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A real-time, online automated system for measurement of water soluble reactive Phosphate (SRP) ions in atmospheric particles Kalliopi Violaki, Ting Fang, Nikolaos Mihalopoulos, Rodney J. Weber, and Athanasios Nenes Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.6b01264 • Publication Date (Web): 15 Jun 2016 Downloaded from http://pubs.acs.org on June 16, 2016
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Analytical Chemistry
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A real-time, online automated system for measurement of water soluble
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reactive Phosphate (SRP) ions in atmospheric particles
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Kalliopi Violaki*1,2, Ting Fang2, Nikos Mihalopoulos1,5, Rodney. Weber2, Athanasios Nenes*2,3,4,5
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Department of Chemistry, University of Crete, Greece
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School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta;GA, 30332
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School of Chemical and Biomolecular Engineering, Georgia Institute of Technology,
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Atlanta;GA, 30332
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Patras, Greece
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Athens, Pendeli, Greece
Institute of Chemical Engineering Sciences, Foundation for Research and Technology, Hellas,
Institute for Environmental Research and Sustainable Development, National Observatory of
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ABSTRACT: We present a novel automated system for real-time measurements of
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water Soluble Reactive Phosphate (SRP) ions in atmospheric particles. Detection of SRP is
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based on molybdenum blue chemistry with Sn(II) chloride dihydrate reduction. The
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instrumentation consists of one particle-into-liquid sampler (PILS) coupled with a 250 cm
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path length Liquid Waveguide Capillary Cell (LWCC) and miniature fiber optic
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spectrometer, with detection wavelength set at 690 nm. The method detection limit was 0.4
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nM P, equivalent to 0.03 nmol P m-3 in atmospheric particles. Comparison of SRP in
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collocate PM2.5 aerosol filter sampling with the PILS-LWCC on line system were in good
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agreement (n=49, slope=0.84, R2 =0.78). This novel technique offers at least an order of
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magnitude enhancement in sensitivity over existing approaches allowing for SRP
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measurements of unprecedented frequency (8 min), which will lead to greater understanding
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of the sources and impacts of SRP in atmospheric chemistry.
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Keywords: Phosphate, SRP, dust, Liquid Waveguide Capillary Cell, PILS, atmosphere,
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biogeochemical P cycle. 1 ACS Paragon Plus Environment
Analytical Chemistry
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INTRODUCTION
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phosphorus (1,2). Of particular interest is the role of phosphorus in marine primary
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productivity, owing to its potential for affecting the concentration of atmospheric carbon
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dioxide (3) The atmosphere is considered as the principal source of externally-supplied
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nutrients for large areas of the surface ocean, and oligotrophic open oceans in particular (4).
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Therefore, atmospheric particles e.g. deposited desert dust could affect the trophic status of
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P-limited marine ecosystems. Atmospheric transport model simulations combined with the
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worldwide compilation of atmospheric Total Phosphorus (TP) and phosphate ions (PO43-)
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estimated the globally averaged TP at 1.39 Tg P y-1 and 0.24 Tg P y-1, respectively. Globally,
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terrigenous dust was found to be the dominant P source (82%), while biogenic particles
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(12%) and combustion inputs (5%) are comparable in non dusty regions (5).
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P in soil-derived dust is primarily in the form of apatite Ca5(PO4)3(F,Cl,OH), and to a lesser
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extent, P bound to iron minerals (6,7).Both of these forms exhibit limited solubility in sea
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water (8), yet P needs to solubilize to become bioavailable – in part because the insoluble
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fraction sinks quickly out of the euphotic zone. Estimates of soluble (bioavailable) P in
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atmospheric aerosol range widely, between 7 and 100% (5), with very little known on the
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mechanisms responsible for this variability. In a recent study (9) presented compelling
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evidence that acidification of desert dust particles from fossil fuel combustion (sulfur dioxide
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and sulfate aerosol) or other natural sources (volcanoes and DMS oxidation), can
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dramatically increase the fraction of bioavailable P in dust. Recent study show that
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atmospheric particles are highly acidic and insensitive to changes in anthropogenic sulfur
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emissions (10)Despite the observed decrease by 70%, over the past 15 years, of atmospheric
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sulfate concentrations in the southeastern United States and in many other regions globally,
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the estimated atmospheric particle pH was relatively stable (0–2) (10), suggesting that
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atmospheric acidification may be an important process.
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The most common analytical methods for offline determination of phosphate ion
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concentration in atmospheric aerosol samples are ion chromatography (IC) and
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spectrophotometry. The latter is based on the reaction of PO43- with molybdate complex in
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acidic solution forming a 12-molybdophosphoric acid and its subsequent reduction by
Primary productivity of continental and marine ecosystems is often limited or co-limited by
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Analytical Chemistry
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ascorbic acid or stannous chloride to the phosphomolybdenum blue complex, which its
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absorbance is measured by spectrophotometry (11). However, with this method the possible
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hydrolysis
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phosphomolybdate complexes due to the reaction in acidic conditions (pH
