scholarly journals Estimation of aerosol complex refractive indices for both fine and coarse modes simultaneously based on AERONET remote sensing products

2017 ◽  
Vol 10 (9) ◽  
pp. 3203-3213 ◽  
Author(s):  
Ying Zhang ◽  
Zhengqiang Li ◽  
Yuhuan Zhang ◽  
Donghui Li ◽  
Lili Qie ◽  
...  
Keyword(s):  
Imaginary Part ◽  
Atmospheric Aerosols ◽  
Fine Particles ◽  
Winter Season ◽  
Water Soluble ◽  
Refractive Indices ◽  
Coarse Mode ◽  
Seasonal Characteristics ◽  
Climate Change Assessment ◽  
Log Normal

Abstract. Climate change assessment, especially model evaluation, requires a better understanding of complex refractive indices (CRIs) of atmospheric aerosols – separately for both fine and coarse modes. However, the widely used aerosol CRI obtained by the global Aerosol Robotic Network (AERONET) corresponds to total-column aerosol particles without separation for fine and coarse modes. This paper establishes a method to separate CRIs of fine and coarse particles based on AERONET volume particle size distribution (VPSD), aerosol optical depth (AOD) and absorbing AOD (AAOD). The method consists of two steps. First a multimodal log-normal distribution that best approximates the AERONET VPSD is found. Then the fine and coarse mode CRIs are found by iterative fitting of AERONET AODs to Mie calculations. The numerical experiment shows good performance for typical water-soluble, biomass burning and dust aerosol types, and the estimated uncertainties on the retrieved sub-mode CRIs are about 0.11 (real part) and 78 % (imaginary part). The 1-year measurements at the AERONET Beijing site are processed, and we obtain CRIs of 1.48–0.010i (imaginary part at 440 nm is 0.012) for fine mode particles and 1.49–0.004i (imaginary part at 440 nm is 0.007) for coarse mode particles, for the period of 2014–2015. Our results also suggest that both fine and coarse aerosol mode CRIs have distinct seasonal characteristics; in particular, CRIs of fine particles in winter season are significantly higher than summer due to possible anthropogenic influences.

scholarly journals Estimation of aerosol complex refractive indices for both fine and coarse modes simultaneously based on AERONET remote sensing products

2017 ◽  
Author(s):  
Ying Zhang ◽  
Zhengqiang Li ◽  
Yuhuan Zhang ◽  
Donghui Li ◽  
Lili Qie ◽  
...  
Keyword(s):  
Imaginary Part ◽  
Atmospheric Aerosols ◽  
Fine Particles ◽  
Winter Season ◽  
Water Soluble ◽  
Refractive Indices ◽  
Coarse Mode ◽  
Seasonal Characteristics ◽  
Climate Change Assessment ◽  
One Year

Abstract. Climate change assessment, especially model evaluation, needs to know complex refractive indices (CRI) of atmospheric aerosols, separately for both fine and coarse modes. However, the widely used aerosol CRI obtained by the global Aerosol Robotic Network (AERONET), correspond to total-column aerosol particles without separation for fine and coarse modes. This paper establishes a method to separate CRIs of fine and coarse particles based on AERONET aerosol products, including volume particle size distribution (VPSD), aerosol optical depth (AOD) and absorbing AOD. The method consists of VPSD breaking-down and sub-mode CRI separation parts and yields spectral CRIs for both fine and coarse modes simultaneously. Numerical experiment shows good performance for typical water-soluble, biomass burning and dust aerosol types and the estimated uncertainties on the retrieved sub-mode CRIs are about 0.11 (real part) and 78 % (imaginary part), respectively. One year measurements at AERONET Beijing site are processed and we obtain CRIs of 1.48-0.010i (imaginary part at 440 nm is 0.012) for fine mode particles and 1.49-0.004i (imaginary part at 440 nm is 0.007) for coarse mode particles, for the period of 2014–2015. Our results also suggest that both aerosol fine and coarse mode CRIs have distinct seasonal characteristics, particularly CRIs of fine particles in winter season are significantly higher than summer, due to possible anthropogenic influences.

scholarly journals Advanced characterisation of aerosol size properties from measurements of spectral optical depth using the GRASP algorithm

2017 ◽  
Vol 10 (10) ◽  
pp. 3743-3781 ◽  
Author(s):  
Benjamin Torres ◽  
Oleg Dubovik ◽  
David Fuertes ◽  
Gregory Schuster ◽  
Victoria Eugenia Cachorro ◽  
...  
Keyword(s):  
Optical Depth ◽  
Atmospheric Aerosols ◽  
Volume Concentration ◽  
A Priori ◽  
Western Mediterranean ◽  
Dominant Mode ◽  
Coarse Mode ◽  
Fine Mode ◽  
The Difference ◽  
Log Normal

