supplementary information - institute of...
TRANSCRIPT
1
Supplementary Information
Krishnakant Budhavant,1 August Andersson,2 Carme Bosch,2 Martin Kruså,2 E. N. Kirillova,2
R. J. Sheesley,2,4 P. D. Safai,3 P. S. P. Rao,3 and Örjan Gustafsson2,5
1 Maldives Climate Observatory at Hanimaadhoo (MCOH), H. Dh. Hanimaadhoo, 02020,
Republic of the Maldives. Email: [email protected]
2 Department of Environmental Science and Analytical Chemistry (ACES) and the Bolin
Centre for Climate Research, Stockholm University, 10691 Stockholm, Sweden
August Andersson, Email: [email protected]
Carme Bosch, Email: [email protected]
Martin Kruså, Email: [email protected]
E. N. Kirillova, Email: [email protected]
3 Indian Institute of Tropical Meteorology, Pashan, Pune 411008, Maharashtra, India.
P. D. Safai, Email: [email protected]
P. S. P. Rao, Email: [email protected]
4 Current affiliation: Department of Environmental Science, Baylor University, Waco, Texas,
USA. Email: [email protected]
5 Corresponding author:
Örjan Gustafsson
Stockholm University, Department of Environmental Science and Analytical Chemistry
(ACES) and the Bolin Centre for Climate Research, 106 91 Stockholm, Sweden, Email:
Short title: 14C of EC aerosols in S Asian receptors
2
Table S1: Results of radiocarbon measurements of EC with measurement errors.
Start date Stop date
F Modern
(blank corr) Fm Err D14C fbiomass
Sinhagad (SINH)
14-Jan-08 29-Jan-08 0.662 0.003 -342.5 0.548
05-Feb-08 26-Feb-08 0.715 0.003 -290.5 0.592
04-Mar-08 25-Mar-08 0.679 0.003 -326.2 0.562
01-Apr-08 29-Apr-08 0.680 0.002 -324.9 0.563
07-May-08 24-Jun-08 0.623 0.002 -381.0 0.516
03-Jul-08 22-Aug-08 0.550 0.003 -454.1 0.455
31-Aug-08 25-Sep-08 0.377 0.002 -625.9 0.312
07-Oct-08 31-Oct-08 0.674 0.004 -330.8 0.558
11-Nov-08 18-Dec-08 0.568 0.004 -436.0 0.470
30-Dec-08 22-Jan-09 0.622 0.004 -382.4 0.515
22-Jan-09 25-Feb-09 0.700 0.004 -304.8 0.580
04-Mar-09 22-Apr-09 0.561 0.004 -442.8 0.465
Maldives Climate Observatory at Hanimaadhoo (MCOH)
15-Jan-08 6-Feb-08 0.692 0.003 -313.2 0.573
6-Feb-08 4-Mar-08 0.698 0.004 -306.6 0.578
4-Mar-08 3-Apr-08 0.675 0.002 -329.5 0.559
3-Apr-08 1-May-08 0.546 0.002 -457.4 0.453
1-May-08 19-Jun-08 0.775 0.002 -230.4 0.642
19-Jun-08 3-Sep-08 0.751 0.003 -254.8 0.622
3-Sep-08 30-Oct-08 0.578 0.002 -425.9 0.479
1-Nov-08 7-Dec-08 0.436 0.002 -566.8 0.361
8-Dec-08 30-Dec-08 0.567 0.002 -436.6 0.470
30-Dec-08 1-Feb-09 0.573 0.003 -430.9 0.475
1-Feb-09 26-Feb-09 0.622 0.002 -382.7 0.515
26-Feb-09 13-Apr-09 0.716 0.003 -288.7 0.593
3
Supplementary Information Text. S1. Sensitivity analysis of EC isolation. During
isolation of EC using the TOT program a potential artifact is incomplete removal, and thus
inadvertent inclusion, of some of the pyrolyzed carbon (PyrC) that may form from the OC
during the initial He atmosphere phase. The formation, and subsequent oxidative removal, of
PyrC is a well-recognized process that is inherent to the design of the method and has been
investigated extensively (e.g., Hammes et al., 2007; Birch and Cary, 1996). Commercially
available TOT instruments, such as the herein employed Sunset Instrument, account for the
PyrC by on-line monitoring of the laser transmission signal through the filter. The creation of
PyrC blackens the filter, reducing the laser transmission. When entering subsequent program
stages, with a higher oxygen mixing ratio, the method is designed to burn off the PyrC.
