharan dust event over the southern Iberian Peninsula in september 2007: active and passive remote sensing from surface and satellite

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-15673-2009 ◽

2009 ◽

Vol 9 (4) ◽

pp. 15673-15723

Author(s):

J. L. Guerrero-Rascado ◽

F. J. Olmo ◽

I. Avilés-Rodríguez ◽

F. Navas-Guzmán ◽

D. Pérez-Ramírez ◽

...

Keyword(s):

Remote Sensing ◽

Iberian Peninsula ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Saharan Dust ◽

Dust Event ◽

Passive Remote Sensing ◽

Angstrom Exponent ◽

Ångström Exponent ◽

Ångstrom Exponent

Abstract. This study investigates aerosol optical properties during the extreme Saharan dust event detected from 3 to 7 September 2007 over Granada, southern Iberian Peninsula, with both active and passive remote sensing instrumentation from surface and satellite. The intensity of the event was visualized on the aerosol optical depth series obtained by the sun-photometer Cimel CE 318-4 operated at Granada in the framework of AERONET from August 2004 until December 2008 (level 2 data). A combination of large aerosol optical depth (0.86–1.50) at 500 nm, and reduced Angström exponent (0.1–0.25) in the range 440–870 nm, was detected on 6 September during daytime. This Saharan dust event also affected other Iberian Peninsula stations included in AERONET (El Arenosillo and Évora stations). During the most intense stage, on 6 September, maximum aerosol backscatter values were a factor of 8 higher than other maxima during this Saharan dust event. Values up to 1.5×10−2 km−1 sr−1 at 355 and 532 nm were detected in the layer with the greatest aerosol load between 3–4 km a.s.l., although aerosol particles were also detected up to 5.5 km a.s.l. In this stage of the event, dust particles at these altitudes showed a backscatter-related Angström exponent between −0.44 and 0.53 for the two spectral intervals considered. The results from different measurements (active/passive and ground-based/satellite) reveal the importance of performing multi-instrumental measurements to properly characterize the contribution of different aerosol types from different sources during extreme events.

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