Environ. Sci. Technol. 2009, 43, 8233–8239
Absorption Coefficient and
Site-Specific Mass Absorption
Efficiency of Elemental Carbon in
Aerosols over Urban, Rural, and
High-Altitude Sites in India
KIRPA RAM AND M. M. SARIN*
Physical Research Laboratory, Ahmedabad - 380 009, India
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Publication Date (Web): September 28, 2009 | doi: 10.1021/es9011542
Received April 17, 2009. Revised manuscript received
September 3, 2009. Accepted September 10, 2009.
Temporal and spatial variability in the absorption coefficient
(babs, Mm-1) and mass absorption efficiency (MAE, σabs, m2g-1)
of elemental carbon (EC) in atmospheric aerosols studied
from urban, rural, and high-altitude sites is reported here.
Ambient aerosols, collected on tissuquartz filters, are analyzed
for EC mass concentration using thermo-optical EC-OC
analyzer, wherein simultaneously measured optical-attenuation
(ATN, equivalent to initial transmittance) of 678 nm laser
source has been used for the determination of MAE and
absorption coefficient. At high-altitude sites, measured ATN
and surface EC loading (ECs, µg cm-2) on the filters exhibit linear
positive relationship (R2 ) 0.86-0.96), suggesting EC as a
principal absorbing component. However, relatively large scatter
in regression analyses for the data from urban sites suggests
contribution from other species. The representative MAE of
EC, during wintertime (Dec 2004), at a rural site (Jaduguda) is
6.1 ( 2.0 m2g-1. In contrast, MAE at the two high-altitude
sites is 14.5 ( 1.1 (Manora Peak) and 10.4 ( 1.4 (Mt. Abu);
and that at urban sites is 11.1 ( 2.6 (Allahabad) and 11.3 ( 2.2
m2g-1 (Hisar). The long-term average MAE at Manora Peak
(February 2005 to June 2007) is 12.8 ( 2.9 m2g-1 (range: 6.1-19.1
m2g-1). These results are unlike the constant conversion
factor used for MAE in optical instruments for the determination
of BC mass concentration. The absorption coefficient also
shows large spatiotemporal variability; the lower values are
typical of the high-altitude sites and higher values for the urban
and rural atmosphere. Such large variability documented for
the absorption parameters suggests the need for their suitable
parametrization in the assessment of direct aerosol radiative
forcing on a regional scale.
1. Introduction
Black carbon (BC), produced during incomplete fossil-fuel
and biomass combustion processes, is one of the major
absorbing particulate species in the atmosphere and is being
considered as a driver of the global warming (1, 2). The
absorption and scattering properties of aerosols are the key
parameters to assess direct aerosol radiative forcing and their
climatic impact on a regional to global scale (3-5). The
absorption coefficient (babs) is either measured using photoacoustic instruments (6, 7) or more commonly used online
* Corresponding author phone: +91 79 26314306; fax: +91 79
26301502; e-mail: [email protected].
10.1021/es9011542 CCC: $40.75
Published on Web 09/28/2009
 2009 American Chemical Society
filter-based absorption methods (8-12); whereas scattering
coefficient (bscat) is mainly inferred from Nephelometer based
measurements (11, 12). Nevertheless, the assessment of
radiative forcing is associated with large uncertainty arising
due to the lack of reliable measurements of these optical
parameters (13). The filter-based online absorption measurements are affected by the shadowing and multiple
scattering effects (8, 9, 11-13). Also, relevant information on
the mixing state of BC in aerosols is essential as the internal
mixing leads to further increase in absorption signal
(2, 10, 14-16).
The measurement of BC mass concentration via optical
methods is relatively convenient and rapid but requires
knowledge of “site-specific” mass absorption efficiency (MAE
or σabs). A wide range of values for σabs (2-25 m2g-1) have
been reported in the literature, derived based on independent
and simultaneous measurements of EC concentration (by
thermal method) and absorption coefficient by optical
methods (9, 10, 15, 16). The variability in MAE has been
interpreted in terms of source regions, analytical measurement protocols, chemical and optical properties of aerosols
at a sampling site (13, 14). Furthermore, aging and atmospheric chemical processing can lead to an internal mixing
of BC in aerosols, and thus, increases the MAE through
enhancement in absorption signal for the same amount of
BC (13, 15). The use of site-specific σabs for the determination
of BC mass concentration by optical methods has been
suggested (13, 14). However, it is common practice to use a
constant value of σabs at a given wavelength. For example,
the Aethalometer uses a value of 16.6 m2g-1 (at 880 nm) while
particle soot absorption photometer (PSAP) uses a value of
10 m2g-1 to convert measured absorption into BC mass
concentration (10). A recent review by Bond and Bergstrom
(9) has suggested a value of 7.5 ( 1.2 m2g-1 at 550 nm for σabs
for uncoated soot particles.
Carbonaceous aerosols in south-Asian region, originating
from a variety of anthropogenic sources, are gaining considerable importance because of their potential impact on
regional climate (3-5). In this context, systematic measurements of relevant optical parameters (BC mass fraction, babs,
bscat, and site-specific σabs) from Indian region are essential.
This manuscript reports the first measurement of these
parameters from northern India; documenting large temporal
and spatial variability in σabs and babs over urban, rural, and
high-altitude sites. Our analytical approach makes use of
the optical-attenuation (ATN) measured at 678 nm, on
thermo-optical EC-OC analyzer, for the simultaneous determination of babs and σabs along with the measurement of
EC and OC mass concentrations.
