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 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 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.

Sign in / Sign up

Export Citation Format

Share Document