Geoscience Reference
In-Depth Information
are mostly associated with just a few key sources such as windblown soils,
sea spray, biomass burning, motor vehicles, and other combustion processes
associated with industry. The size distribution of trace metals is important,
since this not only influences the toxicity of a metal when inhaled but also
controls the extent to which metals may be dispersed via atmospheric trans-
port and hence is a prerequisite for the determination of rates of deposition
of metals to the Earth's surface. In India, such extensive investigations have
not yet been undertaken. Data on PM
10
and PM
2
.
5
from our experiments
will help link particle species observed at ambient receptor locations to
their sources, resulting in a means for developing effective emission control
strategies for primary particles and secondary particle precursor species.
Our main objective was to estimate some of the heavy metals such as
lead, mercury, cadmium, sodium, potassium, calcium, aluminium, and iron
in addition to ammonium, chloride, nitrate, and sulphate ions by Atomic
Absorption Spectrophotometry and Ion Chromatography and apportion
their most probable sources using the Chemical Mass Balance Model. Three
urban locations, namely, Behala Chowrasta, Rabindra Sadan, and Shyam
Bazaar Five Points were chosen within the city of Kolkata. One rural loca-
tion was chosen at the Indian Institute of Technology campus, Kharagpur,
a rural site in the Midnapur District of the state of West Bengal, India.
2. Methodology
1.
Sampling
: We sampled atmospheric aerosols from various Urban and
Rural locations in and around the city of Kolkata (as shown in Fig. 1),
which is one of the major metropolitan cities in the eastern India, using
a 5-stage Cascade Impactor (KIMOTO HVS-CPS 105) which automati-
cally fractionated the dust particles into five size fractions and we could
go up to the submicron range.
2.
Chemical analysis
: These size-fractionated dusts were then analyzed for
several key metals, anions, and cations, using suitable analytical tech-
niques. Atomic Absorption Spectrophotometry was used for estimation
involving metals and Ion Chromatography was used for the ions.
3.
Source apportionment
: US-EPA's Chemical Mass Balance Model (CMB-
Version 8.0) was used for apportioning the sources. The ambient data as
obtained in Step 2 serve as the input to the CMB, along with different
source profiles. For this, the various sources are identified and their con-
centration profiles were generated. The output gave quantitative mea-
surement of the relative contribution of each type of emission source.
