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Atmospheric Environment 45 (2011) 3640e3644
Contents lists available at ScienceDirect
Atmospheric Environment
journal homepage: www.elsevier.com/locate/atmosenv
Short communication
Study of aerosol behavior on the basis of morphological
characteristics during festival events in India
Anubha Agrawal, Vinay K. Upadhyay 1, Kamna Sachdeva*
Department of Natural Resources TERI University, New Delhi 110070, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 October 2010
Received in revised form
28 March 2011
Accepted 4 April 2011
Two important festival events were selected to assess their impacts on atmospheric chemistry by
understanding settling velocity and emission time of aerosols. Using high volume sampler, aerosols were
collected in a sequential manner to understand settling velocity and emission time of aerosols on
a particular day. Composition and total suspended particulate load of the aerosols collected during the
festivals were used as markers for strengthening the assessment. Terminal settling velocity of the
aerosols were calculated using morphological and elemental compositional data, obtained from scanning
electron microcopy (SEM) and energy dispersive X-ray (EDX) study. Aerosol load, black carbon, aromatic
carbon and terminal velocity calculations were correlated to obtain conclusion that aerosols collected on
the festival day might have been emitted prior to the festival. Settling time of aerosols collected on 17th
and 19th October’09 during Diwali were found to be 36.5 (1.5 days) and 12.8 h, respectively. Carbon
concentration estimated using EDX was found to be almost double in the sample collected after 2 days of
the festival event. This strengthens our inference of time calculation where carbon with high concentration of load must have settled approximately after two days of the event. Settling time of aerosols
collected on Holi morning and afternoon was found to be 1.7 and 24.8 h, respectively. Further, because of
the small distance of 5.4 km between the meteorological station and sampling site, observed TSP values
were compared with theoretical load values, calculated by using visibility values taken from the meteorological data. And it was found that both experimental and calculated values are close to each other
about 50% of the times, which proves the assumption that experimental and meteorological data are
comparable.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Aerosol
Settling velocity
Indian festivals
Black carbon
Scanning electron microscopy
1. Introduction
In India some festivals are traditionally celebrated in a fabulous
manner, which usually releases huge quantities of air pollutants
(Kulshreshtha et al., 2004). Owing to various residence time of
different pollutants, adverse impacts on local atmospheric chemistry and human health often lasts for several days and months. One
of these impacts is the reduction in visibility (Jayaratne and Verma,
2001). On the basis of morphological characteristics and EDX analysis the composition, shape and size of the particulate pollutants
have been determined in the paper and is used to find their settling
velocities (Bowsher and Nichols, 1990; Kasahara et al., 1993;
Kasparian et al., 1998; Witt et al., 2010). Settling velocity calculations are done to determine the settling time of particulates and
* Corresponding author. Tel.: þ91 11 26122222; fax: þ91 11 26122874.
E-mail address: [email protected] (K. Sachdeva).
1
Present address: Central Pollution Control Board, Zonal office, Vadodara.
1352-2310/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.atmosenv.2011.04.006
peak load days. With these observations, festive events have been
explained as high concentration episodes (Ravindra et al., 2003;
Moreno et al., 2007; Steinhauser et al., 2008; Zhang et al., 2010).
In this study, two important Indian festivals, Diwali and Holi have
been studied. Huge amounts of fire crackers and sparklers are burnt
on the Diwali day, and in Holi, colored powder made of mixture of
inorganic material specifically metal salts, silica and chalk powder is
thrown by people at each other and it gets unwittingly dispersed in
air. The night preceding Holi festival, another event called as ‘Holika
dahan’ is performed all over the city, where huge quantity of
biomass is burnt, contributing to the increased aerosol load in the
atmosphere. Usually during these festivals, traffic density increases
immensely. This puts an additional pressure on the carrying
capacity of the local atmosphere. Moreover, Delhi is afflicted with
high concentration of aerosols load (Mönkkönen et al., 2004) due to
its semi-arid climatic conditions, re-suspension of crustal load, and
calm wind regimes during winter time.
Through this paper we report that morphology plays a crucial
role in settling of aerosols. Based on the shape obtained by the
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A. Agrawal et al. / Atmospheric Environment 45 (2011) 3640e3644
scanning electron microscope, shape correction factor the deposition velocity of particles has been calculated. Energy dispersive
X-ray analysis is used to ascertain the metals and carbon components present in the samples. Black Carbon (BC) and aromatic
organic carbon concentration (AOC) have also been estimated in
the samples. The main objectives of this paper is therefore to
compare aerosol load of two different festivals of India, and to
conduct systematic study using settling velocity concept to investigate the effects of these festivals on local atmospheric chemistry.
