scholarly journals Modification in light absorption cross section of laboratory-generated black carbon-brown carbon particles upon surface reaction and hydration

2015 ◽  
Vol 116 ◽  
pp. 253-261 ◽  
Author(s):  
Hui Chen ◽  
Dawei Hu ◽  
Lin Wang ◽  
Abdelwahid Mellouki ◽  
Jianmin Chen
Keyword(s):  
Black Carbon ◽  
Cross Section ◽  
Light Absorption ◽  
Absorption Cross Section ◽  
Surface Reaction ◽  
Absorption Cross ◽  
Brown Carbon ◽  
Carbon Particles

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 Estimation of the mass absorption cross section of the organic carbon component of aerosols in the Mexico City Metropolitan Area (MCMA)

2008 ◽  
Vol 8 (3) ◽  
pp. 10189-10225 ◽  
Author(s):  
J. C. Barnard ◽  
R. Volkamer ◽  
E. I. Kassianov
Keyword(s):  
Organic Carbon ◽  
Black Carbon ◽  
Mexico City ◽  
Cross Section ◽  
Light Absorption ◽  
Absorption Cross Section ◽  
Trace Gases ◽  
Absorption Cross ◽  
Enhanced Absorption ◽  
Mass Absorption

Abstract. Data taken from the MCMA-2003 and the 2006 MILAGRO field campaigns are used to examine the absorption of solar radiation by the organic component of aerosols. Using irradiance data from a Multi-Filter Rotating Shadowband Radiometer (MFRSR) and an actinic flux spectroradiometer (SR), we derive aerosol single scattering albedo, π0,λ, as a function of wavelength, λ. We find that in the near-UV spectral range (250 to 400 nm) π0,λ is much lower compared to π0,λ at 500 nm indicating enhanced absorption in the near-UV range. Absorption by elemental carbon, dust, or gas cannot account for this enhanced absorption leaving the organic part of the aerosol as the only possible absorber. We use data from a surface deployed Aerodyne Aerosol Mass Spectrometer (AMS) along with the inferred π0,λ to estimate the Mass Absorption Cross section (MAC) for the organic carbon. We find that the MAC is about 10.5 m2/g at 300 nm and falls close to zero at about 500 nm; values that are roughly consistent with other estimates of organic carbon MAC. These MAC values can be considered as "radiatively correct" because when used in radiative transfer calculations the calculated irradiances/actinic fluxes match those measured at the wavelengths considered here. For an illustrative case study described here, we estimate that the light absorption by the "brown" (organic) carbonaceous aerosol can add about 40% to the light absorption of black carbon in Mexico City. This contribution will vary depending on the relative abundance of organic carbon relative to black carbon. Furthermore, our analysis indicates that organic aerosol would slow down photochemistry by selectively scavenging the light reaching the ground at those wavelengths that drive photochemical reactions. Finally, satellite retrievals of trace gases that are used to infer emissions currently assume that the MAC of organic carbon is zero. For trace gases that are retrieved using wavelengths shorter then 420 nm (i.e. SO2, HCHO, halogenoxides, NO2), the assumption of non-zero MAC values will induce an upward correction to the inferred emissions. This will be particularly relevant in polluted urban atmospheres and areas of biomass burning where organic aerosols are particularly abundant.

scholarly journals Determination of black carbon mass concentration from aerosol light absorption using variable mass absorption cross-section

2020 ◽  
Author(s):  
Weilun Zhao ◽  
Wangshu Tan ◽  
Gang Zhao ◽  
Chuanyang Shen ◽  
Yingli Yu ◽  
...  
Keyword(s):  
Absorption Coefficient ◽  
Black Carbon ◽  
Cross Section ◽  
Light Absorption ◽  
Absorption Cross Section ◽  
Traditional Method ◽  
Mass Concentration ◽  
New Method ◽  
Absorption Cross ◽  
Light Absorption Coefficient

Abstract. Atmospheric black carbon (BC) is the strongest visible solar radiative absorber in the atmosphere, exerting significant influences on the earth’s radiation budget. The mass absorption cross-section (MAC) is a crucial parameter for converting light absorption coefficient (bab) to mass equivalent BC concentration (mBC). Traditional filter-based instrument, such as AE33, uses a constant MAC of 7.77 m2/g to derive mBC, which may lead to uncertainty in mBC. In this paper, a new method of converting light absorption coefficient to BC mass concentration is proposed by incorporating the variations of MAC attributed to the influences of aerosol coating state. Mie simulation showed that MAC varied dramatically with different core-shell structures. We compared our new method with traditional method during a field measurement at a site of North China Plain. The results showed that the MAC was smaller (larger) than 7.77 m2/g for particle smaller (larger) than 280 nm, resulting in BC mass size distribution derived from new method was higher (lower) than traditional method for particle smaller (larger) than 280 nm. Size-integrated BC mass concentration derived from new method was 16 % higher than traditional method. Sensitivity analysis indicated that the uncertainty in mBC caused by refractive index (RI) was with in 35 % and the imaginary part of RI had dominant influence on the derived mBC. This study emphasizes the necessity to take variations of MAC into account when deriving mBC from bab and can help constrain the uncertainty in mBC measurements.

scholarly journals Determination of equivalent black carbon mass concentration from aerosol light absorption using variable mass absorption cross section

2021 ◽  
Vol 14 (2) ◽  
pp. 1319-1331
Author(s):  
Weilun Zhao ◽  
Wangshu Tan ◽  
Gang Zhao ◽  
Chuanyang Shen ◽  
Yingli Yu ◽  
...  
Keyword(s):  
Black Carbon ◽  
Cross Section ◽  
Light Absorption ◽  
Absorption Cross Section ◽  
Traditional Method ◽  
Mass Concentration ◽  
New Method ◽  
Radiation Budget ◽  
Absorption Cross ◽  
Mass Absorption

Abstract. Atmospheric black carbon (BC) is the strongest solar radiative absorber in the atmosphere, exerting significant influences on the earth's radiation budget. The mass absorption cross section (MAC) is a crucial parameter for converting the light absorption coefficient (σab) to the equivalent BC mass concentration (EBC). Traditional filter-based instruments, such as the AE33, use a constant MAC of 7.77 m2/g at 880 nm to derive the EBC, which may lead to uncertainty in the EBC. In this paper, a new method of converting σab to the EBC is proposed by incorporating the variations of the MAC attributed to the influences of the aerosol coating state. A Mie simulation showed that the MAC varied dramatically with different core sizes and shell thicknesses. We compared our new method with the traditional method during a field measurement at a site on the North China Plain. The results showed that the MAC at 880 nm was smaller (larger) than 7.77 m2/g for particles smaller (larger) than 280 nm, resulting in an EBC mass size distribution derived from the new method that was higher (lower) than the traditional method for particles smaller (larger) than 280 nm. The size-integrated EBC derived from the new method was 16 % higher than that derived from the traditional method. Sensitivity analysis indicated that the uncertainty in the EBC caused by the refractive index (RI) was within 35 %, and the imaginary part of the RI had dominant influence on the derived EBC. This study emphasizes the necessity to take variations of the MAC into account when deriving the EBC from σab and can help constrain the uncertainty in EBC measurements.

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.

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