2. Experimental Methods
2.1. Study Sites and Aerosol Sample Collection. Ambient
aerosol samples were collected from urban, rural and highaltitude sites during wintertime (December 2004). Hisar
(29.2°N, 75.7°E) and Allahabad (25.4°N, 81.9°E) are the two
typical urban sites in northern India, mainly influenced by
biomass burning emissions during wintertime. Aerosol
sampling from rural site, Jaduguda (22.5°N, 85.7°E), dominated by coal-based emissions provide an appropriate
location to study their optical and chemical properties. The
locations of sampling sites and prevailing wind pattern
(during wintertime) are shown in Figure 1 and relevant details
are provided in Table 1. The aerosol loading at the two highaltitude sites, Manora Peak (29.4°N, 79.5°E, ∼1950 m above
sea level (asl)) and Mt. Abu (24.6°N, 72.7°E, ∼1700 m asl) are
dominated by the long-range transport as well as local
VOL. 43, NO. 21, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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measurement is no more than 7% (except in few cases where
it is as high as 13%) and is expressed as relative percentage
deviation from n ) 20 measurements. The relevant parameters used in this study, along with the associated measurement errors, have been summarized in Supporting Information (SI) Section A1 and Table S1.
The measurement of ATN and methodology used in this
study are similar to those employed in filter-based online
optical instruments (8, 12). In the latter approach, aerosols
are generally collected for a short time on a small filter area
at low flow rates and ATN is obtained by measuring the
change in transmittance as a function of time. On the
contrary, collection of aerosol samples integrated over longer
time on a large filter area (as used in this study) minimizes
the sample heterogeneity and enhances the ATN signal. The
attenuation cross-section (σATN, m2g-1) can be directly
obtained from above eq 1 by correcting the measured ATN
for shadowing effect (R(ATN); as explained in later section)
and dividing by surface EC loading (ECs):
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σATN(m2g-1) )
FIGURE 1. The typical wind pattern (@10 ms-1) during
wintertime (December 2004) at the sampling locations
Allahabad and Hisar (urban sites), Mt. Abu and Manora Peak
(high-altitude sites) and Jaduguda (rural site).
emission sources (17, 18). In addition, an extended sampling
was carried out at the two high-altitude sites (Manora Peak:
February 2005 to June 2007, Mt. Abu: May 2005 to February
2006). All samples were collected by operating a high-volume
sampler at a flow rate of ∼1.0 m3 min-1 and using precombusted (at 500 °C for ∼6 h) tissuquartz filters (Pallflex, 2500
QAT-UP; size: 20 × 25 cm2), integrated for ∼15-20 h in order
to meet the analytical requirements for the determination of
carbonaceous species and a suit of chemical constituents
(17, 18).
2.2. Thermal EC and Optical-Attenuation (ATN) Measurements. Sample aliquots in the form of punches (1.5 cm2)
were drawn from main filters and surface EC loading (ECs;
in unit of µg cm-2) was ascertained on the EC-OC analyzer
(Sunset Laboratory, Forest Grove, OR) using thermal-optical
transmittance (TOT) protocol (19, 20). The temperature
program used in this study is described in our earlier
publication (17, 18) and is similar to the base case temperature
program used in the ACE-Asia intercomparison study (19).
The analytical instrument (EC-OC analyzer) provides absorbance (equivalent to initial transmittance) at 678 nm by
measuring intensities of incident and transmitted light
through the filter loaded with aerosols. The absorption signal
is represented by optical-attenuation (ATN, a unit less
parameter) and is governed by the Beer-Lambert’s law,
according to the following equation:
()
ATN ) -100 · ln
I
I0
(1)
where I0 is the intensity of incident light and I is the
transmitted light through the filter substrate and aerosols.
The measured ATN signal for blank filters is zero (n ) 50).
Thus, the measured ATN through the sample filter is
attributed to the presence of light absorbing carbon (LAC)
and is equivalent to in situ EC concentration in aerosols (15).
Sciare et al. (20) had reported that absorption measurements
performed on PSAP showed good agreement with those
measured from Sunset EC-OC analyzer (R2 ) 0.93). Hence,
simultaneous measurements of ATN and ECs can be used to
determine the absorption coefficient (babs) and mass absorption efficiency of EC (σabs). The uncertainty in the ATN
8234
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 43, NO. 21, 2009
ATN
R(ATN) · ECs
(2)
2.3. Determination of Aerosol Absorption Coefficient
(babs) and Mass Absorption Efficiency of EC (σabs). The
attenuation coefficient (bATN) is calculated from the measured
ATN with the help of following equation:
bATN )
ATN · A(m2)
V(m3)
(3)
whereas absorption coefficient (babs) is related to bATN
according to eq 4 as described in the literature (8, 11-13)
babs )
bATN
ATN
A
· )
C · R(ATN) V
C · R(ATN)
(4)
where, A is the effective filter area (417 × 10-4 m2 for
tissuquartz filter used in this study), V is the volume of air
sampled (m3). C and R(ATN) are the two empirical factors
for correcting the measured absorption due to the multiple
scattering and shadowing effects, respectively. The value of
C depends on the type of absorbing material, the filter
substrate and mixing state of BC in aerosols (8, 9). A value
of 2.14 ( 0.21 has been suggested for correction due to the
multiple scattering effect for uncoated and externally mixed
soot particles collected on tissuquartz filters (same as used
in present study) (8, 9). However, much higher values have
been reported for internally mixed aerosol particles (e.g., 3.6
( 0.6 for soot particles coated with organics) (8). This
introduces large uncertainty in babs values when filter-based
measurements are performed. We have used a value of 2.14
( 0.21 for C and R(ATN) has been determined using eq 5.