Table 1
Concentration of Black carbon (BC), Aromatic organic Carbon (AOC) and total suspended particulate matter (TSPM) in different samples collected during festival
events.
sampling date/time
% BC
%AOC
Conc.
in mg/m3
Diwali event
16th October 2009
17th October 2009
18th October 2009
19th October 2009
20th October 2009
21st October 2009
1.89
1.48
1.22
0.89
1.28
1.00
1.11
1.12
0.94
0.62
0.87
0.70
851.99
430.11
577.16
681.71
438.34
447.12
Hoili event
26th
27th
28th
28th
28th
28th
3.14
1.58
2.48
1.18
2.21
1.87
1.64
0.78
2.15
1.30
2.25
1.05
349.77
376.16
372.17
326.57
270.58
103.74
2.04
1.03
1.46
2.61
2.46
1.54
1.91
1.50
328.89
212.27
229.16
410.18
1.29
1.91
0.70
1.05
335.43
224.47
2. Sampling and methodology
The regional sampling was done in the south-west part of Delhi,
in TERI University (The Energy and Resources Institute), Vasant
Kunj using high volume sampler (Envirotech APM 460). This site is
situated (latitude 28 320 8900 N and longitude 77 080 5400 E) in an
institutional area and behaves as an ideal receptor site, because
predominant wind-direction of Delhi is south-west (Attri et al.,
2001). The collection of aerosols was started one day before the
event and continued for four days after Diwali. During Diwali
festival sampling was done on 24 hourly basis using glass fiber filter
paper.
For Holi, sampling was started three days before and continued
for next three days. Day before the Holi and on the Holi day
sampling was done on four hourly basis from 8 am till 8 pm, then
on 12 hourly basis from 8 pm to next day morning 8 am. This break
up of sampling was done to see the episodic effect of ‘Dhulandi’
(Holi with colors) usually played for 4 h with colors during day time
(8 ame12 pm) and ‘Holika Dahan’ event where high quantities of
biomass is burned.
SEM EDX- The surface morphology of aerosols was studied by
using scanning electron microscope (Sachdeva and Attri, 2008;
Witt et al., 2010). The samples collected on the glass fiber filter
were directly mounted on aluminum stubs and coated with a thin
layer of gold by sputter coater (SCD020) and seen under microscope
(model Leo 435 XP) at 15 kV (to restrict the beam penetration to
more than 0.99 mm) with band width of 16 mm equipped with
energy dispersive X-ray spectrometer (IMCAX-sight 759). It was
asume that sample collected on the filter paper was uniform and
small disc was cut to analyse samples on SEM machine. Disc portion
was selected randomly but 4 different areas in the same disc was
analysed for metal concentrations.
BC and AOC determination- Optical transmissionometer Model
OT21 (Magee scientific, USA) was used to determine BC and AOC
content of the aerosols deposited on the filter. The instrument
contains a dual wavelength light source of 880 nm and 370 nm for
the quantitative assessment of BC and AOC, respectively.
Deposition velocity calculation was done using Stoke’s law,
which determines the terminal velocity of an aerosol particle
undergoing gravitational settling in still air. A shape correction
factor (c) is also used to rectify the Stoke’s equation for our study
(Hind, 1999).
3. Results and discussion
1st
1st
1st
1st
Aerosol Samples were collected during two important festivals.
Samples were also collected before and after the event day to
compare the concentrations of aerosols emitted on the day of the
event. In the 24 hourly sampling of Diwali event it was found that
concentration one day prior to the event was 851.9 mg/m3 (Table 1).
This could correspond to the supplementary effect of high traffic
density during the festival times. Usually people move across the
city for exchanging gifts, and the ensuing traffic load is very high in
February2010
February 2010
February 2010
February 2010
February 2010
February/2010
March
March
March
March
2010
2010
2010
2010
8 ame12 pm
12 pme4 pm
4 pme8 pm
8 pme8 am
(next day)
8 ame12 pm
12 pme4 pm
4 pme8 pm
8 pme8am
(next day)
2nd March 2010
3rd March 2010
the week prior to the festival (Tandon et al., 2010). We have also
calculated the plausible aerosol concentration of that day using
meteorological value of visibility taken from the Palam airport
meteorological station. The distance between the weather station
and the study site is approximately 5.4 km, which is short enough
to justify its use for comparing with Diwali data collected at TERI
University. Hence, calculations of expected TSP concentration based
on weather station visibility data have been compared with
measured TSP.
The plausible aerosol concentration based on meteorological
data is approximately 462 mg/m3, which is lower from the observed
experimental values (Table 2). This difference could be attributed to
the difference in the sampling cycle. Visibility value is taken every
hour at the weather station. Observed experimental values are 24
hourly average values, which represent ambient air quality in
a more precise manner than the plausible values of the concentration. Due to high concentrations of aerosols during festival time,
visibility is seriously reduced. Sometimes the added load of aerosols can be as high as 390 mg/m3 (851e461) and visibility can be as
low as 1.4 km (Table 2).
