Atmospheric and Climate Sciences, 2011, 1, 91-94
doi:10.4236/acs.2011.13010 Published Online July 2011 (http://www.scirp.org/journal/acs)
91
Aerosol Properties over Ranchi Measured from
Aethalometer
Manoj Kumar, Kumari Lipi, S. Sureshbabu1, N. C. Mahanti
Centre of Excellence in Climatology, Department of Ap pl i e d Mat hematics , Ranchi, India
1Space Physics Laboratory, Vikram Sarabhai Space Centre, Thiruvananthapuram, In d ia
Received April 21, 2011; revised May 27, 2011; accepted June 9, 2011
Abstract
Continuous and near-real-time measurements of the mass concentration of Aerosol Black Carbon (BC) were
carried out 1st to 31st July 2010 of rainy season and compare with data of July-2010 to March-2011 using an
Aethalometer (model AE-31 of Magee Scientific, USA). The principle of the Aethalometer is to measure the
attenuation of a beam of light transmitted through a filter, while the filter is continuously collecting an aero-
sol sample. This measurement is made at successive regular intervals of a time base period has been the BC
mass concentration is estimated by measuring the change in the transmittance of a quartz filter tape, on to
which the particles impinge. The instrument was operated at a time base of 5 min, round the clock with a
flow rate of 4-liter min–¹, to study the impact of rainy season on black carbon concentrations over a typical
urban environment namely Ranchi, India. BC concentrations were high during morning (0600 to 0900 h) and
evening hours (1900 to 2300 h) compared to afternoon hours. During early morning hours, high values of BC
are attributed to the turbulence set-in by the solar heating which breaks the night-time stable layer and aero-
sols in the nocturnal residual layer are mixed up with those near the surface.
Keywords: Black Carbon (BC), Aethalometer, Aerosol
1. Introduction
For several decades optical properties of aerosols have
been an important subject in atmospheric research. Ang-
strom (1929) [1] found an emp irical relatio nship betw een
the size of the aerosol particles and the wavelength de-
pendence of the extinction coefficient. Since Volz (1959)
[2] introdu c ed the first handheld analogue instrument, the
technology of ground based atmospheric aerosol meas-
urements using sun photometry has change d substantially.
The observations, so far have been limited to poin t meas-
urements through balloon s, flux towers etc.
Modern Aethalometer can automatically collect data
continuously with greater accuracies. The measured sky
spectral radiances can be used to obtain the different op-
tical and size properties of the aerosols in the total at-
mospheric column (Twitty, 1975 [3]; Kaufman et al.,
1994 [4]; Nakajima et al., 1996 [5] ). The principle is ba-
sed on the dependence of the light scattering phase func-
tion on aerosol particle size and wavelength. The radia-
tive effects of BC cannot be neglected as it is dominant
light-absorbing component of atmospheric aerosols. Ac-
curate information on BC is essential for the predictions
of the radiative forcing caused by Black Carbon Aerosols.
Relatively small changes in the BC input data can change
the radiative forcing from positive to n egative (Haywood
and Shine, 1995 [6]) .Several studies have shown that
BC has typical lifetimes ranging from 1 week to 10 days
in the absence of precipitation (Reddy and Venkataraman,
2000 [7]; Babu and Moorthy, 2001[8])
2. Data Used
Continuous and near-real-time measurements of the mass
concentration of aerosol BC were carried out July 2010
using an Aethalometer; model AE-31 of Magee Scien-
tific, USA .provided by Space Physics Laboratory, Vik-
ram Sarabhai Space Centre Thiruvananathapuram. The
AE-31 series performs optical analysis at seven different
wavelengths from 370 nm to 950 nm and has found
widespread application in studies of atmospheric optics,
radiative transfer etc. The BC mass concentration esti-
mated by measuring the change in the transmittance of a
quartz filter tape on to which the particles impinge. The

92 M. KUMAR ET AL.
instrument was operated at a time base of 5 min, round
the clock with a flow rate of 4-liter min–¹, the instrument
has been factory calibrated and errors in the measure-
ments are ~ ± 2.
The AE-31 series ‘Spectrum’ models of Aethalometer
use an optical source assembly that incorporates seven
different solid-state light sources. These sources are ac-
tivated sequentially to illuminate the aerosol sample at
seven discrete wavelengths each time base cycle. In this
way, we determined the optical attenuation at seven
points across the spectrum from ultraviolet to near infra-
red. The AE-31 series adds analysis in the near-ultra-
violet at 370 nm, which responds with great sensitivity to
aromatic organic species that are found in tobacco smoke,
wood fire smoke, and fresh diesel exhaust.
