scholarly journals Effects of black carbon morphology on the brown carbon absorption estimation: from numerical aspects

2020 ◽  
Author(s):  
Jie Luo ◽  
Yongming Zhang ◽  
Qixing Zhang
Keyword(s):  
Fractal Dimension ◽  
Numerical Method ◽  
Black Carbon ◽  
Cross Section ◽  
Absorption Cross Section ◽  
Accurate Estimation ◽  
Total Absorption ◽  
Absorption Cross ◽  
Brown Carbon ◽  
Carbon Absorption

Abstract. In this work, we developed a numerical method to investigate the effects of black carbon morphology on the estimation of brown carbon (BrC) absorption using the Absorption Ångström exponent (AAE) method. Pseudo measurements of the total absorption were generated based on several morphologically mixed black carbon (BC) models, then the BrC absorption was inferred based on different AAE methods. By comparing the estimated BrC absorption with True BrC absorption, we found that both AAE = 1 and Mie AAE methods do not provide accurate estimation for the BrC absorption, and the estimated BrC absorption can deviate several times from True BrC absorption. The newly proposed Wavelength Dependent AAE (WDA) method does not necessarily improve the estimations, sometimes it may even provide worse estimations than the AAE = 1 and Mie AAE methods. Fixing the fractal dimension to be 1.8, the deviation between the estimated BrC mass absorption cross-section (MAC) and True BrC MAC can reach approximately 9 m2/g, which is far more than brown carbon MAC itself. Therefore, the estimation of BrC absorption based on the AAE method should carefully consider the morphological effects of BC. Our findings highlight the BC morphological effects on the BrC absorption estimation.

scholarly journals Black carbon over Mexico: the effect of atmospheric transport on mixing state, mass absorption cross-section, and BC/CO ratios

2010 ◽  
Vol 10 (1) ◽  
pp. 219-237 ◽  
Author(s):  
R. Subramanian ◽  
G. L. Kok ◽  
D. Baumgardner ◽  
A. Clarke ◽  
Y. Shinozuka ◽  
...  
Keyword(s):  
Black Carbon ◽  
Mexico City ◽  
Cross Section ◽  
Absorption Cross Section ◽  
Atmospheric Transport ◽  
Absorption Cross ◽  
Air Masses ◽  
Wet Scavenging ◽  
The City ◽  
Absorption Photometer

Abstract. A single particle soot photometer (SP2) was operated on the NCAR C-130 during the MIRAGE campaign (part of MILAGRO), sampling black carbon (BC) over Mexico. The highest BC concentrations were measured over Mexico City (sometimes as much as 2 μg/m3) and over hill-fires to the south of the city. The age of plumes outside of Mexico City was determined using a combination of HYSPLIT trajectories, WRF-FLEXPART modeling and CMET balloon tracks. As expected, older, diluted air masses had lower BC concentrations. A comparison of carbon monoxide (CO) and BC suggests a CO background of around 65 ppbv, and a background-corrected BC/COnet ratio of 2.89±0.89 (ng/m3-STP)/ppbv (average ± standard deviation). This ratio is similar for fresh emissions over Mexico City, as well as for aged airmasses. Comparison of light absorption measured with a particle soot absorption photometer (PSAP) and the SP2 BC suggests a BC mass-normalized absorption cross-section (MAC) of 10.9±2.1 m2/g at 660 nm (or 13.1 m2/g @ 550 nm, assuming MAC is inversely dependent on wavelength). This appears independent of aging and similar to the expected absorption cross-section for aged BC, but values, particularly in fresh emissions, could be biased high due to instrument artifacts. SP2-derived BC coating indicators show a prominent thinly-coated BC mode over the Mexico City Metropolitan Area (MCMA), while older air masses show both thinly-coated and thickly-coated BC. Some 2-day-old plumes do not show a prominent thickly-coated BC mode, possibly due to preferential wet scavenging of the likely-hydrophilic thickly-coated BC.

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.

Sign in / Sign up

Export Citation Format

Share Document