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      Chemical characterization and source apportionment of submicron aerosols measured in Senegal during the 2015 SHADOW campaign

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          Abstract

          <p><strong>Abstract.</strong> The present study offers the first chemical characterization of the submicron (PM<sub>1</sub>) fraction in western Africa at a high time resolution, thanks to collocated measurements of nonrefractory (NR) species with an Aerosol Chemical Speciation Monitor (ACSM), black carbon and iron concentrations derived from absorption coefficient measurements with a 7-wavelength Aethalometer, and total PM<sub>1</sub> determined by a TEOM-FDMS (tapered element oscillating microbalance&amp;ndash;filtered dynamic measurement system) for mass closure. The field campaign was carried out over 3 months (March to June 2015) as part of the SHADOW (SaHAran Dust Over West Africa) project at a coastal site located in the outskirts of the city of Mbour, Senegal. With an averaged mass concentration of 5.4<span class="thinspace"></span>µg<span class="thinspace"></span>m<sup>−3</sup>, levels of NR PM<sub>1</sub> in Mbour were 3 to 10 times lower than those generally measured in urban and suburban polluted environments. Nonetheless the first half of the observation period was marked by intense but short pollution events (NR PM<sub>1</sub> concentrations higher than 15<span class="thinspace"></span>µg<span class="thinspace"></span>m<sup>−3</sup>), sea breeze phenomena and Saharan desert dust outbreaks (PM<sub>10</sub> up to 900<span class="thinspace"></span>µg<span class="thinspace"></span>m<sup>−3</sup>). During the second half of the campaign, the sampling site was mainly under the influence of marine air masses. The air masses on days under continental and sea breeze influences were dominated by organics (36&amp;ndash;40<span class="thinspace"></span>%), whereas sulfate particles were predominant (40<span class="thinspace"></span>%) for days under oceanic influence. Overall, measurements showed that about three-quarters of the total PM<sub>1</sub> were explained by NR PM<sub>1</sub>, BC (black carbon) and Fe (a proxy for dust) concentrations, leaving approximately one-quarter for other refractory species. A mean value of 4.6<span class="thinspace"></span>% for the Fe<span class="thinspace"></span>∕<span class="thinspace"></span>PM<sub>1</sub> ratio was obtained. Source apportionment of the organic fraction, using positive matrix factorization (PMF), highlighted the impact of local combustion sources, such as traffic and residential activities, which contribute on average to 52<span class="thinspace"></span>% of the total organic fraction. A new organic aerosol (OA) source, representing on average 3<span class="thinspace"></span>% of the total OA fraction, showed similar variation to nonrefractory particulate chloride. Its rose plot and daily pattern pointed to local combustion processes, i.e., two open waste-burning areas located about 6 and 11<span class="thinspace"></span>km away from the receptor site and to a lesser extent a traditional fish-smoking location. The remaining fraction was identified as oxygenated organic aerosols (OOA), a factor that prevailed regardless of the day type (45<span class="thinspace"></span>%) and was representative of regional (approximately three-quarters) but also local (approximately one-quarter) sources due to enhanced photochemical processes.</p>

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          AERONET—A Federated Instrument Network and Data Archive for Aerosol Characterization

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            Ubiquity and dominance of oxygenated species in organic aerosols in anthropogenically-influenced Northern Hemisphere midlatitudes

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              Chemical and microphysical characterization of ambient aerosols with the aerodyne aerosol mass spectrometer.

              The application of mass spectrometric techniques to the real-time measurement and characterization of aerosols represents a significant advance in the field of atmospheric science. This review focuses on the aerosol mass spectrometer (AMS), an instrument designed and developed at Aerodyne Research, Inc. (ARI) that is the most widely used thermal vaporization AMS. The AMS uses aerodynamic lens inlet technology together with thermal vaporization and electron-impact mass spectrometry to measure the real-time non-refractory (NR) chemical speciation and mass loading as a function of particle size of fine aerosol particles with aerodynamic diameters between approximately 50 and 1,000 nm. The original AMS utilizes a quadrupole mass spectrometer (Q) with electron impact (EI) ionization and produces ensemble average data of particle properties. Later versions employ time-of-flight (ToF) mass spectrometers and can produce full mass spectral data for single particles. This manuscript presents a detailed discussion of the strengths and limitations of the AMS measurement approach and reviews how the measurements are used to characterize particle properties. Results from selected laboratory experiments and field measurement campaigns are also presented to highlight the different applications of this instrument. Recent instrumental developments, such as the incorporation of softer ionization techniques (vacuum ultraviolet (VUV) photo-ionization, Li+ ion, and electron attachment) and high-resolution ToF mass spectrometers, that yield more detailed information about the organic aerosol component are also described. (c) 2007 Wiley Periodicals, Inc.
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                Author and article information

                Journal
                Atmospheric Chemistry and Physics
                Atmos. Chem. Phys.
                Copernicus GmbH
                1680-7324
                2017
                September 01 2017
                : 17
                : 17
                : 10291-10314
                Article
                10.5194/acp-17-10291-2017
                8765f46c-04c9-4e4c-a05c-d47b85b02371
                © 2017

                https://creativecommons.org/licenses/by/3.0/

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