Abstract. This study evaluates the potential of using aerosol optical depth (τa) measurements to characterise the microphysical and optical properties of atmospheric aerosols. With this aim, we used the recently developed GRASP (Generalized Retrieval of Aerosol and Surface Properties) code for numerical testing of six different aerosol models with different aerosol loads. The direct numerical simulations (self-consistency tests) indicate that the GRASP-AOD retrieval provides modal aerosol optical depths (fine and coarse) to within 0.01 of the input values. The retrieval of the fine-mode radius, width and volume concentration are stable and precise if the real part of the refractive index is known. The coarse-mode properties are less accurate, but they are significantly improved when additional a priori information is available. The tests with random simulated errors show that the uncertainty in the bimodal log-normal size distribution parameters increases as the aerosol load decreases. Similarly, the reduction in the spectral range diminishes the stability of the retrieved parameters. In addition to these numerical studies, we used optical depth observations at eight AERONET locations to validate our results with the standard AERONET inversion products. We found that bimodal log-normal size distributions serve as useful input assumptions, especially when the measurements have inadequate spectral coverage and/or limited accuracy, such as moon photometry. Comparisons of the mode median radii between GRASP-AOD and AERONET indicate average differences of 0.013 µm for the fine mode and typical values of 0.2–0.3 µm for the coarse mode. The dominant mode (i.e. fine or coarse) indicates a 10 % difference in mode radii between the GRASP-AOD and AERONET inversions, and the average of the difference in volume concentration is around 17 % for both modes. The retrieved values of the fine-mode τa(500) using GRASP-AOD are generally between those values obtained by the standard AERONET inversion and the values obtained by the AERONET spectral deconvolution algorithm (SDA), with differences typically lower than 0.02 between GRASP-AOD and both algorithms. Finally, we present some examples of application of GRASP-AOD inversion using moon photometry and the airborne PLASMA sun photometer during the ChArMEx summer 2013 campaign in the western Mediterranean.

scholarly journals Advanced characterization of aerosol properties from measurements of spectral optical depth using the GRASP algorithm

2016 ◽  
Author(s):  
Benjamin Torres ◽  
Oleg Dubovik ◽  
David Fuertes ◽  
Gregory Schuster ◽  
Victoria Eugenia Cachorro ◽  
...  
Keyword(s):  
Optical Depth ◽  
Atmospheric Aerosols ◽  
A Priori ◽  
Advanced Characterization ◽  
Western Mediterranean ◽  
Coarse Mode ◽  
Fine Mode ◽  
Priori Information ◽  
Log Normal ◽  
Mode Volume

Abstract. This study evaluates the potential of using aerosol optical depth (τa) measurements to characterize the microphysical and optical properties of atmospheric aerosols. With this aim, we used the recently developed GRASP (Generalized Retrieval of Aerosol and Surface Properties) code for numerical testing of six different aerosol models with three different aerosol loads. We found that bimodal log-normal size distributions serve as useful input assumptions, especially when the measurements have inadequate spectral coverage and/or limited accuracy, such as lunar photometry. The direct numerical simulations indicate that the GRASP-AOD retrieval provides modal aerosol optical depths (fine and coarse) to within 0.01 of the input values. The retrieval of the fine mode radius, width, and volume concentration is stable and precise if the real part of the refractive index is known. The coarse mode properties are less accurate, but they are significantly improved when additional a priori information is available. In addition to these numerical studies, we used optical depth observations at six AERONET locations to validate our results with the standard AERONET inversion products. Differences in the fine mode volume median radii for the GRASP-AOD and AERONET inversions are less than 0.02 μm at sites dominated by the fine mode for all cases, although they are typically less than 0.01 μm when τa(440) > 0.3. The comparison of the coarse mode volume median radii shows larger differences than the fine mode at the same sites, with values typically between 0.2–0.3 μm. The comparison of coarse mode volume median radii between GRASP-AOD and AERONET improves for sites dominated by desert dust aerosol, with differences of less than 0.2 μm in most cases. The retrieved values of the fine-mode τa(500) using GRASP-AOD are generally between those values obtained by the standard AERONET inversion and the values obtained by the advance AERONET Spectral Deconvolution Algorithm (SDA), with differences typically lower than 0.02 between GRASP-AOD and both algorithms. Finally, we present some examples of application of GRASP-AOD inversion using moon-photometry and the airborne PLASMA sun-photometer during ChArMEx summer 2013 campaign in the western Mediterranean.

scholarly journals Observation of atmospheric aerosols at Mt. Hua and Mt. Tai in central and east China during spring 2009 – Part 1: EC, OC and inorganic ions

