Mineral and anthropogenic aerosols over Arabian Sea and Bay of Bengal

1
Mineral and anthropogenic aerosols over
Arabian Sea and Bay of Bengal Ashwini Kumar
and M.M.Sarin E-mail ashwini_at_prl.res.in Physica
l Research Laboratory Ahmedabad-380 009 India
SOLAS Open Science Conference, Barcelona, 16
19 Nov, 2009
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Winter Monsoon
Continental Outflow
Bay of Bengal
Arabian Sea
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Wind Streamlines over Arabian sea and Bay of
Bengal
July - September
October - March
April - June
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Integrated Optical depth at 630 nm Rajeev et al,
2000 Collins et al, 2001 Ramnathan et al, 2001
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ORV Sagar Kanya Cruise Tracks
18-27 Feb 2001
2-22 Mar 2001
15 Sept- 12 Oct 2002
19-27 Feb 2003
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18 Mar 12 May, 2006
27 Dec 08 28 Jan 09
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Sea-Salt Characteristics
Bay of Bengal
Sea-water Line
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Dominance of Anthropogenic Sources
Bay of Bengal
11
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Characteristics of Dust Bay of Bengal
Crustal Line
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Average water-soluble composition of aerosols
over Bay of Bengal and Arabian Sea, reflecting
dominance of SO42-.
Arabian Sea, 2001, 06, 07
Bay of Bengal, 2001-2009
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Bay of Bengal, Sep-2002
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Enhanced solubility of Calcium as dust (CaCO3)
undergoes neutralization process with acidic
species
Kumar, Sarin and Sudheer, Atm. Env., 2008
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SO42- - rich aerosols Implications to Cl- loss
Bay of Bengal
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Arabian Sea
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Models on Global scale
Surface SO2 Conc. Overestimated (factor of 2)
SO42- Underestimated (Substantial
uncertainty
associated with
aerosol chemistry)
Uptake oxidation of sulphur compounds inside
the aqueous phase of sea-salt particles-Not
considered
Uptake
SO42-
Sea-salt particle
2NaCl H2SO4 Na2SO4 2HCl
Increase
Decrease
Mean particle size
SO42- conc.
Decrease CCN
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Implications
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Carbonaceous Aerosols
First measurements of carbonaceous species over
this region.
Sudheer and Sarin, Atm. Env.,2008
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North-BoB

• by invoking additional sources for OC other than
  the primary combustion source
• (2) formation of significant secondary organic
  aerosols during the transport
• (3) due to the differences in the atmospheric
  life-time of EC and OC favouring preferential
  removal of one component over the other during
  transport

Central and south-BoB
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OC/EC ratio shows a decreasing trend suggesting
that the rate of decrease in OC concentrations is
higher than that of EC.
This difference in residence time can be
attributed to the differences in their particle
size, volatility, reactivity and scavenging
efficiency.
EC is thermally stable and nonvolatile while OC
contains several semi-volatile species that can
partition between the particle and gas phases.
Also the scavenging rate of OC is expected to
be high, because a substantial amount of OC is
generally water-soluble and, thus, undergoes
hygroscopic growth and preferential removal.
Sudheer and Sarin, Atm. Env.,2008
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Paytan et al, PNAS, 2009
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Bay of Bengal
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Mahowald et. al, 2009, Ann. Rev. Mar. Sci.
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Solubility of aerosol iron and role of
anthropogenic sources (Mt.Abu)
Mt Abu, 1700 m asl, clean site
Bay of Bengal
Arabian Sea
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Solubility of aerosol iron and role of
anthropogenic sources (Mt.Abu)
Kumar and Sarin, Tellus-B (2009)
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Aerosol iron solubility over Bay of Bengal
(ICARB-2009)
Combustion sources
chemical processing
Kumar, Sarin, and Srinivas (Unpublished)
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• Summary
• Mineral dust and anthropogenic species dominate
  the chemical composition of aerosols over Bay of
  Bengal and Arabian Sea
• Chemical uptake of nss-SO42- by mineral dust
  (CaCO3 ) is an important process in the MABL of
  both the oceanic regions.
• Large depletion of chloride (range12-100)
  suggests sea-salt as a potential sink for SO2 in
  the MABL.
• Fe/Al ratio enrichment of Fe suggests its
  potential source from combustion processes
  vis-à-vis chemical processing of mineral dust
  associated with continental outflow.

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Thanks

• Acknowledgement
• Dr. Neeraj Rastogi
• Dr. R. Rengarajan
• Mr. A.K.Sudheer
• Mr. B. Srinivas