scholarly journals Climatology of aerosol optical properties and black carbon mass absorption cross section at a remote high altitude site in the Western Mediterranean Basin

2014 ◽  
Vol 14 (3) ◽  
pp. 3777-3814 ◽  
Author(s):  
M. Pandolfi ◽  
A. Ripoll ◽  
X. Querol ◽  
A. Alastuey
Keyword(s):  
Black Carbon ◽  
Cross Section ◽  
Absorption Cross Section ◽  
Mediterranean Basin ◽  
Western Mediterranean ◽  
Absorption Cross ◽  
African Dust ◽  
Mass Absorption ◽  
Western Mediterranean Basin ◽  
Carbon Mass

Abstract. Aerosol light scattering, backscattering and absorption were measured at Montsec (MSC; 42°3' N, 0°44' E, 1570 m a.s.l.), a remote high-altitude site in the Western Mediterranean Basin. Mean (± sd) scattering, hemispheric backscattering and absorption were 18.9 ± 20.8 Mm−1, 2.6 ± 2.8 Mm−1 and 1.5 ± 1.4 Mm−1, respectively at 635 nm during the period under study (June 2011–June 2013). Mean values of single scattering albedo (635 nm), scattering Ångström exponent (450–635 nm), backscatter-to-scatter ratio (635 nm), asymmetry parameter (635 nm) and black carbon mass absorption cross section (637 nm) were 0.92 ± 0.03, 1.56 ± 0.88, 0.16 ± 0.09, 0.53 ± 0.16 and 10.9 ± 3.5 m2 g−1 respectively. The scattering measurements performed at MSC locate this site in the medium/upper range of values reported for other mountaintop sites in Europe mainly due to the frequent African dust episodes and regional recirculation scenarios occurring mostly in spring/summer and causing the presence of polluted layers at the MSC altitude. Under these conditions no clear diurnal cycles were observed for the measured extensive aerosol optical properties (scattering, absorption and extinction). Conversely, the mean particle absorption at MSC was relatively lower compared with other EU remote stations thus leading to relatively higher single scattering albedo compared with most European data. A season-dependent decrease in the magnitude of aerosol extensive properties was observed when MSC was in the free troposphere with the highest free-troposphere vs. all-data difference observed in winter and the lowest in spring/summer. The slope of the scattering vs. absorption relationship (among the lowest reported for other mountain top sites worldwide) indicates that the MSC site is dominated by dust aerosols at high aerosol loading. Correspondingly, scattering Ångström exponent and asymmetry parameter respectively decreased and increased indicating the shift toward larger particles associated with African dust episodes. The black carbon mass absorption cross section showed a clear annual cycle with higher values in summer when the occurrence of African dust outbreaks and regional recirculation scenarios favour the presence of aged black carbon particles in polluted layers at the MSC altitudes. The optical measurements performed at the MSC remote site were compared with those simultaneously performed at a regional background station in the Western Mediterranean Basin.

scholarly journals Climatology of aerosol optical properties and black carbon mass absorption cross section at a remote high-altitude site in the western Mediterranean Basin

2014 ◽  
Vol 14 (12) ◽  
pp. 6443-6460 ◽  
Author(s):  
M. Pandolfi ◽  
A. Ripoll ◽  
X. Querol ◽  
A. Alastuey
Keyword(s):  
Optical Properties ◽  
Cross Section ◽  
Asymmetry Parameter ◽  
Mediterranean Basin ◽  
Western Mediterranean ◽  
Free Troposphere ◽  
Absorption Cross ◽  
Aerosol Optical Properties ◽  
Western Mediterranean Basin ◽  
Carbon Mass