The multiple scattering effect is due to accumulation of
particles and leads to an enhancement in absorption while
the shadowing effect decreases absorption by reducing the
optical path length. Weingartner et al. (8) have provided a
wavelength dependent parameter f to estimate R(ATN) by
fitting linear empirical curve to the observed data set obtained
by Aethalometer:
R(ATN) )
- ln 10
+1
( 1f - 1)( lnlnATN
50 - ln 10 )
(5)
where R(ATN) depends on parameter f and decreases with
increasing value of f. It is evident from above equation that
for lower values of optical-attenuation (ATN e 10%), R(ATN)
can be taken as unity. However, for ATN > 10%, R(ATN) values
are always less than unity and decreases with increasing ATN.
For ATN > 10%, we have used f ) 1.103 during wintertime
(December-March) and f ) 1.114 for rest of the seasons to
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TABLE 1. Absorption Coefficient (babs) and Site-Specific Mass Absorption Efficiency (σabs) of EC at Different Geographical
Locations in Northern India
longitude
°E
elevation
m asl
σabs (m2g-1)
sampling time
location
type
latitude
°N
December 04
December 04
December 04
December 04
February 05
to June 07
December 05 to
February 06
May 05 to
February 06
Jaduguda
Hisar
Allahabad
Manora Peak
rural
urban
urban
high-altitude
22.5
29.2
25.4
29.4
85.7
75.7
81.9
79.5
150
219
123
2000
7
40
19
20
3.1 ( 0.6
8.5 ( 2.2
8.1 ( 1.7
6.0 ( 1.9
69.7 ( 19.6
39.9 ( 9.1
66.1 ( 17.2
12.9 ( 4.6
6.1 ( 2.0
11.3 ( 2.2
11.1 ( 2.6
14.5 ( 1.1
3.4
6.1
7.5
12.7
9.1
16.4
16.8
16.9
Manora Peak
high-altitude
29.4
79.5
2000
47
8.6 ( 2.8
12.2 ( 6.6
12.8 ( 2.9
6.1
19.1
Mt. Abu
high-altitude
24.6
72.7
1700
14
6.1 ( 2.0
8.0 ( 5.5
10.4 ( 1.4
8.1
12.2
Mt. Abu
high-altitude
24.6
72.7
1700
37
6.1 ( 2.0
5.8 ( 4.3
9.8 ( 2.1
3.6
13.7
calculate R(ATN) from eq 5 as per values reported at 660 nm
(21). It is noteworthy that use of f value equal to 1.103 or
1.114 leads to maximum change of 2% in R(ATN). The
calculated values of 0.85 ( 0.03 for R(ATN) at the sampling
sites (Hisar, Allahabad and Jaduguda) are similar (within
errors) to that used by Chou et al. (22) for an urban site in
Taipei (0.80) wheras R(ATN) is relatively high (0.92 ( 0.04)
for the high-altitude sites. The propagated root-sum-square
error (RSSE) for the determination of aerosol absorption
coefficient (babs) is ∼23%, arising from measurements of
ATN, A, V, and corrections due to the multiple scattering and
shadowing effects.
The attenuation cross-section (σATN) and mass absorption
efficiency (σabs) are the two frequently used terms for
determination of BC mass concentration via optical methods.
Although, both parameters are expressed in same units
(m2g-1); σATN accounts for the intrinsic absorption due to BC
particles and an additional increase in light absorption due
to the multiple scattering effect (C) and is related with σabs
by the following equation:
σabs )
σATN(m2g-1)
babs(Mm-1)
)
C
EC(µgm-3)
(6)
Assuming an uncertainty of ∼23% in babs and 22% in EC
measurements (23), the propagated RSSE in determination
of σabs is estimated to be of the order of ∼32% using our
approach.
3. Results and Discussion
3.1. Optical-Attenuation (ATN) and Thermal EC Concentration. The analytical data on optical-attenuation (ATN),
surface EC loading (ECs; µg cm-2), EC concentration (EC; µg
m-3), absorption coefficient (babs, Mm-1; 1Mm-1 ) 10-6 m-1)
and mass absorption efficiency (MAE, σabs, m2g-1) for the
high-altitude site, Manora Peak, are given in SI Tables S2
and S3. The measured ATN and ECs concentrations at Manora
Peak varied from 8 to 134 and 0.3 to 9.3 µg cm-2 over the
entire sampling period (February 2005 to June 2007); whereas
the two parameters varied from 15 to 95 and 0.5 to 3.5 µg
cm-2, respectively for the daily samples collected during
wintertime (December 2004). The measured ATN and ECs
concentration exhibit a significant linear relationship at
Manora Peak (R2 ) 0.96 and 0.86 respectively in Figures 2a
and b), indicating the validity of Beer-Lambert’s law and EC
as a principal absorbing component in aerosols. However,
this linearity does not extend for ECs exceeding 4.5 µg cm-2.
Recently, Junker et al. (24) have reported that ATN measured
by Aethalometer (range: 22-178) varied linearly with BC
surface mass loading (in unit of µg cm-2). In a related study,
it has been shown that about 90% of data fall in the linear
range for babs <50 Mm-1 and EC <5 µg m-3; but the relationship
becomes nonlinear for higher abundances of EC (25). In this
N
OC/EC
ratio
babs (Mm )
average
min
max
-1
study, measured ATN and babs values at Manora Peak (Max.:
134 and 33.6 Mm-1, respectively) are lower compared to those
reported in the literature (24, 25).
The linear regression analysis between ATN and ECs
concentration at Manora Peak yields a slope of 22.4 m2g-1
and an intercept of 6.6 (R2 ) 0.86, for n ) 39, excluding seven
data points with ECs > 4.5 µg cm-2, Figure 2b). During a field
campaign conducted in Taipei (Taiwan), Chou et al. (26) had
reported a value of 23.7 m2g-1 for the slope and 12.0 for the
intercept with a correlation coefficient (R2) of 0.69. Based on
the absorption measurements from PSAP and Aethalometer,
and thermal EC concentration using Sunset Lab EC-OC
analyzer, Snyder and Schauer (27) have reported σATN values
of 23.7 ( 0.4 m2g-1 at 660 nm (for the Aethalometer) and 18.3
( 0.5 m2g-1 at 565 nm (for PSAP). The slope of the regression
lines (Figure 2) provides a valuable parametersattenuation
cross-section (σATN)swhich in turn has been used to infer
“site-specific” mass absorption efficiency of EC (σabs) (eq 6).
