Please use this identifier to cite or link to this item: http://hdl.handle.net/2381/32620
Title: Size distribution, mixing state and source apportionment of black carbon aerosol in London during wintertime
Authors: Liu, D.
Allan, J. D.
Young, D. E.
Coe, H.
Beddows, D.
Fleming, Zoe L.
Flynn, M. J.
Gallagher, M. .W.
Harrison, R. M.
Lee, J.
Prevot, A. S. H.
Taylor, J. W.
Yin, J.
Williams, P. I.
Zotter, P.
First Published: 22-Sep-2014
Publisher: Copernicus Publications on behalf of the European Geosciences Union
Citation: Atmospheric Chemistry and Physics, 2014, 14 (18), pp. 10061-10084
Abstract: Black carbon aerosols (BC) at a London urban site were characterised in both winter- and summertime 2012 during the Clean Air for London (ClearfLo) project. Positive matrix factorisation (PMF) factors of organic aerosol mass spectra measured by a high-resolution aerosol mass spectrometer (HR-AMS) showed traffic-dominant sources in summer but in winter the influence of additional non-traffic sources became more important, mainly from solid fuel sources (SF). Measurements using a single particle soot photometer (SP2, DMT), showed the traffic-dominant BC exhibited an almost uniform BC core size (D[subscript: c]) distribution with very thin coating thickness throughout the detectable range of D[subscript: c]. However, the size distribution of D[subscript: c] (project average mass median D[subscript: c] = 149 ± 22 nm in winter, and 120 ± 6 nm in summer) and BC coating thickness varied significantly in winter. A novel methodology was developed to attribute the BC number concentrations and mass abundances from traffic (BC[subscript: tr]) and from SF (BC[subscript: sf]), by using a 2-D histogram of the particle optical properties as a function of BC core size, as measured by the SP2. The BC[subscript: tr] and BC[subscript: sf] showed distinctly different D[subscript: c] distributions and coating thicknesses, with BC[subscript: sf] displaying larger D[subscript: c] and larger coating thickness compared to BC[subscript: tr]. BC particles from different sources were also apportioned by applying a multiple linear regression between the total BC mass and each AMS-PMF factor (BC–AMS–PMF method), and also attributed by applying the absorption spectral dependence of carbonaceous aerosols to 7-wavelength Aethalometer measurements (Aethalometer method). Air masses that originated from westerly (W), southeasterly (SE), and easterly (E) sectors showed BC[subscript: sf] fractions that ranged from low to high, and whose mass median D[subscript: c] values were 137 ± 10 nm, 143 ± 11 nm and 169 ± 29 nm, respectively. The corresponding bulk relative coating thickness of BC (coated particle size/BC core – D[subscript: p]/D[subscript: c]) for these same sectors was 1.28 ± 0.07, 1.45 ± 0.16 and 1.65 ± 0.19. For W, SE and E air masses, the number fraction of BCsf ranged from 6 ± 2% to 11 ± 5% to 18 ± 10%, respectively, but importantly the larger BC core sizes lead to an increased fraction of BCsf in terms of mass than number (for W, SE and E air masses, the BCsf mass fractions ranged from 16 ± 6%, 24 ± 10% and 39 ± 14%, respectively). An increased fraction of non-BC particles (particles that did not contain a BC core) was also observed when SF sources were more significant. The BC mass attribution by the SP2 method agreed well with the BC–AMS–PMF multiple linear regression method (BC–AMS–PMF : SP2 ratio = 1.05, r[superscript: 2) = 0.80) over the entire experimental period. Good agreement was found between BCsf attributed with the Aethalometer model and the SP2. However, the assumed absorption Ångström exponent (α[subscript: wb]) had to be changed according to the different air mass sectors to yield the best comparison with the SP2. This could be due to influences of fuel type or burn phase.
DOI Link: 10.5194/acp-14-10061-2014
ISSN: 1680-7316
eISSN: 1680-7324
Links: http://www.atmos-chem-phys.net/14/10061/2014/acp-14-10061-2014.html
http://hdl.handle.net/2381/32620
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: Copyright © the authors, 2014. This is an open-access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/3.0/ ), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Appears in Collections:Published Articles, Dept. of Chemistry

Files in This Item:
File Description SizeFormat 
acp-14-10061-2014.pdfPublished (publisher PDF)2.74 MBAdobe PDFView/Open


Items in LRA are protected by copyright, with all rights reserved, unless otherwise indicated.