Abstract. Aerosol light scattering (σsp), backscattering (σbsp) and absorption (σap) were measured at Montsec (MSC; 42°3' N, 0°44' E, 1570 m a.s.l.), a remote high-altitude site in the western Mediterranean Basin. Mean (±SD) σsp, σbsp and σap were 18.9 ± 20.8, 2.6 ± 2.8 and 1.5 ± 1.4 Mm−1, respectively at 635 nm during the period under study (June 2011–June 2013). Mean values of single-scattering albedo (SSA, 635 nm), the scattering Ångström exponent (SAE, 450–635 nm), backscatter-to-scatter ratio (B / S, 635 nm), asymmetry parameter (g, 635 nm), black carbon mass absorption cross section (MAC, 637 nm) and PM2.5 mass scattering cross section (MSCS, 635 nm) were 0.92 ± 0.03, 1.56 ± 0.88, 0.16 ± 0.09, 0.53 ± 0.16, 10.9 ± 3.5 m2 g−1 and 2.5 ± 1.3 m2 g−1, respectively. The scattering measurements performed at MSC were in the medium/upper range of values reported by Andrews et al. (2011) for other mountaintop sites in Europe due to the frequent regional recirculation scenarios (SREG) and Saharan dust episodes (NAF) occurring mostly in spring/summer and causing the presence of polluted layers at the MSC altitude. However, the development of upslope winds and the possible presence of planetary boundary layer air at MSC altitude in summer may also have contributed to the high scattering observed. Under these summer conditions no clear diurnal cycles were observed for the measured extensive aerosol optical properties (σsp, σbsp and σap). Conversely, low σsp and σap at MSC were measured during Atlantic advections (AA) and winter regional anticyclonic episodes (WREG) typically observed during the cold season in the western Mediterranean. Therefore, a season-dependent decrease in the magnitude of aerosol extensive properties was observed when MSC was in the free troposphere, with the highest free-troposphere vs. all-data difference observed in winter and the lowest in spring/summer. The location of MSC station allowed for a reliable characterization of aerosols as a function of the main synoptic meteorological patterns. The SAE was the lowest during NAF and showed an inverse correlation with the outbreak intensity, indicating a progressive shift toward larger particles. Moreover, the strength of NAF episodes in the region led to a slope of the scattering vs. absorption relationship among the lowest reported for other mountaintop sites worldwide, indicating that MSC was dominated by dust aerosols at high aerosol loading. As a consequence, SSA showed a nearly monotonic increase with increasing particle concentration and scattering. The SAE was the highest during SREG, indicating the presence of polluted layers dominated by smaller particles. Correspondingly, the asymmetry parameter was lower under SREG compared with NAF. The MAC and MSCS were significantly higher during NAF and SREG compared to AA and WREG, indicating an increase of absorption and scattering efficiencies associated with the summer polluted scenarios. The optical measurements performed at the MSC remote site were compared with those simultaneously performed at a regional background station in the western Mediterranean Basin located at around 700 m a.s.l. upstream of the MSC station.

scholarly journals Variability in the mass absorption cross-section of black carbon (BC) aerosols is driven by BC internal mixing state at a central European background site (Melpitz, Germany) in winter

2020 ◽  
Author(s):  
Jinfeng Yuan ◽  
Robin Lewis Modini ◽  
Marco Zanatta ◽  
Andreas B. Herber ◽  
Thomas Müller ◽  
...  
Keyword(s):  
Size Distribution ◽  
Black Carbon ◽  
Cross Section ◽  
Coating Thickness ◽  
Absorption Cross Section ◽  
Correlation Method ◽  
Absorption Cross ◽  
Core Size ◽  
Background Site ◽  
Mass Absorption

Abstract. Properties of atmospheric black carbon (BC) particles were characterized during a field experiment at a rural background site (Melpitz, Germany) in February 2017. BC absorption at a wavelength of 870 nm was measured by a photoacoustic extinctiometer and BC physical properties (BC mass concentration, core size distribution and coating thickness) were measured by a single-particle soot photometer (SP2). Additionally, a catalytic stripper was used to intermittently remove BC coatings by alternating between ambient and thermo-denuded conditions. From these data the mass absorption cross section of BC (MACBC) and its enhancement factor (EMAC) were inferred. Two methods were applied independently to investigate the coating effect on EMAC: a correlation method (ambient MACBC vs. BC coating thickness) and a denuding method (MACBC,amb vs. MACBC,denuded). Observed EMAC values varied from 1.0 to 1.6 (lower limit from denuding method) or ~ 1.2 to 1.9 (higher limit from correlation method) with the mean coating volume fraction ranging from 54 to 78 % in the dominating mass equivalent BC core diameter range of 200–220 nm. MACBC and EMAC were strongly correlated with coating thickness of BC, while other factors were found to have a potential minor influence as well, including air mass origins (different BC sources), mixing morphology (ratio of inorganics to organics), BC core size distribution and absorption Ångström exponent (AAE). These results for ambient BC measured at Melpitz during winter show that the lensing effect caused by coatings on BC is the main driver of the variations in MACBC and EMAC, while changes in other BC particle properties such as source, BC core size or coating composition play only minor roles.