2011 ◽  
Vol 11 (9) ◽  
pp. 4221-4235 ◽  
Author(s):  
G. Wang ◽  
J. Li ◽  
C. Cheng ◽  
S. Hu ◽  
M. Xie ◽  
...  
Keyword(s):  
Atmospheric Aerosols ◽  
Dust Storm ◽  
Fine Particles ◽  
Ph Value ◽  
Inorganic Ions ◽  
East China ◽  
Storm Event ◽  
Ph Values ◽  
Coarse Mode ◽  
Dust Storm Event

Abstract. PM10 and size-segregated samples were simultaneously collected at Mt. Hua (2060 m a.s.l.) and Mt. Tai (1545 m a.s.l.) in central and east coastal China during spring, 2009 including an intensive dust storm event occurring on 24 April, and determined for EC, OC and inorganic ions. During the non-dust storm period particles, EC, OC and ions except for SO42− were 2–10 times more abundant at Mt. Tai than at Mt. Hua. SO42− (13 ± 7.1 μg m−3) at Mt. Hua was the dominant ion, followed by NO3− (5.0 ± 3.9 μg m−3), NH4+ (2.5 ± 1.3 μg m−3) and Ca2+ (1.6 ± 0.8 μg m−3). In contrast, at Mt. Tai NO3− was most abundant (20 ± 14 μg m−3), followed by SO42− (16 ± 13 μg m−3), NH4+ (12 ± 8.9 μg m−3) and Ca2+ (3.9 ± 2.1 μg m−3). The fact of NO3− exceeding over SO42− at Mt. Tai may suggest the changes in chemical composition of the atmosphere over east China due to sharply increasing vehicle emission. pH values of the water-extracts of PM10 samples indicate that at the two mountain sites aerosols transported from the south regions are more acidic than those from the north and more acidic at Mt. Tai than at Mt. Hua during the non-dust storm period. During the dust storm event particle mass, OC, Na+, K+, Mg2+ and Ca2+ at both sites increased by a factor of 1–9, while EC, NO3− and NH4+ decreased by 20–80 %. However, SO42− concentrations (13 ± 7.7 μg m−3 at Mt. Hua and 15 ± 5.6 μg m−3 at Mt. Tai, respectively) at the two sites during the episode were comparable and did not change significantly compared to those in the non-dust storm period, probably due to a similar level of free tropospheric SO2 in central and east China. Compared with those at Mt. Hua the coarse modes (>2.1 μm) of K+ and SO42− at Mt. Tai during the non-event period were more abundant and the coarse mode of NO3− was less abundant. When the dust storm was present all ions significantly moved toward coarse particles, except for NH4+, with a disappeared peak in fine mode (<2.1 μm) for NO3−. Linear regression for ion equivalents in fine particles indicates that ammonium exists in the forms of NH4NO3 and NH4HSO4 at Mt. Hua and NH4NO3 and (NH4)2SO4 at Mt. Tai during both the nonevent and the event periods. While the regression for coarse mode of Ca2+ suggests a close coupling of dust with nitrate during the nonevent time and with sulfate during the dust-storm period. pH values of the size-resolved samples further suggest that during the nonevent period most acidic particles at Mt. Hua are in the range of 0.7–1.1 μm, while those at Mt. Tai are in the range of 1.1–2.1 μm. Aerosols at both sites became alkaline during the event, but the Mt. Tai particles still showed a lower pH value.

scholarly journals Sources of anions in aerosols in northeast Greenland during late winter

2012 ◽  
Vol 12 (6) ◽  
pp. 14813-14836 ◽  
Author(s):  
M. Fenger ◽  
L. L. Sørensen ◽  
K. Kristensen ◽  
B. Jensen ◽  
Q. T. Nquyen ◽  
...  
Keyword(s):  
Sea Ice ◽  
Long Range ◽  
Atmospheric Aerosols ◽  
Fine Particles ◽  
Chemical Properties ◽  
High Arctic ◽  
Early Spring ◽  
Water Soluble ◽  
The Arctic ◽  
Late Winter

Abstract. The knowledge of climate effects of atmospheric aerosols is associated with large uncertainty, and a better understanding of their physical and chemical properties is needed, especially in the Arctic environment. The objective of the present study is to improve our understanding of the processes affecting the composition of the aerosols in the high Arctic. Therefore size-segregated aerosols were sampled at a high Arctic site, Station Nord (Northeast Greenland), in March 2009 using a Micro Orifice Uniform Deposit Impactor. The aerosol samples were extracted in order to analyze the three water-soluble anions: chloride, nitrate and sulphate. The results are discussed based on possible chemical and physical transformations as well as transport patterns. The total concentrations of the ions at Station Nord were 53–507 ng m−3, 2–298 ng m−3 and 535–1087 ng m−3 for chloride (Cl−), nitrate (NO3-) and sulphate (SO42−), respectively. The aerosols in late winter/early spring, after polar sunrise, are found to be a mixture of long-range transported and regional to local originating aerosols. Fine particles, smaller than 1 μm, containing SO42−, Cl− and NO3−, are hypothesized to originate from long-range transport, where SO42− is by far the dominating anion accounting for 50–85% of the analyzed mass. The analysis suggests that Cl− and NO3− in coarser particles (>1.5 μm) originate from local/regional sources. Under conditions where the air mass is transported over sea-ice at high wind speeds, very coarse particles (>18 μm) are observed and it is hypothesized that frost flowers on the sea ice is a source of very coarse chloride particles in the Arctic.