3. Case Study
In the present study, measurements of Black Carbon Ae-
rosols was carried out during July to study the impact of
rainy season on black carbon concentrations over a typi-
cal urban environment namely Ranchi, India. Diurnal
variations BC suggest that the concentrations on rainy
days reaches lowest value up to (~ 1591 ng/m3) and high-
est value up to (~ 5850 ng/m3) during morning (06:00 to
9:0 0 h ) and evening hours (19:00 to 23:00 h) lowest v alu e
reaches up to (~ 717 ng/m3) and highest value reaches
upto (~ 2730 ng/m3) were high compared to afternoon
hours. During early morning hours, high values of BC
are attributed to the turbu lence set-in by th e solar heating
which breaks the night-time stable layer and aerosols in
the nocturnal residual layer are mixed up with those near
the surface. Low values of BC during afternoon hours
are attributed to the dispersion of aerosols, due to in-
crease in boundary layer height. Sensitivity studies of the
accuracy of the inversion have shown ~ ± 2 per cent er-
rors in most situations for data. In order to screen out the
effects of clouds, storm and clear sky weather, all the
data shown were passed a ~ ± 2 error self-consistency
Figure 1. Diurnal variation of BC on very clear days from
July 10 to March 11.
testing criteria. Preliminary results of the data are pre-
sented.
Figure 1 shows the diurnal variation of black carbon
aerosols at Ranchi during July-10 to March-11 on se-
lected few days. The concentration of BC is measured in
nano gram per cubic meter (ng/m3) using the Aethalom-
eter. It reveals that BC concentration is high during mor-
ning and evening periods for all the days. The BC con-
centration shows the enhancement during 06:30 hr to
9:30 hr and a decreasing trend s afterwards till noon. The
BC concentration remains almost constant till late noon
and start increasing again at around 18:00 hr till midnight.
During nighttime BC concentration is high in compari-
son to daytime. During early morning, high values of BC
have been attributed due to fumigation effect within the
boundary layer, which brings in aerosols from the noc-
turnal residual layer. Shortly after sunrise, the concentra-
tion stars decreasing. The peak around 8:30 AM is due to
morning traffic. Low values of BC during afternoon
hours have been attributed to the dispersion of aerosols
due to the turbulence caused by the solar heating which
breaks the night time stable layer, and also due to in-
crease in boundary layer height in addition to the low
traffic density.
In Figure 2 Comparison of BC during clear and rainy
days has been done. The peak value of BC during clear
days reaches up to (~ 29154 ng/m3) at 00:45 hrs, while
during rainy days it reache s only up to (~ 5850 ng/m3) at
06:10 hrs. This may be attributed due to washout of BC
due to rain. BC significantly reduces after rainfall due to
scavenging process and also due to reduction in the
Figure 2. Diurnal variation of BC during rainy days.
Figure 3. Diurnal variation of BC during weekend & clear
days.

M. KUMAR ET AL.
93
Figure 4. Diurnal variation of Aerosol concentration on
rainy season of July on 880 nm black carbon concentration
on hourly basis for July 10.
continental featu res conductive for aerosol generation by
shifting the air mass (Latha and Badarinath [9], 2005).
During daytime from 12:30 to 17:30 hrs, high BC values
are observed during rainy days in comparison to clear
days; which may be due to cloud cover during rainy days
in comparison to clear days; which may be due to cloud
cover during rainy days because the boundary layer is
reduced during rainy days. Similarly, a comparison of
BC concentration during clear day and weekend has been
done (Figure 3), which shows that on clear day has
higher BC concentration is observed in comparison to
weekend, because at weekend vehicular pollution and
other daily buses of school and official vehicle has
closed. The peak value of BC during clear day reaches
upto (~ 4658ng/m3) at 0600 to 0900 hours while during
weekend it reaches only up to (~ 2683ng/m3) at 0600 to
0900 hrs.
In Figure 2, Comparison of BC during clear and rainy
days has been done. The peak value of BC during clear
days reaches up to (~ 29154 ng/m3) at 00:45 hrs, while
during rainy days it reaches only up to (~ 5850ng/m3) at
06:10 hrs. This may be attributed due to washout of BC
due to rain. BC significantly reduces after rainfall due to
scavenging process and also due to reduction in the con-
tinental features conductive for aerosol generation by
shifting the air mass (Latha and Badarinath [9], 2005).
During daytime from 12:30 to 17:30 hrs, high BC values
are observed during rainy days in comparison to clear
days; which may be due to cloud cover during rainy days
in comparison to clear days; which may be due to cloud
cover during rainy days because the boundary layer is
reduced during rainy days. Similarly, a comparison of
BC concentration during clear day and weekend has been
done (Figure 3), which shows that on clear day has
higher BC concentration is observed in comparison to
weekend, because at weekend vehicular pollution and
other daily buses of school and official vehicle has
closed. The peak value of BC during clear day reaches
up to (~ 4658ng/m3) at 06:00 to 09:00 hours while during
weekend it reache s only up to (~ 2683ng/m3) at 06:00 to
09:00 hrs.
In Figure 4, the black car bon (BC) concentration dur-
ing the month of July during rainy season (July-10),
shows similar pattern of increasing trend at morning and
evening and decreasing at afternoon time in comparison
to rest of the selected days of different month shown in
Figure 1.
4. Conclusions
Summarizing, the first study of aerosol optical properties
and conc. distributions for the atmospheric column over
Ranchi using Aethalometer have given great promise for
future detailed studies of the origins of high pollution
episodes in the region.
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