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| Titel |
Size distribution, mixing state and source apportionment of black carbon aerosol in London during wintertime |
| VerfasserIn |
D. Liu, J. D. Allan, D. E. Young, H. Coe, D. Beddows, Z. L. Fleming, M. J. Flynn, M. W. Gallagher, R. M. Harrison, J. Lee, A. S. H. Prévôt, J. W. Taylor, J. Yin, P. I. Williams, P. Zotter |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 14, no. 18 ; Nr. 14, no. 18 (2014-09-22), S.10061-10084 |
| Datensatznummer |
250119056
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| Publikation (Nr.) |
 copernicus.org/acp-14-10061-2014.pdf |
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| Zusammenfassung |
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 (Dc) distribution with very thin coating thickness throughout the
detectable range of Dc. However, the size distribution of Dc
(project average mass median Dc = 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 (BCtr) and from SF
(BCsf), by using a 2-D histogram of the particle optical properties as
a function of BC core size, as measured by the SP2. The BCtr and
BCsf showed distinctly different Dc distributions and coating
thicknesses, with BCsf displaying larger Dc and larger coating
thickness compared to BCtr. 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 BCsf fractions that ranged from low to
high, and whose mass median Dc 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 – Dp/Dc) 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, r2 = 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
(αwb) 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. |
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