It is noteworthy that intercepts in the linear regression
plots for the two high-altitude sites, Manora Peak (Figures
2a and b) and Mt. Abu (Figures 2c and d), are very small
(approximately one-tenth of the average ATN) and can be
neglected. The near-zero intercept for the data set from these
high-altitude sampling sites suggest EC as principal absorbing
component in aerosols. In contrast, intercepts of regression
plots for two urban locations, Allahabad and Hisar (Figures
2e and f), are 60 and 50 (compared to average ATN: 140 and
130, respectively); statistically very different from zero. The
relatively high intercept in linear regression analyses observed
in case of data from urban sites could be attributed to high
ATN values and high ECs concentration. We suggest that
sampling time can be cut down for collection of aerosol
samples from the highly polluted urban sites. The nonzero
intercept could also be attributed to the presence of absorbing
species other than EC. Mineral dust is another absorbing
species present in aerosols, however, absorption due to
mineral dust is very low compared to that of BC (28). The
aerosol chemical composition at an urban location, Hisar,
indicates equal dominance of both mineral dust and total
carbonaceous aerosols (∼40% of total suspended particulate
(TSP) matter) (17). Assuming that contribution of mineral
dust to TSP is ∼40% and externally mixed with BC; and by
using a value of 0.009 m2g-1 for mass absorption efficiency
of dust (29), its contribution to total absorption is no more
than 2% at Hisar. However, a recent study has documented
a value of 0.03 m2g-1 for mass absorption efficiency of dust
(12) which indicate that absorption from dust can be ∼7%
of total absorption at Hisar.
The lower absorption characteristics of dust is further
supported by relatively nonabsorbing nature of Asian dust
observed during the ACE-Asia campaign (http://www.igac.
noaa.gov/newsletter; Issue No. 28). Also, Carrico et al. (30)
have reported a mean value of 0.94 ( 0.03 for single scattering
VOL. 43, NO. 21, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 2. Linear relationship between optical-attenuation (ATN) and surface EC concentration (ECs, in unit of µg cm-2), indicating
the validity of Beer-Lambert’s law: (a) and (c) data from high-altitude sites during wintertime; (b) and (d) represent extended
sampling at two high-altitude locations; (e) and (f) represent data for the two rural sites in India. The regression parameters m and c
represent slope and intercept of the best-fit line, respectively.
FIGURE 3. Intercomparison of attenuation coefficient derived
from the two different instrumental techniques (EC-OC analyzer
and Aethalometer) indicate good agreement. The regression
parameters m and c represent slope and intercept of the
best-fit line, respectively.
albedo (SSA) for polluted dust air mass during the ACE-Asia
experiment. Organic carbon (OC) mainly scatters the radiation but freshly emitted OC, particularly from biomass
burning emissions having significant amount of brown
8236
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 43, NO. 21, 2009
carbon and humic-like substances (HULIS), can contribute
to total aerosol absorption at a lower wavelength (ultraviolet)
region of the spectrum (1, 12, 31-33). The biomass burning
emissions from wood and agricultural crop-waste dominate
the atmospheric loading of carbonaceous species in India
(5, 18); it is, thus, suggested that freshly emitted OC could
be a potential absorbing component in aerosols at the two
urban sites.
3.2. Intercomparison of Attenuation Coefficient Derived by the EC-OC Analyzer (bATN-ECOC) and the Aethalometer (bATN-Aeth). The BC mass concentrations (µg m-3) at 880
nm, using Aethalometer based measurements during December 2004 campaign (4), have been multiplied by the
attenuation cross-section (16.6 m2g-1) to obtain bATN-Aeth
values and are presented in SI Table S4. Although absorption
coefficient (babs) has been used throughout this paper,
attenuation coefficient (bATN) is more suitable parameter
(independent of C and R(ATN)) for intercomparison of
absorption measurements by the two analytical instruments.
The attenuation coefficient (bATN-ECOC) assessed by the ECOC analyzer at 678 nm has been corrected to 880 nm (using
a value of unity for wavelength dependence of Ångström
exponent) in order to match bATN-Aeth at 880 nm. The
wavelength dependence of bATN is normally assumed to be
a power law where the exponent depends on type of
Six sites across Canada
Six sites across Canada
Fresno supersite, CA
INDOEX
ACE-Asia experiment
Rochester and Philadelphia
ACE-Asia experiment
rural
urban
urban
high-altitude
high-altitude
urban
rural ambient
remote, savannah, suburban
residential, suburban
traffic impacted street
urban
biomass burning emission
free troposphere
artificial BC and rural
diesel emitted
remote, urban, rural
and suburban
urban ambient
biofuel and fossil-fuel emission
polluted aerosol mixed with dust
traffic impacted
marine, pollution and dust mixed
Jaduguda
Hisar
Allahabad
Mt. Abu
Manora Peak
University of Washington
Claremont, CA
France/Western Mediterranean
Munich
Munich
Mainz, Germany
Brazil
Jungfraujoch
Bondville, IL
a
TOT ) thermal optical transmittance. b IPM ) integrating plate method. c TOR ) thermal optical reflectance. d VDI ) verein deutscher ingenieure. e NIOSH ) National Institute for
Occupational Safety and Health. f IMPROVE ) Interagency Monitoring of Protected Visual Environments. g PSAP ) particle soot absorption photometer. h EGA ) evolved gas analysis.