Mass Absorption Cross-Section of Ambient Black Carbon Aerosol in Relation to Chemical Age

2009 ◽  
Vol 43 (6) ◽  
pp. 522-532 ◽  
Author(s):  
A. Knox ◽  
G. J. Evans ◽  
J. R. Brook ◽  
X. Yao ◽  
C.-H. Jeong ◽  
...  
Keyword(s):  
Black Carbon ◽  
Cross Section ◽  
Absorption Cross Section ◽  
Absorption Cross ◽  
Mass Absorption ◽  
Black Carbon Aerosol

scholarly journals Black carbon physical and optical properties across northern India during pre-monsoon and monsoon seasons

2019 ◽  
Vol 19 (20) ◽  
pp. 13079-13096 ◽  
Author(s):  
James Brooks ◽  
Dantong Liu ◽  
James D. Allan ◽  
Paul I. Williams ◽  
Jim Haywood ◽  
...  
Keyword(s):  
Black Carbon ◽  
Cross Section ◽  
Coating Thickness ◽  
Absorption Cross Section ◽  
Absorption Cross ◽  
North West ◽  
North East India ◽  
Mass Absorption ◽  
North East ◽  
The North

Abstract. Black carbon (BC) is known to have major impacts on both climate and human health and is therefore of global importance, particularly in regions close to large populations that have strong sources. The size-resolved mixing state of BC-containing particles was characterised using a single-particle soot photometer (SP2). The study focusses on the Indo-Gangetic Plain (IGP) during the pre-monsoon and monsoon seasons. Data presented are from the UK Facility for Airborne Atmospheric Measurements BAe-146 research aircraft that performed flights during the pre-monsoon (11 and 12 June) and monsoon (30 June to 11 July) seasons of 2016. Over the IGP, BC mass concentrations were greater (1.95 µg m−3) compared to north-west India (1.50 µg m−3) and north-east India (0.70 µg m−3) during the pre-monsoon season. Across northern India, two distinct BC modes were recorded; a mode of small BC particles (core diameter <0.16 µm and coating thickness <50 nm) and a mode of moderately coated BC (core diameter <0.22 µm and coating thickness of 50–200 nm). The IGP and north-east India locations exhibited moderately coated black carbon particles with enhanced coating thicknesses, core sizes, mass absorption cross sections, and scattering enhancement values compared to much lower values present in the north-west. The coating thickness and mass absorption cross section increased with altitude (13 %) compared to those in the boundary layer. As the monsoon arrived across the region, mass concentration of BC decreased over the central IGP and north-east locations (38 % and 28 % respectively), whereas for the north-west location BC properties remained relatively consistent. Post-monsoon onset, the coating thickness, core size, mass absorption cross section, and scattering enhancement values were all greatest over the central IGP much like the pre-monsoon season but were considerably reduced over both north-east and north-west India. Increases in mass absorption cross section through the atmospheric column were still present during the monsoon for the north-west and central IGP locations, but less so over the north-east due to lack of long-range transport aerosol aloft. Across the Indo-Gangetic Plain and north-east India during the pre-monsoon and monsoon seasons, solid-fuel (wood burning) emissions form the greatest proportion of BC with moderately coated particles. However, as the monsoon develops in the north-east there was a switch to small uncoated BC particles indicative of traffic emissions, but the solid-fuel emissions remained in the IGP into the monsoon. For both seasons in the north-west, traffic emissions form the greatest proportion of BC particles. Our findings will prove important for greater understanding of the BC physical and optical properties, with important consequences for the atmospheric radiative forcing of BC-containing particles. The findings will also help constrain the regional aerosol models for a variety of applications such as space-based remote sensing, chemistry transport modelling, air quality, and BC source and emission inventories.

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