Scavenging of black carbon by ice crystals over the northern Pacific

Baumgardner, D.; Subramanian, R.; Twohy, Cynthia H.; Stith, Jeffrey L.; Kok, Gregory L.

doi:10.1029/2008gl035764

Cited by 44 publications

(44 citation statements)

References 19 publications

(23 reference statements)

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“…Our results differ in that collisions are shown to dominate over nucleation or freezing for transfer of aerosol into the ice crystals. This is in agreement with recent work by Baumgardner et al (2008), who suggested that impaction scavenging might dominate over nucleation scavenging for black carbon scavenging into ice crystals. Our study also implemented the below-cloud scavenging parameterization of Croft et al (2009), which accounts for the higher aerosol removal by below-cloud scavenging in comparison to the results in Fig.…”

Section: In-cloud Scavenging Sensitivity Simulationssupporting

confidence: 82%

See 1 more Smart Citation

Influences of in-cloud aerosol scavenging parameterizations on aerosol concentrations and wet deposition in ECHAM5-HAM

et al. 2010

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Abstract.A diagnostic cloud nucleation scavenging scheme, which determines stratiform cloud scavenging ratios for both aerosol mass and number distributions, based on cloud droplet, and ice crystal number concentrations, is introduced into the ECHAM5-HAM global climate model. This scheme is coupled with a size-dependent in-cloud impaction scavenging parameterization for both cloud droplet-aerosol, and ice crystal-aerosol collisions. The aerosol mass scavenged in stratiform clouds is found to be primarily (>90%) scavenged by cloud nucleation processes for all aerosol species, except for dust (50%). The aerosol number scavenged is primarily (>90%) attributed to impaction. 99% of this impaction scavenging occurs in clouds with temperatures less than 273 K. Sensitivity studies are presented, which compare aerosol concentrations, burdens, and deposition for a variety of incloud scavenging approaches: prescribed fractions, a more computationally expensive prognostic aerosol cloud processing treatment, and the new diagnostic scheme, also with modified assumptions about in-cloud impaction and nucleation scavenging. Our results show that while uncertainties in the representation of in-cloud scavenging processes can lead to differences in the range of 20-30% for the predicted annual, global mean aerosol mass burdens, and near to 50% for accumulation mode aerosol number burden, the differences in predicted aerosol mass concentrations can be up to Correspondence to: B. Croft (croft@mathstat.dal.ca) one order of magnitude, particularly for regions of the middle troposphere with temperatures below 273 K where mixed and ice phase clouds exist. Different parameterizations for impaction scavenging changed the predicted global, annual mean number removal attributed to ice clouds by seven-fold, and the global, annual dust mass removal attributed to impaction by two orders of magnitude. Closer agreement with observations of black carbon profiles from aircraft (increases near to one order of magnitude for mixed phase clouds), midtroposphere 210 Pb vertical profiles, and the geographic distribution of aerosol optical depth is found for the new diagnostic scavenging scheme compared to the prescribed scavenging fraction scheme of the standard ECHAM5-HAM. The diagnostic and prognostic schemes represent the variability of scavenged fractions particularly for submicron size aerosols, and for mixed and ice phase clouds, and are recommended in preference to the prescribed scavenging fractions method.

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Section: In-cloud Scavenging Sensitivity Simulationssupporting

confidence: 82%

“…Jacobson (2003) found for a one-dimensional study that aerosol mass was primarily scavenged by nucleation, whereas aerosol number was primarily scavenged by impaction processes. Recently, Baumgardner et al (2008) have suggested that for black carbon, scavenging by ice crystals is dominated by impaction as opposed to nucleation processes.…”

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confidence: 99%

Influences of in-cloud aerosol scavenging parameterizations on aerosol concentrations and wet deposition in ECHAM5-HAM

et al. 2010

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“…The findings from this study agree with those of and show that during periods of precipitation, BC exhibited a slightly lower degree of mixing (36 ± 14% thickly coated), possibly implying an enhanced scavenging due to the mixing with volatile/semi-volatile materials. However, rather than nucleation scavenging, the inertial scavenging of BC could play a more significant role when incorporated into ice particles of cirrus (Baumgardner et al, 2008), and the impaction with hydrometeor may also be an important contributor to BC removal by precipitation (Jacobson, 2004). More work is necessary to investigate the role of particle inertia and different mechanisms for BC to be nucleation activated as IN.…”