We have also compared theoretically plausible and experimental values of visibility during Holi festival (Table 3). During
Holi week, it was observed that the meteorological visibility on
26th, 27th and 28th of February 2010 were 2.8, 3.1 and 2.9 km
respectively. And on the day of the festival, it was 3.8 km. The
Table 2
Aerosol load and visibility values (theoretical and calculated) in the sequential
sampling scheme during Diwali festival event.
Date
3.1. Aerosol load and visibility calculations
3641
Concentration Lv
Lv
Concentration
October.2009 Experimental
(mg/m3)
Theoretical
(taken from
Meteorological
department)
(km)
Calculated on
the basis if
aerosol load
(km)
Calculated
from theoretical
visibility values
(mg/m3)
16th
17th
18th
19th
20th
21st
2.6
2.8
2.4
2.4
2.9
3
1.4
2.7
2.0
1.7
2.7
2.6
461.5
428.5
500
500
413.7
400
851.9
430.1
577.1
681.7
438.3
447.1
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A. Agrawal et al. / Atmospheric Environment 45 (2011) 3640e3644
Table 3
Aerosols load and visibility values (theoretical and calculated) in the sequential sampling scheme during Holi festival event.
Date
26th February2010
27th February 2010
28th February 2010
1st March.2010
2nd March2010
3rd March.2010
Concentration
Lv
Lv
CONC
Experimental
(mg/m3)
Theoretical (taken from
Meteorological department) (km)
Calculated on the basis
if aerosol load (km)
Calculated from theoretical
visibility values (mg/m3)
349.76
376.15
268.26
295.12
330.41
191.64
2.8
3.1
2.9
3.8
3.9
2.9
3.4
3.1
4.4
4.0
3.6
6.2
428.57
387.09
413.79
315.78
307.69
413.79
Table 4
Elemental composition obtained from EDX analysis during two festival events.
Diwali
Holi
Elements
Date: 17th
October 2009
(day1) (%)
Date:19th
October 2009
(day2) (%)
Elements
Morning
(same day)
(%)
Afternoon
(same day)
(%)
Al
Si
S
Cl
K
Ca
Ba
C
Mg
Ti
Fe
15.55
8.67
9.30
3.15
23.20
6.35
6.12
25.07
2.25
0.33
0.00
7.66
22.84
2.69
1.60
5.00
11.91
0.00
43.23
0.00
0.00
5.07
C
Na
Mg
Al
Si
Cl
K
Ca
Fe
73.90
1.93
1.00
2.72
13.15
0.57
1.55
3.68
1.46
38.08
0
0
3.19
56.37
0
1.11
1.230
0
reason behind the increased visibility on the day of the event is the
decrease in the traffic density and industrial operations. The visibility calculated by empirical relation for the day of the event from
the average pollutant load of the day is equal to 4.06, which is
comparable to the meteorological value of the visibility. Thus,
Dhulandi being a small episodic event doesn’t distort the visibility
of the atmosphere to greater extent.
3.2. Analysis of black carbon and aromatic organics
in the Diwali and Holi samples
During Diwali event mass ratio of BC and AOC to aerosol load are
1.89e0.89% and 1.12e0.7%, respectively. This BC constituent can be
related to high traffic density, which is a common scenario during
Diwali time (Tandon et al., 2008). Mass ratios of BC and AOC are
highest on the day of Diwali and a day before Diwali event, proving
the festival to be a major carbon intensive event.
As per the EDX analysis (Table 4), carbon concentration in the
sample of Diwali day is only 25.07%. Hence, metals are the dominant constituents of the particulate load (Table 4) during Diwali,
therefore it could be inferred that metal pollution is of more
concern than the black carbon emissions from the event like Diwali,
as also found by Kulshreshtha et al. (2004) and Sarkar et al., 2010.
The higher concentrations of metals lead to lower mass ratios
of black carbon. The black carbon data has good correlation
(R2 ¼ 0.81) with aromatic organic carbon, and its emission is
usually associated with the organic carbon emissions, specifically
polycyclic aromatic hydrocarbons, as both of them are the main
components of soot (Cabada et al., 2004; Chu et al., 2004; Novakov
and Hansen, 2004). Further aromatic organic carbon percentage is
highly negatively correlated with total aerosol load. This indicates
that the TSP load is largely contributed by sources which do not
release aromatic carbon. This also strengthens the given conclusion
that metal and other crustal load contributes more to the aerosol
load as compared to black carbon and aromatic carbon during
Diwali festival day.