The split between PyrC and EC is defined as the point where the laser transmission returns
to the value it had at start before any PyrC was formed. This correction is thus introduced to
provide correct estimates of the amounts of EC. It is implicit and assumed that it is the same
material that is being pyrolyzed that then is burned off. However, it is conceivable that this
process may also introduce a certain amount of mixing of carbon from different sources, such
that some ‘ambient’ EC is burned off as PyrC, and that some PyrC is included in the observed
EC fraction. For concentration estimates this potential mixing is not expected to have a large
interference, since the mass absorption cross section for PyrC and EC are assumed to be
similar. However, for isotopic measurements the observed isotopic signature of EC may be
influenced by the isotopic signature of PyrC, which is expected to be similar to the Water-
Soluble OC (WSOC) from which it is formed.
To explore any putative effects of such hypothetical exchange between PyrC/WSOC and
‘ambient’ EC, a sensitivity analysis was carried out on the samples collected during the 2008-
2009 campaigns at MCOH and SINH. To this end, the following equation was used:
4
Δ14CEC,x = [(Δ14CEC)obs [EC]obs –x [EC]obs (Δ14CWSOC)] / ([EC]obs – x [EC]obs)
Where
ECobs observed concentration EC
x fraction of isolated EC that is hypothetically (i.e., tested to be) from pyrolyzed WSOC
Δ14CEC,x the 14C content in an EC isolate with x fraction (0-25%) of the total EC
replaced/exchanged by pyrogenic WSOC
Δ14CWSOC The 14C content of WSOC from the same campaign isolate as reported earlier in
Kirillova et al. (2013)
In this model the biomass combustion fraction (fbio) for PyrC is assumed to be equal to the
biomass combustion fraction of WSOC, which has been reported for the same samples in
Kirillova et al. (2013). The Δ14C data was then converted to fbio following equation 1. For this
sensitivity test, we were able to locate all the necessary instrument-specific information (e.g.,
PyrC – normally not reported or interpreted) for 10 out of 12 MCOH samples and 9 out of 12
SINH samples. For these MCOH and SINH campaign samples, the mean (fbio)WSOC was 0.80
and 0.71, respectively.
The effect on the estimated fbio on maximum “ambient” EC of including 0 - 25% of the PyrC
(as WSOC) in place of the “ambient” EC was calculated from this isotopic mass balance
criterion (Table S2, below). This sensitivity analysis clearly demonstrates that the effects of
including even a large portion of the EC as exchanged PyrC (up to 25%), on the computed fbio
is within the uncertainty range of EC (Table S2). Furthermore, the direction of any such effect
is such that any “correction” would further decrease the estimated fbio of “ambient” EC in the
air over S. Asia above the current estimates, yielding an even larger offset between 14C-EC
top-down source apportionment and the bottom-up EI estimates and thus act to strengthen the
conclusion of this study. This result shows that the current estimates of fbio for EC and
5
associated conclusions are likely to be robust with respect to potential interference from
inadvertent inclusion of instrument-induced PyrC.
Table S2. Sensitivity analysis of putative inadvertent inclusion of instrument-pyrolyzed
carbon (PyrC as WSOC) in the EC isolate for the computed biomass combustion fraction (fbio)
of the “ambient” EC for the tested 2008-2009 MCOH and SINH campaigns samples
Fraction of PyrC in
the EC isolate (%)
MCOH SINH
“ambient” EC fbio
(%)
1 SD (%) “ambient” EC fbio
(%)
1 SD (%)
0 52 9 49 8
5 50 9 48 8
10 49 9 47 9
15 47 10 45 9
20 45 10 44 10
25 42 11 42 10
6
Figure S1: Monthly MODIS active fires composite during January to December, 2008