Estimates of mass absorption cross sections of black carbon for filter-based absorption photometers in the Arctic
Long-term measurements of atmospheric mass concentrations of black carbon (BC) are needed to investigate changes in its emission, transport, and deposition. However, depending on instrumentation, parameters related to BC such as aerosol absorption coefficient (babs) have been measured instead. Most...
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Published in | Atmospheric measurement techniques Vol. 14; no. 10; pp. 6723 - 6748 |
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Main Authors | , , , , , , , , , , , , , , , , , , , , , , |
Format | Journal Article |
Language | English |
Published |
Katlenburg-Lindau
Copernicus GmbH
20.10.2021
Copernicus Publications |
Subjects | |
Online Access | Get full text |
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Summary: | Long-term measurements of atmospheric mass concentrations
of black carbon (BC) are needed to investigate changes in its emission,
transport, and deposition. However, depending on instrumentation, parameters
related to BC such as aerosol absorption coefficient (babs) have been
measured instead. Most ground-based measurements of babs in the Arctic
have been made by filter-based absorption photometers, including particle
soot absorption photometers (PSAPs), continuous light absorption photometers
(CLAPs), Aethalometers, and multi-angle absorption photometers (MAAPs). The
measured babs can be converted to mass concentrations of BC (MBC) by
assuming the value of the mass absorption cross section (MAC; MBC= babs/ MAC). However, the accuracy of conversion of babs to MBC
has not been adequately assessed. Here, we introduce a systematic method for
deriving MAC values from babs measured by these instruments and
independently measured MBC. In this method, MBC was measured with a
filter-based absorption photometer with a heated inlet (COSMOS).
COSMOS-derived MBC (MBC (COSMOS)) is traceable to a rigorously
calibrated single particle soot photometer (SP2), and the absolute accuracy
of MBC (COSMOS) has been demonstrated previously to be about 15 % in
Asia and the Arctic. The necessary conditions for application of this method
are a high correlation of the measured babs with independently measured
MBC and long-term stability of the regression slope, which is denoted
as MACcor (MAC derived from the correlation). In general,
babs–MBC (COSMOS) correlations were high (r2= 0.76–0.95 for
hourly data) at Alert in Canada, Ny-Ålesund in Svalbard, Barrow (NOAA Barrow Observatory) in
Alaska, Pallastunturi in Finland, and Fukue in Japan and stable for up to
10 years. We successfully estimated MACcor values (10.8–15.1 m2 g−1 at a wavelength of 550 nm for hourly data) for these instruments,
and these MACcor values can be used to obtain error-constrained
estimates of MBC from babs measured at these sites even in the past,
when COSMOS measurements were not made. Because the absolute values of
MBC at these Arctic sites estimated by this method are consistent with
each other, they are applicable to the study of spatial and temporal
variation in MBC in the Arctic and to evaluation of the performance of
numerical model calculations. |
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ISSN: | 1867-8548 1867-1381 1867-8548 |
DOI: | 10.5194/amt-14-6723-2021 |