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Seasonal variability in light absorption particulate matter or soot in air at three stations in the South-Asian region situated in Nepal, India and Maldives
Stockholm University, Faculty of Science, Department of Meteorology .
Stockholm University, Faculty of Science, Department of Meteorology .
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Filter-based optical measurements of light absorbing particulate matter at awavelength of about 550 nm, referred to as soot, in air have been performed during theperiod from 1st June 2005 to 31th May 2009 at Godavari in Nepal, Sinhagad in India andHanimaadhoo in the Maldives. In order to reduce systematic errors due to the lightscattering of non-absorbing particles co-deposited on the filter, such as inorganic saltsand mineral dust, an additional sensor recording backscattered light was implemented.Two protocols of corrections (optical and chemical) were applied to the samplescollected at the observatories. The Indian monsoon circulation with its two annualphases in combination with the location of the combustion sources and their contributionrelative other non-anthropogenic sources dominated the observed patterns of soot at theobservatories in India and Maldives. The observatory in Nepal was however mainlyinfluenced by combustion sources all year around concealing possible variability relatedto the monsoon circulation. At the receptor observatory in the Maldives, peak values inthe soot absorption coefficient occurred during the winter season (December to April)when air was transported from the polluted Indian subcontinent out over the IndianOcean. A close to two orders of magnitude lower values were recorded in air that hadspent more than 10-days over the Indian Ocean during the monsoon season (July toSeptember), suggested to be dominated by particulate matter from remote marinebiogenic sources.

National Category
Meteorology and Atmospheric Sciences
Identifiers
URN: urn:nbn:se:su:diva-30837OAI: oai:DiVA.org:su-30837DiVA: diva2:274352
Available from: 2009-10-28 Created: 2009-10-28 Last updated: 2013-07-09Bibliographically approved
In thesis
1. Characterization of soot in air and rain over southern Asia
Open this publication in new window or tab >>Characterization of soot in air and rain over southern Asia
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Filter-based optical measurements of light absorbing particulate matter at awavelength of about 550 nm, here referred to as soot, in air and rainwaterhave been performed during the period from 1st June 2005 to 31th May 2009at Godavari in Nepal, Sinhagad in India and Hanimaadhoo in The Maldives.A method for determination of water-insoluble light absorbing matter inrainwater has been developed. Analysis of environmental samples has beensuccessfully performed with the described method on samples collected atHanimaadhoo and Godavari. At Hanimaadhoo the average soot concentrationin rainwater was 48 mgl-1 and at Godavari 86 mgl-1.In order to reduce systematic errors at optical determination of soot due tothe light scattering of non-absorbing particles co-deposited on the filter, suchas inorganic salts and mineral dust, an additional sensor recording backscatteredlight was used. Two alternative protocols of corrections (optical andchemical) were applied to the samples. Simultaneous measurements of sootand inorganic ions in aerosol and precipitation at Hanimaadhoo during theperiod May 2005 to February 2007 made it possible to calculate the washoutratio (WR) of these components as a measure of how efficiently they are scavengedby precipitation. During the monsoon season the WR for soot was similarto that of sulphate and other fine mode aerosol components, indicating thatsoot containing particles in these situations were efficient as cloud condensationnuclei. During the polluted winter days, on the other hand, the WR forsoot was 3 times smaller than that of sulphate, showing that the soot containingparticles had retained a hydrophobic character even after a travel time ofseveral days.The Indian monsoon circulation with its two annual phases in combinationwith the location of the main combustion source areas dominated the observedpatterns of soot at the observatories in India and Maldives. Godavari in Nepalwas however mainly influenced by combustion sources all year around concealingpossible variability related to the monsoon circulation. At Hanimaadhoo,peak values in the soot concentration occurred during the winter season(December to April) when air was transported from the polluted Indian subcontinentout over the Indian Ocean. At least a factor of ten lower values wererecorded in air that had spent more than 10-days over the Indian Ocean duringthe monsoon season (July to September).

 

Place, publisher, year, edition, pages
Stockholm: Department of Meteorology , Stockholm University, 2009. 42 p.
Keyword
soot, black carbon, atmospheric concentration, light absorption, wet deposition, scavenging, wash-out ratio, South-Asia.
National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:su:diva-30861 (URN)978-91-7155-969-2 (ISBN)
Public defence
2009-11-27, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defence, the following papers were unpublished and had a status as follows: Paper 1: Submitted. Paper 2: Manuscript. Paper 3: Submitted: Paper 4: Submitted.Available from: 2009-11-05 Created: 2009-10-28 Last updated: 2009-10-29Bibliographically approved

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