10.8
9
54.8
25
28.3
11.6
12.1 ( 0.7
5.6
3
5.9
5
7
19.3
25.4
6.6
5.2
12.1 ( 4.0
9.3 ( 0.4
6.8
8.5
6.4
3.2
11.4 ( 0.7
8.4
13.7
10.1 ( 0.6
9.8
this study
this study
this study
this study
this study
Edwards, 37
Admas et al., 38
Liousse et al., 16
Petzold and Niessner, 39
Petzold and Niessner, 39
Kuhlbush, 40
Martins et al. (14)
Lavanchy et al., 41
Hitzenberger et al., 42
Moosmuller et al., 43
Sharma et al., 10
Sharma et al., 10
Watson and Chow, 25
Mayol-Bracero et al., 44
Huebert et al., 45
Jeong et al., 46
Quinn et al., 47
9.1
16.4
16.8
12.2
19.1
12
3.4
6.1
7.5
8.1
6.1
7
6.1 ( 2.0
11.3 ( 2.2
11.1 ( 2.6
10.4 ( 1.4
12.8 ( 2.9
sunset
sunset
sunset
sunset
sunset
TORc
TOR
Cachier
VDId
VDI
Cachier
Cachier
Cachier
Cachier/NIOSHe
IMPROVEf TOR
IMPROVE-TOR,
Cachier/NIOSH
IMPROVE-TOR
EGAh
NIOSH
sunset
NIOSH
TOT , sunset
TOT, sunset
TOT, sunset
TOT, sunset
TOT, sunset
IPMb
aethalometer
aethalometer
aethalometer
aethalometer
aethalometer
aethalometer
aethalometer
aethalometer
aethalometer
aethalometer
photoacoustic
aethalometer
PSAPg
PSAP
aethalometer
PSAP
references
max.
average
type
location
a
σabs (m2g-1)
min.
analytical methods
optical
thermal
TABLE 2. Spatiotemporal Variability in Mass Absorption Efficiency (MAE, σabs): Intercomparison with Literature-Based Studies
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absorbing species (bATN R λ-R where R is the Ångström
exponent). The values of the R range from 1 to 3 for
wavelengths between 300 and 1000 nm but an value of unity
have been accepted for Ångström exponent due to light
absorbing carbon (34). The measurement of attenuation
coefficient (bATN) by two independent analytical methods
yields a good correlation (R2 ) 0.82, n ) 24, Figure 3) with
a slope of unity for samples collected at high-altitude site,
Manora Peak; attesting the validity of our approach for bATN
determination.
3.3. Spatial and Temporal Variation of Absorption
Coefficient (babs). The measured ATN at 678 nm has been
used to calculate absorption coefficient (babs) for different
sampling sites in northern India (Table 1). The babs shows a
large spatial and temporal variability, varying by an order of
magnitude, for the entire sampling period and is related to
the difference in chemical and optical characteristics of
carbonaceous species derived from different emission sources
(Table 1). The babs values at Mt. Abu are lower compared to
that at Manora Peak. Among urban sites, babs at Hisar (39.9
( 9.1 Mm-1, n ) 40) is lower compared to Allahabad (66.1
( 17.2 Mm-1, n ) 19) during wintertime (December 2004)
and the highest was observed for rural sampling site,
Jaduguda (69.7 ( 19.6 Mm-1, n ) 7). The EC concentration
at Jaduguda is 11.6 ( 2.0 µg m-3, about a factor of 2 higher
than that at Allahabad (6.2 ( 2.0 µg m-3); whereas OC/EC
ratios are higher at Allahabad compared to that at Jaduguda
(Table 1). These results indicate that emission sources,
chemical, and optical properties of carbonaceous aerosols
are quite different at Allahabad and Jaduguda. Earlier studies
have also documented the dominance of coal-based emissions in the eastern part of India (see site description details
in Section 2.1) (35, 36). Infact, OC/EC ratios at Jaduguda are
lowest among all sampling locations in northern India (Table
1). Thus, relatively low σabs values (6.1 ( 2.1 m2g-1) and high
EC abundance at Jaduguda is, thus, attributed to coal-based
emissions.
The babs at Manora Peak shows a large temporal variability,
ranging from 1.8 to 33.6 Mm-1; with lower values occurring
in summer (April-June) and monsoon season (July-August)
due to relatively low EC content in aerosol. The predominantly higher babs values during postmonsoon (SeptemberNovember) and wintertime (December-March) are attributed to enhanced biomass burning activities resulting in
higher EC abundances (18). The babs at Manora Peak during
wintertime (December 2004) varies from 4.4 to 20.9 Mm-1
with an average value of 12.9 ( 4.6 Mm-1 (n ) 20, 1σ), a
factor of 3 lower than the reported value of 44.6 ( 26.4 Mm-1
(n ) 9) during December 2003 from Taipei by Chou et al.
(22). Although, babs values show a large variability during
February 05 to June 07 sampling period (range: 1.8-33.6
Mm-1), average babs (12.2 ( 6.6 Mm-1, n ) 47) is similar to
that obtained in December 2004 (Table 1). The optical
parameters vary on temporal as well as on spatial scale and
depend on physical properties (e.g., refractive index, density,
and the mixing state) and chemical composition of aerosol.
The aerosol chemical composition at Manora Peak is
dominated by mineral dust and carbonaceous aerosol; total
carbonaceous aerosol (TCA) contributing about 25% of TSP
with significantly lower contribution from absorbing EC
(∼1-2% of TSP) (18). The observed babs values at Manora
Peak are similar to those reported during ACE-Asia experiment (e.g., 15 Mm-1 (34)).
