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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: kbbudhavant@gmail.com

2 Department of Environmental Science and Analytical Chemistry (ACES) and the Bolin

Centre for Climate Research, Stockholm University, 10691 Stockholm, Sweden

August Andersson, Email: august.andersson@aces.su.se

Carme Bosch, Email: carme.bosch@aces.su.se

Martin Kruså, Email: martin.krusa@aces.su.se

E. N. Kirillova, Email: elena-nk@hotmail.com

3 Indian Institute of Tropical Meteorology, Pashan, Pune 411008, Maharashtra, India.

P. D. Safai, Email: pdsafai@tropmet.res.in

P. S. P. Rao, Email: psprao@tropmet.res.in

4 Current affiliation: Department of Environmental Science, Baylor University, Waco, Texas,

USA. Email: Rebecca_Sheesley@baylor.edu

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:

orjan.gustafsson@aces.su.se

Short title: 14C of EC aerosols in S Asian receptors

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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

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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:

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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

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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

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Figure S1: Monthly MODIS active fires composite during January to December, 2008