A physically‐based treatment of elemental carbon optics: Implications for global direct forcing of aerosols

Jacobson, Mark Z.

doi:10.1029/1999gl010968

Cited by 498 publications

(412 citation statements)

References 39 publications

Supporting

Mentioning

389

Contrasting

Unclassified

Order By: Relevance

“…Second, hygroscopic growth factors are smaller for SDE particles than for the common JFJ aerosol (Weingartner et al, 2001). Third, it has been shown that the wavelength dependence of the absorption coefficient is very similar in the 0.45-1.0 µm region for externally mixed, internally mixed and shell-core configurations of black carbon (Jacobson, 2000). Since the aerosol reaching the JFJ is aged and therefore internally mixed, α ap will probably exhibit only a slight variation with humidity.…”

Section: Resultsmentioning

confidence: 99%

Saharan dust events at the Jungfraujoch: detection by wavelength dependence of the single scattering albedo and first climatology analysis

et al. 2004

View full text Add to dashboard Cite

Abstract. Scattering and absorption coefficients have been measured continuously at several wavelengths since March 2001 at the high altitude site Jungfraujoch (3580 m a.s.l.). From these data, the wavelength dependences of the Angström exponent and particularly of the single scattering albedo are determined. While the exponent of the single scattering albedo usually increases with wavelength, it decreases with wavelength during Saharan dust events (SDE) due to the greater size of the mineral aerosol particles and their different chemical composition. This change in the sign of the single scattering exponent turns out to be a sensitive means for detecting Saharan dust events. The occurrence of SDE detected by this new method was confirmed by visual inspection of filter colors and by studying long-range backtrajectories. An examination of SDE over a 22-month period shows that SDE are more frequent during the March-June period as well as during October and November. The trajectory analysis indicated a mean traveling time of 96.5 h, with the most important source countries situated in the northern and north-western part of the Saharan desert. Most of the SDE do not lead to a detectable increase of the 48-h total suspended particulate matter (TSP) concentration at the Jungfraujoch. During Saharan dust events, the average contribution of this dust to hourly TSP at the Jungfraujoch is 16 µg/m 3 , which corresponds to an annual mean of 0.8 µg/m 3 or 24% of TSP.

show abstract

Section: Resultsmentioning

confidence: 99%

Saharan dust events at the Jungfraujoch: detection by wavelength dependence of the single scattering albedo and first climatology analysis

et al. 2004

View full text Add to dashboard Cite

show abstract

“…It is now well established that neglecting morphological properties by employing over-simplified shape models, such as the homogeneous sphere approximation, can significantly impair estimates of the direct climate, forcing impact of aerosols (Jacobson 2000;Kahnert et al 2007). However, increasing the complexity of model particles is no guarantee for yielding better estimates of the optical properties (Veihelmann et al 2006).…”

Section: Properties Of Externally Mixed Lacmentioning

confidence: 99%

On the Discrepancy between Modeled and Measured Mass Absorption Cross Sections of Light Absorbing Carbon Aerosols

Kahnert

2010

Aerosol Science and Technology

View full text Add to dashboard Cite

Recent modeling studies based on the Rayleigh-Debye-Gans (RDG) approximation have revealed a discrepancy between modeled and measured mass absorption cross sections (MAC) for atmospheric light absorbing carbon (LAC) aerosols. One plausible explanation is that this discrepancy is due to errors introduced by neglecting electromagnetic interactions among monomers in LAC aggregates within the RDG approximation. Here we compute MAC by use of numerically exact solutions to Maxwell's equations and investigate the sensitivity of the results to a variation in the aggregates' physical properties and refractive index. The results do confirm that approximate methods can introduce large errors in the results for the optical properties. However, these errors alone cannot explain the discrepancy between measured and modeled values of MAC. An agreement between observations and theoretical results can only be attained when assuming a fairly high value of the real and imaginary parts of the refractive index along the void-fraction curve and a mass density not exceeding 1.5-1.7 g/cm 3 .

show abstract

“…The past three decades have seen increasing interest in black carbon (BC) and elemental carbon (EC), both of which originate from the incomplete combustion of carbonaceous combustibles, due to their strong light-absorbing properties and their possible health effects (Johnson and Huntzicker 1979;Wolff 1981;Turco et al 1983;Molnar et al 1999;Jacobson 2000Jacobson , 2001Ramanathan and Carmichael 2008;Allen et al 2012). EC represents thermally refractory carbon with a graphitic structure, whereas BC is commonly used to define the extent to which an aerosol sample exhibits light-absorbing properties (Salako et al 2012;Gray and Cass 1998;Huntzicker et al 1982;Watson et al 2005).…”

Section: Introductionmentioning

confidence: 99%

Comparison of elemental and black carbon measurements during normal and heavy haze periods: implications for research

Zhi

Chen

Xue

et al. 2014

Environ Monit Assess

View full text Add to dashboard Cite

Studies specifically addressing the elemental carbon (EC)/black carbon (BC) relationship during the transition from clean-normal (CN) air quality to heavy haze (HH) are rare but have important health and climate implications. The present study, in which EC levels are measured using a thermal-optical method and BC levels are measured using an optical method (aethalometer), provides a preliminary insight into this issue. The average daily EC concentration was 3.08±1.10 μg/m 3 during the CN stage but climbed to 11.77±2.01 μg/m 3 during the HH stage. More importantly, the BC/EC ratio averaged 0.92±0.14 during the CN state and increased to 1.88± 0.30 during the HH state. This significant increase in BC/ EC ratio has been confirmed to result partially from an increase in the in situ light absorption efficiency (σ ap ) due to an enhanced internal mixing of the EC with other species. However, the exact enhancement of σ ap was unavailable because our monitoring scheme could not acquire the in situ absorption (b ap ) essential for σ ap calculation. This reveals a need to perform simultaneous measurement of EC and b ap over a time period that includes both the CN and HH stages. In addition, the sensitivity of EC to both anthropogenic emissions and HH conditions implies a need to systematically study how to include EC complex (EC concentration, OC/EC ratio, and σ ap ) as an indicator in air quality observations, in alert systems that assess air quality, and in the governance of emissions and human behaviors.

show abstract

A physically‐based treatment of elemental carbon optics: Implications for global direct forcing of aerosols

Cited by 498 publications

References 39 publications

Saharan dust events at the Jungfraujoch: detection by wavelength dependence of the single scattering albedo and first climatology analysis

Saharan dust events at the Jungfraujoch: detection by wavelength dependence of the single scattering albedo and first climatology analysis

On the Discrepancy between Modeled and Measured Mass Absorption Cross Sections of Light Absorbing Carbon Aerosols

Comparison of elemental and black carbon measurements during normal and heavy haze periods: implications for research

Contact Info

Product

Resources

About