3.4. Site-Specific Mass Absorption Efficiency of EC
(MAE, σabs): Temporal Variability and Influence of Different
Emission Sources. The biomass burning is characterized by
relatively high σabs values compared to that from fossil-fuel
emissions (14). Recently, Schwarz et al. (15) have reported
a value of 13 ( 3 m2g-1 for σabs derived from biomass burning
sources. The MAE of EC (σabs) exhibits a large spatial and
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temporal variability, varying from 3.4 to 19.1 m2g-1 during
sampling period at different geographical locations in India
(Table 1). During wintertime (December 2004), average values
of σabs at different sampling sites are: 6.1 ( 2.0 m2g-1 at
Jaduguda (rural), 14.5 ( 1.1 m2g-1 at Manora Peak (highaltitude), 10.4 ( 1.4 m2g-1 at Mt. Abu (high-altitude) and
11.1 ( 2.6 m2g-1 at Allahabad (urban) and 11.3 ( 2.2 m2g-1
Hisar (urban). The long-term average σabs at Manora Peak
for February 05 to June 07 sampling period is 12.8 ( 2.9
m2g-1. A large variability in σabs values, ranging from 2 to 25
m2g-1, has been reported in literature depending on location,
composition, and the mixing state of BC in aerosols (16). For
example, Sharma et al. (10) have reported that median values
for site-specific attenuation cross-section ranges from 6.4 to
28.3 m2g-1 for different sites in Canada and have interpreted
this variability in terms of distribution of sources and
processes contributing to carbonaceous species at sampling
sites. An average of 10 m2g-1 is generally taken for σabs (10);
however, Bond and Bergstrom (9) had suggested a value of
7.5 ( 1.2 m2g-1 at 550 nm for uncoated soot particles. The
relatively high EC abundance (11.6 ( 2.0 µg m-3) and low
OC/EC ratio (3.1 ( 0.6) (Table 1) indicates dominance of
coal-based emissions at Jaduguda, resulting in low σabs value
(6.1 ( 2.0 m2g-1). The higher σabs values obtained at Manora
Peak, Hisar, and Allahabad could be attributed to the
predominance of aerosol species derived from biomass
burning emissions. A comparison of σabs values obtained in
present study and those reported in literature is presented
in Table 2.
3.5. Implications. The optical-attenuation (ATN), measured on thermo-optical EC-OC analyzer, has been used for
the simultaneous determination of EC abundance, absorption coefficient (babs), and mass absorption efficiency (σabs).
This is unlike the common approach of using two separate
instruments for the measurement of absorption coefficient
and thermal EC concentration to assess the σabs. This method
can serve as a reliable and relatively effective off-line
measurement of optical parameters. The results presented
in this study have relevance for the climate studies over south
Asian region where measurements of optical properties of
aerosols are lacking in literature. In addition, our study
documents large spatiotemporal variability in σabs values
(range: 3.4-19.1 m2g-1) for different geographical locations
representing urban, rural and high-altitude environments.
It is, thus, essential to use “site-specific” mass absorption
efficiency (σabs) rather than constant value conventionally
assigned for the optical instruments. Otherwise, it raises the
issue of uncertainty arising in the estimation of atmospheric
radiative forcing due to black carbon.
Acknowledgments
We thank Drs. N. Rastogi, R. Rengarajan, P. Hegde and Mr.
A.K. Sudheer for their help in collection of aerosol samples.
The partial funding support under Indian Space Research
Organization-Geosphere Biosphere Program (Bangalore,
India) is thankfully acknowledged. We thank three anonymous reviewers for their valuable comments and suggestions.
Supporting Information Available
Section A1: Assessment of errors in the measured parameters
on thermo-optical EC-OC analyzer; Section A2: Coulometer
based measurements of OC and EC; Section A3: Intercomparison of thermal EC concentration measured using ECOC analyzer and two-step thermal method; Tables S1-S4:
Measured parameters and associated uncertainties; Sampling
details and analytical data sets for high-altitude site (Manora
Peak) and an intercomparison of attenuation coefficient (bATN)
derived from EC-OC analyzer and Aethalometer. This material
is available free of charge via the Internet at http://
pubs.acs.org.
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Literature Cited
(1) Andreae, M. O.; Gelencser, A. Black carbon or brown carbon?
The nature of light-absorbing carbonaceous aerosols. Atmos.
Chem. Phys. 2006, 6 (10), 3131–3148.
(2) Jacobson, M. Z. Strong radiative heating due to the mixing state
of black carbon in atmospheric aerosols. Nature 2001, 409 (6821),
695–697.
(3) Menon, S.; Hansen, J.; Nazarenko, L.; Luo, Y. Climate effects of
black carbon aerosols in China and India. Science 2002, 297
(5590), 2250–2253.
(4) Pant, P.; Hegde, P.; Dumka, U. C.; Sagar, R.; Satheesh, S. K.;
Moorthy, K. K.; Saha, A.; Srivastava, M. K. Aerosol characteristics
at a high-altitude location in central Himalayas: Optical
properties and radiative forcing. J. Geophys. Res. 2006, doi:
10.1029/2005JD006768.
(5) Venkataraman, C.; Habib, G.; Eiguren-Fernandez, A.; Miguel,
A. H.; Friedlander, S. K. Residential biofuels in South Asia:
Carbonaceous aerosol emissions and climate impacts. Science
2005, 307 (5714), 1454–1456.
(6) Arnott, W. P.; Moosmuller, H.; Rogers, C. F.; Jin, T.; Bruch, R.
Photoacoustic spectrometer for measuring light absorption by
aerosol: Instrument description. Atmos. Environ. 1999, 33 (17),
2845–2852.
(7) Barnard, J. C.; et al. Measurements of Black Carbon Specific
Absorption in the Mexico City Metropolitan Area during the
MCMA 2003 Field Campaign. Atmos. Chem. Phys. 2005, 5, 4083–
4113.