Section: Discussionmentioning

confidence: 99%

Single particle characterization of black carbon aerosols at a tropospheric alpine site in Switzerland

et al. 2010

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Abstract.The refractory black carbon (rBC) mass, size distribution (190-720 nm) and mixing state in submicron aerosols were characterized from late February to March 2007 using a single particle incandescence method at the high alpine research station Jungfraujoch (JFJ), Switzerland (46.33 • N, 7.59 • E, 3580 m a.s.l.). JFJ is a ground based location, which is at times exposed to continental free tropospheric air. A median mass absorption coefficient (MAC) of 10.2 ± 3.2 m 2 g −1 at λ = 630 nm was derived by comparing single particle incandescence measurements of black carbon mass with continuous measurements of absorption coefficient. This value is comparable with other estimates at this location. The aerosols measured at the site were mostly well mixed and aged during transportation via the free troposphere. Pollutant sources were traced by air mass back trajectories, trace gases concentrations and the mass loading of rBC. In southeasterly wind directions, mixed or convective weather types provided the potential to vent polluted boundary layer air from the southern Alpine area and industrial northern Italy, delivering enhanced rBC mass loading and CN concentrations to the JFJ. The aerosol loadings at this site were also significantly influenced by precipitation, which led to the removal of rBC from the atmosphere. Precipitation events were shown to remove about 65% of the rBC mass from the free tropospheric background reducing the mean loading from 13 ± 5 ng m −3 to 6± 2 ng m −3 (corrected Correspondence to: D. Liu (dantong.liu@postgrad.manchester.ac.uk) to standard temperature and pressure). Overall, 40± 15% of the observed rBC particles within the detectable size range were mixed with large amounts of non-refractory materials present as a thick coating. The growth of particle size into the accumulation mode was positively linked with the degree of rBC mixing, suggesting the important role of condensable materials in increasing particle size and leading to enhanced internal mixing of these materials with rBC. It is the first time that BC mass, size distribution and mixing state are reported in the free troposphere over Europe. These ground based measurements also provide the first temporal study of rBC in the European free troposphere quantitatively measured by single particle methods. At the present time there is only limited information of BC and its mixing state in the free troposphere, especially above Europe. The results reported in this paper provide an important constraint on modelled representation of BC.

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“…In the case of cold clouds (T < 258 K), we assume that only dust and hydrophobic BC can serve as IN and hence be removed by scavenging (Chen et al, 1998;Andreae and Rosenfeld, 2008). Cozic et al (2007) find that the BC fraction scavenged into cloud droplets decreases with decreasing temperature, from 60 % at 0 • C to 10 % at < −20 • C. However, it must be recognized that the scavenging of BC by cold clouds is highly uncertain (Karcher et al, 2007;Baumgardner et al, 2008;Cozic et al, 2008;Targino et al, 2009;Stith et al, 2011).…”

Section: Wet Depositionmentioning

confidence: 99%

Sources of carbonaceous aerosols and deposited black carbon in the Arctic in winter-spring: implications for radiative forcing

et al. 2011

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Abstract. We use a global chemical transport model (GEOSChem CTM) to interpret observations of black carbon (BC) and organic aerosol (OA) from the NASA ARCTAS aircraft campaign over the North American Arctic in April 2008, as well as longer-term records in surface air and in snow (2007)(2008)(2009). BC emission inventories for North America, Europe, and Asia in the model are tested by comparison with surface air observations over these source regions. Russian open fires were the dominant source of OA in the Arctic troposphere during ARCTAS but we find that BC was of prevailingly anthropogenic (fossil fuel and biofuel) origin, particularly in surface air. This source attribution is confirmed by correlation of BC and OA with acetonitrile and sulfate in the model and in the observations. Asian emissions are the main anthropogenic source of BC in the free troposphere but European, Russian and North American sources are also important in surface air. Russian anthropogenic emissions appear to dominate the source of BC in Arctic surface air in winter. Model simulations for 2007-2009 (to account for interannual variability of fires) show much higher BC snow content in the Eurasian than the North American Arctic, consistent with the limited observations. We find that anthropogenic sourcesCorrespondence to: Q. Wang (wang2@fas.harvard.edu) contribute 90 % of BC deposited to Arctic snow in JanuaryMarch and 60 % in April-May 2007-2009. The mean decrease in Arctic snow albedo from BC deposition is estimated to be 0.6 % in spring, resulting in a regional surface radiative forcing consistent with previous estimates.

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Scavenging of black carbon by ice crystals over the northern Pacific

Cited by 44 publications

References 19 publications

Influences of in-cloud aerosol scavenging parameterizations on aerosol concentrations and wet deposition in ECHAM5-HAM

Influences of in-cloud aerosol scavenging parameterizations on aerosol concentrations and wet deposition in ECHAM5-HAM

Single particle characterization of black carbon aerosols at a tropospheric alpine site in Switzerland

Sources of carbonaceous aerosols and deposited black carbon in the Arctic in winter-spring: implications for radiative forcing

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