scholarly journals Fossil and Non-Fossil Sources of Different Carbonaceous Fractions in Fine and Coarse Particles by Radiocarbon Measurement

Radiocarbon ◽  
2013 ◽  
Vol 55 (3) ◽  
pp. 1510-1520 ◽  
Author(s):  
Y L Zhang ◽  
P Zotter ◽  
N Perron ◽  
A S H Prévôt ◽  
L Wacker ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Fine Particles ◽  
Water Soluble ◽  
Coarse Particles ◽  
Carbonaceous Particles ◽  
Fossil Carbon ◽  
Coarse Mode ◽  
Wood Burning ◽  
Inorganic Substances ◽  
Secondary Formation

Radiocarbon offers a unique possibility for unambiguous source apportionment of carbonaceous particles due to a direct distinction of non-fossil and fossil carbon. In this work, particulate matter of different size fractions was collected at 4 sites in Switzerland to examine whether fine and coarse carbonaceous particles exhibit different fossil and contemporary sources. Elemental carbon (EC) and organic carbon (OC) as well as water-soluble OC (WSOC) and water-insoluble OC (WINSOC) were separated and determined for subsequent 14C measurement. In general, both fossil and non-fossil fractions in OC and EC were found more abundant in the fine than in the coarse mode. However, a substantial fraction (∼20 ± 5%) of fossil EC was found in coarse particles, which could be attributed to traffic-induced non-exhaust emissions. The contribution of biomass burning to coarse-mode EC in winter was relatively high, which is likely associated to the coating of EC with organic and/or inorganic substances emitted from intensive wood burning. Further, fossil OC (i.e. from vehicle emissions) was found to be smaller than non-fossil OC due to the presence of primary biogenic OC and/or growing in size of wood-burning OC particles during aging processes. 14C content in WSOC indicated that the second organic carbon rather stems from non-fossil precursors for all samples. Interestingly, both fossil and non-fossil WINSOC concentrations were found to be higher in fine particles than in coarse particles in winter, which is likely due to primary wood burning emissions and/or secondary formation of WINSOC.

scholarly journals Sources of anions in aerosols in northeast Greenland during late winter

2013 ◽  
Vol 13 (3) ◽  
pp. 1569-1578 ◽  
Author(s):  
M. Fenger ◽  
L. L. Sørensen ◽  
K. Kristensen ◽  
B. Jensen ◽  
Q. T. Nguyen ◽  
...  
Keyword(s):  
Sea Ice ◽  
Long Range ◽  
Atmospheric Aerosols ◽  
Fine Particles ◽  
Chemical Properties ◽  
High Arctic ◽  
Early Spring ◽  
Water Soluble ◽  
The Arctic ◽  
Late Winter

Abstract. The knowledge of climate effects of atmospheric aerosols is associated with large uncertainty, and a better understanding of their physical and chemical properties is needed, especially in the Arctic environment. The objective of the present study is to improve our understanding of the processes affecting the composition of aerosols in the high Arctic. Therefore size-segregated aerosols were sampled at a high Arctic site, Station Nord (Northeast Greenland), in March 2009 using a Micro Orifice Uniform Deposit Impactor. The aerosol samples were extracted in order to analyse three water-soluble anions: chloride, nitrate and sulphate. The results are discussed based on possible chemical and physical transformations as well as transport patterns. The total concentrations of the ions at Station Nord were 53–507 ng m−3, 2–298 ng m−3 and 535–1087 ng m−3 for chloride (Cl−), nitrate (NO3−) and sulphate (SO42−), respectively. The aerosols in late winter/early spring, after polar sunrise, are found to be a mixture of long-range transported and regional to local originating aerosols. Fine particles, smaller than 1 μm, containing SO42−, Cl− and NO3−, are hypothesized to originate from long-range transport, where SO42− is by far the dominating anion accounting for 50–85% of the analyzed mass. The analysis suggests that Cl− and NO3− in coarser particles (> 1.5 μm) originate from local/regional sources. Under conditions where the air mass is transported over sea ice at high wind speeds, very coarse particles (> 18 μm) are observed, and it is hypothesized that frost flowers on the sea ice are a source of the very coarse nitrate particles.

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