(8) Weingartner, E.; Saathoff, H.; Schnaiter, M.; Streit, N.; Bitnar,
B.; Baltensperger, U. Absorption of light by soot particles:
Determination of the absorption coefficient by means of
aethalometers. J. Aerosol Sci. 2003, 34 (10), 1445–1463.
(9) Bond, T. C.; Bergstrom, R. W. Light absorption by carbonaceous
particles: An investigative review. Aerosol Sci. Technol. 2006, 40
(1), 1–41.
(10) Sharma, S.; Brook, J. R.; Cachier, H.; Chow, J.; Gaudenzi, A.; Lu,
G. Light absorption and thermal measurements of black carbon
in different regions of Canada. J. Geophys. Res. 2002, 107, D24,
DOI: 10.1029/2002JD002496.
(11) Yan, P.; Tang, J.; Huang, J.; Mao, J. T.; Zhou, X. J.; Liu, Q.; Wang,
Z. F.; Zhou, H. G. The measurement of aerosol optical properties
at a rural site in Northern China. Atmos. Chem. Phys. 2008, 8,
2229–2242.
(12) Yang, M.; Howell, S. G.; Zhuang, J.; Huebert, B. J. Attribution of
aerosol light absorption to black carbon, brown carbon, and
dust in ChinasInterpretations of atmospheric measurements
during EAST-AIRE. Atmos. Chem. Phys. 2009, 9, 2035–2050.
(13) Schmid, O.; Artaxo, P.; Arnott, W. P.; Chand, D.; Gatti, L. V.;
Frank, G. P.; Hoffer, A.; Schnaiter, M.; Andreae, M. O. Spectral
light absorption by ambient aerosols influenced by biomass
burning in the Amazon Basin. I: Comparison and field calibration
of absorption measurement techniques. Atmos. Chem. Phys.
2006, 6 (11), 3443–3462.
(14) Martins, J.; Artaxo, P.; Liousse, C.; Reid, J.; Hobbs, P.; Kaufman,
Y. Effects of black carbon content, particle size, and mixing on
light absorption by aerosols from biomass burning in Brazil. J.
Geophys. Res. 1998, 103, 32041–32050.
(15) Schwarz, J. Measurement of the mixing state, mass, and optical
size of individual black carbon particles in urban and biomass
burning emissions. Geophys. Res. Lett. 2008, DOI: 10.1029/
2008GL033968.
(16) Liousse, C.; Cachier, H.; Jennings, S. G. Optical and thermal
measurements of black carbon aerosol content in different
environments: Variation of the specific attenuation crosssection, sigma (σ). Atmos. Environ., Part A 1993, 27A (8), 1203–
1211.
(17) Rengarajan, R.; Sarin, M. M.; Sudheer, A. K. Carbonaceous and
inorganic species in atmospheric aerosols during wintertime
over urban and high-altitude sites in North India. J. Geophys.
Res. 2007, 112, D21307, DOI: 10.1029/2006JD008150.
(18) Ram, K.; Sarin, M. M.; Hegde, P. Atmospheric abundances of
primary and secondary carbonaceous species at two highaltitude sites in India: Sources and temporal variability. Atmos.
Environ. 2008, 42 (28), 6785–6796.
(19) Schauer, J. J.; et al. ACE-Asia intercomparison of a thermaloptical method for the determination of particle-phase organic
and elemental carbon. Environ. Sci. Technol. 2003, 37 (5), 993–
1001.
(20) Sciare, J.; Cachier, H.; Oikonomou, K.; Ausset, P.; Sarda-Estève,
R.; Mihalopoulos, N. Characterization of carbonaceous aerosols
during the MINOS campaign in Crete, July-August 2001: A
(21)
(22)
(23)
(24)
(25)
(26)
Downloaded by PHYSICAL RSCH LAB on October 29, 2009 | http://pubs.acs.org
Publication Date (Web): September 28, 2009 | doi: 10.1021/es9011542
(27)
(28)
(29)
(30)
(31)
(32)
(33)
(34)
(35)
multi-analytical approach. Atmos. Chem. Phys. 2003, 3, 1743–
1757.
Sandradewi, J.; Prévôt, A. S. H.; Weingartner, E.; Schmidhauser,
R.; Gysel, M.; Baltensperger, U. A study of wood burning and
traffic aerosols in an Alpine valley using a multi-wavelength
Aethalometer. Atmos. Environ. 2008, 42 (1), 103–112.
Chou, C. C.-K.; Chen, W.-N.; Chang, S.-Y.; Chen, T.-K.; Huang,
S.-H. Specific absorption cross-section and elemental carbon
content of urban aerosols. Geophys. Res. Lett. 2005, DOI: 10.1029/
2005GL024301.
Miyazaki, Y.; Kondo, Y.; Sahu, L. K.; Imaru, J.; Fukushima, N.;
Kanod, M. Performance of A Newly Designed Continuous Soot
Monitoring System (COSMOS). J. Environ. Monit. 2008, 10 (10),
1109–1240.
Junker, C.; Jennings, S. G.; Cachier, H. Aerosol light absorption in the
North Atlantic: trends and seasonal characteristics during the period
1989 to 2003. Atmos. Chem. Phys. 2006, 6, 1913–1925.
Watson,J. G.; Chow, J. C. Comparison and evaluation of in situ
and filter carbon measurements at the Fresno Supersite. J.
Geophys. Res. 2002, 107, DOI: 10.1029/2001JD000573.
ChouC. C.-K. ChenT.-K. HuangS.-H. LiuS. C. Radiative absorption capability of asian dust with black carbon contamination.
Geophys. Res. Lett. 2003, DOI: 10.1029/2003GL017076.