During Holi event aromatic carbon was found to have high
concentration particularly at the time of morning sampling
(Table 1). Holi is generally played during morning hours and colors
used for playing have high organic carbon contents in it like Malachite green (Velpandian et al., 2007). This contributes to organic
carbon content released during Holi. During Holi time black carbon
and aromatic carbon have very poor correlation, which indicates
that sources of organic carbon and black carbon during Holi time
are different whereas in Diwali samples they are the same.
3.3. Scanning electron microscopy and calculation
of setting velocity
Aerosols collected on the filter were subjected to scanning
electron microscope attached with X-ray diffraction facility.
Fig. 1. Scanning electron micrographs of Diwali samples: (a) image of aerosol sample collected on Diwali day (17th October, 2009). (b) Image of sample collected after two days of
event (19th October, 2009).
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A. Agrawal et al. / Atmospheric Environment 45 (2011) 3640e3644
3643
Fig. 2. Scanning electron micrographs of Holi samples: (a) morning (b) afternoon.
Scanning images of aerosols collected on both festival days were
viewed at 2000 (Figs. 1(a), (b) and 2(a), (b)) and images obtained
were used to calculate diameter of the aerosol aggregates. EDX
study has given quantitative data on composition of aerosol
aggregates in percentage (Table 4). The compositional data was
utilized to get average density of the aerosols which was additionally used to calculate terminal settling velocity. This terminal
velocity helped us to calculate estimated time of settling. According
to the SEM images, the aerosols emitted on Diwali day and two days
post Diwali was spherical in shape, with particle diameter 9.5 and
15 mm respectively. The settling velocities and settling time were
found to be 5.7 103 m/s and 36.5 h for Diwali day (17th October)
and 1.67 102 m/s and 12.8 h for 19th October. Similar type of
analysis was performed on aerosols collected during Holi festival,
using the images of SEM-EDX analysis. During Holi festival, EDX
analysis showed different result for two samples collected on the
same day in the interval of 4 h (Table 5). The different compositional results of EDX analysis show that there is great difference in
the average density of the aerosols collected at different times of
the day, which ultimately affected the settling velocity of the
aerosols. Aerosols emitted on the Holi day morning (8 ame12 pm)
and afternoon (12 pme4 pm) has average density of 2.22 g/cm3 and
1.915 g/cm3 respectively. In the two samples collected at different
intervals large difference is observed in the aerosol diameter. In the
morning sample, the diameter is 46 mm. And in the afternoon
sample, the diameter is 13 mm. And the settling velocity values vary
from 1.24 101 m/s in the morning to 8.5 103 m/s in the
afternoon. For the entire above calculations shape correction factor
(c) was also incorporated in the terminal settling velocity calculations (Table 5). Further for the calculation of the settling time, we
have assumed that particles were well mixed within the range of
1000 m planetary boundary layer (Thuillier and Lappe, 1964). Since
mean sea level height of Delhi is 239 m, distance of 761 m is taken
as the total height of mixing. With these calculations aerosols
Table 5
Result of aerosol particle density, terminal settling velocity and settling time
calculations done for festival events.
Diwali 1 (17thOctober)
Diwali 2 (19thOctober)
Holi1 (morning)
Holi2 (afternoon)
Average
density
in g/m3
Shape
correction
factor (c)
Terminal
settling
velocity
(Vts in m/s)
Settling
time
(hours)
2.12
2.44
2.22
1.91
Spherical
Spherical
1.09
1.09
5.7103
1.65102
1.24101
8.5103
36.5
12.8
1.7
24.8
collected on the Holi day (morning) must have taken 1.7 h to settle
down. And aerosols collected in the afternoon must have taken
24.8 h to settle down.
4. Conclusion
In this study we have tried to explain that festival events greatly
disturb the atmospheric chemistry at the event day. This inference
was drawn from SEM EDX analysis. Morphological characterization
is used to estimate aerosol diameter and shape correction factor
whereas EDX compositional data was used to calculate average
density. These three parameters were employed to find out
terminal settling velocity and the time of settlement. The analysis
has shown that difference in the morphology of the aerosols
changes the time of their settlement. Diwali samples were
observed to be composed of spherical aerosols, high concentrations
(56.95%) of metal, BC (1.89%) and AOC (1.11%). Hence, it is a big
pollutant event which releases metals in high quantities in atmosphere, is a carbon intensive episode and affects the atmospheric
chemistry for a maximum time period of 1.5 days after the occurrence of the episode. Metal concentration in Holi morning sample
was 12.91% and in Holi afternoon sample was 5.53%. which is not
very significant as compared to Diwali but during Holi morning
AOC concentration was found to be higher than Diwali (2.46%)
demonstrating the festival as a significant pollution episode.
Acknowledgement
The authors gratefully acknowledge support of Professor Attri’s
lab, SES JNU.
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