Aerosol Properties over Ranchi Measured from Aethalometer

doi:10.4236/acs.2011.13010

Paper Menu >>

Journal Menu >>

Atmospheric and Climate Sciences, 2011, 1, 91-94

doi:10.4236/acs.2011.13010 Published Online July 2011 (http://www.scirp.org/journal/acs)

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

E-mail: [email protected]

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.

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.

5. References

[1] A. Angstrom, “On the Atmospheric Transmission of Sun

Radiation and on Dust in the Air,” Geografiska Annaler,

Vol. 11, 1929, pp. 156-166. doi:10.2307/519399

[2] F. E. Volz, “Photometer mit Selen-Photoelement zur

spektralen Messung der Sonnenstrahlung und zur Bes-

timmung der Wellenlaengenabhaengigkeit de Dunsttrue-

bung,” Theoretical and Applied Climatology, Vol. 10, No.

1, 1959, pp. 100-131. doi:10.1007/BF02243122

[3] J. T. Twitty, “The Inversion of Aureole Measurements to

Derive Aerosol Size Distributions,” Journal of Atmos-

pheric Science, Vol. 32, No. 3, 1975, pp. 584-591.

doi:10.1175/1520-0469(1975)032<0584:TIOAMT>2.0.C

O;2

[4] Y. J. Kaufman, A. Gitelson, A. Karnieli, et al., “Size

Distribution and Scattering Phase Function of Aerosol

Particles Retrieve d From Sky Brightness Measurements,”

Journal of Geophysical Research, Vol. 99, No. D5, 1994,

pp. 10341-10345. doi:10.1029/94JD00229

[5] T. Nakajima, G. Tonna, R. Rao, et al., “Use of Sky

Brightness Measurements from Ground for Remote

Sensing of Particulate Polydispersions,” Applied Optics,

Vol. 35, No. 15, 1996, pp. 2672-2686.

doi:10.1364/AO.35.002672

[6] E. J. Highwood and R. P. Kinnersley, “When Smoke Gets

in Our Eyes: The Multiple Impacts of Atmospheric Black

Carbon on Climate, Air Quality and Health,” Environ-

ment International, Vol. 32, No. 4, 2006, pp. 560-566.

doi:10.1016/j.envint.2005.12.003

[7] M. S. Reddy and C. Venkataraman, “Atmospheric Opti-

cal and Radiative Effects of Anthropogenic Aerosol Con-

stituents from India,” Atmospheric Environment, Vol. 34,

No. 26, 2000, pp. 4511-4523.

doi:10.1016/S1352-2310(00)00105-9

[8] S. S. Babu and K. K. Moorthy, “Anthropogenic Impact

M. KUMAR ET AL.

on Aerosol Black Carbon Mass Concentration at a

Tropical Coastal Station: A Case Study,” Earth Sci ences,

Vol. 81, No. 9, 2001, pp. 1208-1214.

[9] K. M. Latha, K. V. S. Badrinath, “Seasonal Variation of

Black Carbon Aerosols and Total Aerosol Mass Concen-

trations over Urban Environment in India,” Atmospheric

Environment, Vol. 39, No. 22, 2005, pp. 4129-4141.

doi:10.1016/j.atmosenv.2005.04.004