Snyder, D. C.; Schauer, J. J. An inter-comparison of two black
carbon aerosol instruments and a semi-continuous elemental
carbon instrument in the urban environment. Aerosol Sci.
Technol. 2007, 41 (5), 463–474.
Bodhaine, B. A. Aerosol absorption measurements at Barrow,
Mauna Loa and the south pole. J. Geophys. Res. 1995, 100 (D5),
8967–8975.
Clarke, A. D. Size distributions and mixtures of dust and black
carbon aerosol in Asian outflow: Physiochemistry and optical
properties. J. Geophys. Res. 2004, 109, D15S09, DOI: 10.1029/
2003JD004378.
Carrico, C. M.; Kus, P.; Rood, M. J.; Quinn, P. K.; Bates, T. S.
Mixtures of pollution, dust, sea salt, and volcanic aerosol during
ACE-Asia: Radiative properties as a function of relative humidity.
J. Geophys. Res. 2003, 108, D23, DOI: 10.1029/2003JD003405.
Hoffer, A.; Gelencser, A.; Guyon, P.; Kiss, G.; Schmid, O.; Frank,
G. P.; Artaxo, P.; Andreae, M. O. Optical properties of humiclike substances (HULIS) in biomass-burning aerosols. Atmos.
Chem. Phys. 2006, 611, 35633570.
Kirchstetter, T. W.; Novakov, T.; Hobbs, P. V. Evidence that the
spectral dependence of light absorption by aerosols is affected
by organic carbon J. Geophys. Res. 2004, 109, D21208, DOI:
10.1029/2004JD004999.
Dinar, E.; Riziq, A. A.; Spindler, C.; Erlick, C.; Kiss, G.; Rudich,
Y. Optical properties of absorbing aerosols containing model
and atmospheric HULIS. Faraday Discuss. 2008, 137, 279–295.
Bergstrom, R. W. Spectral absorption of solar radiation by
aerosols during ACE-Asia. J. Geophys. Res. 2004, 109, D19S15,
DOI: 10.1029/2003JD004467.
Reddy, M. S.; Venkataraman, C. Inventory of aerosol and sulphur
dioxide emissions from India: IsFossil fuel combustion. Atmos.
Environ. 2002, 36 (4), 677–697.
(36) Prasad, A. K.; Singh, R. P.; Kafatos, M. Influence of coal based
thermal power plants on aerosol optical properties in the IndoGangetic basin Geophys. Res. Lett. 2006, DOI: 10.1029/
2005GL023801.
(37) Edwards, J. D.; Ogren, J. A.; Weiss, R. E.; Charlson, R. J. Particulate
air pollutants: A comparison of British ‘Smoke’ with optical
absorption coefficients and elemental carbon concentration.
Atmos. Environ. 1983, 17 (11), 2337–2341.
(38) Adams, K. M.; Davis, L. I., Jr.; Japar, S. M.; Finley, D. R.; Cary,
R. A. Measurement of atmospheric elemental carbon: Realtime data for Los Angeles during summer 1987. Atmos. Environ.,
Part A 1990, 24 (3), 597–604.
(39) Petzold, A.; Niessner, R. Method comparison study on sootselective techniques. Mikrochim. Acta 1995, 117 (3-4), 215–
237.
(40) Kuhlbusch, T. A. J. Method for determining black carbon in
residues of vegetation fires. Environ. Sci. Technol. 1995, 29 (10),
2695–2702.
(41) Lavanchy, V. M. H.; Gaggeler, H. W.; Nyeki, S.; Baltensperger,
U. Elemental carbon (EC) and black carbon (BC) measurements
with a thermal method and an aethalometer at the high-alpine
research station Jungfraujoch. Atmos. Environ. 1999, 33 (17),
2759–2769.
(42) Hitzenberger, R.; Jennings, S. G.; Larson, S. M.; Dillner, A.;
Cachier, H.; Galambos, Z.; Rouc, A.; Spain, T. G. Intercomparison
of measurement methods for black carbon aerosols. Atmos.
Environ. 1999, 33 (17), 2823–2833.
(43) Moosmuller, H.; Arnott, W. P.; Rogers, C. F.; Bowen, J. L.; Gillies,
J. A.; Pierson, W. R.; Collins, J. F.; Durbin, T. D.; Norbeck, J. M.
Time-resolved characterization of diesel particulate emissions.
2. Instruments for elemental and organic carbon measurements.
Environ. Sci. Technol. 2001, 35 (10), 1935–1942.
(44) Mayol-Bracero, O. L.; Gabriel, R.; Andreae, M. O.; Kirchstetter,
T. W.; Novakov, T.; Ogren, J.; Sheridan, P.; Streets, D. G.
Carbonaceous aerosols over the Indian Ocean during the Indian
Ocean Experiment (INDOEX): Chemical characterization, optical properties, and probable sources. J. Geophys. Res. 2002, 107,
D19, DOI: 10.1029/2000JD000039.
(45) Huebert, B. J.; Bates, T.; Russell, P. B.; Shi, G.; Kim, Y. J.;
Kawamura, K.; Carmichael, G.; Nakajima, T. An overview of
ACE-Asia: Strategies for quantifying the relationships between
Asian aerosols and their climatic impacts. J. Geophys. Res. 2003,
108, D23, DOI: 10.1029/2004JD004700.
(46) Jeong, C. H.; Hopke, P. K.; Kim, E.; Lee, D. W. The comparison
between thermal-optical transmittance elemental carbon and
Aethalometer black carbon measuredat multiple monitoring
sites. Atmos. Environ. 2004, 38, 5193–5204.
(47) Quinn, P. K. Aerosol optical properties measured on board the
Ronald H. Brown during ACE-Asia as a function of aerosol
chemical composition and source region. J. Geophys. Res. 2004,
DOI: 10.1029/2003JD004010.
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