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| Titel |
Evolution of aerosol chemistry in Xi'an, inland China, during the dust storm period of 2013 – Part 1: Sources, chemical forms and formation mechanisms of nitrate and sulfate |
| VerfasserIn |
G. H. Wang, C. L. Cheng, Y. Huang, J. Tao, Y. Q. Ren, F. Wu, J. J. Meng, J. J. Li, Y. T. Cheng, J. J. Cao, S. X. Liu, T. Zhang, R. Zhang, Y. B. Chen |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 14, no. 21 ; Nr. 14, no. 21 (2014-11-05), S.11571-11585 |
| Datensatznummer |
250119137
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| Publikation (Nr.) |
 copernicus.org/acp-14-11571-2014.pdf |
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| Zusammenfassung |
| A total suspended particulate (TSP) sample was
collected hourly in Xi'an, an inland megacity of China near the Loess Plateau,
during a dust storm event of 2013 (9 March 18:00−12 March 10:00 LT), along
with a size-resolved aerosol sampling and an online measurement of
PM2.5. The TSP and size-resolved samples were determined for elemental carbon (EC), organic carbon (OC),
water-soluble organic carbon (WSOC) and nitrogen (WSON), inorganic ions and
elements to investigate chemistry evolution of dust particles. Hourly
concentrations of Cl−, NO3−, SO42−, Na+ and
Ca2+ in the TSP samples reached up to 34, 12, 180, 72 and
28 μg m−3, respectively, when dust peak arrived over Xi'an. Chemical
compositions of the TSP samples showed that during the whole observation
period NH4+ and NO3− were linearly correlated with each other
(r2=0.76) with a molar ratio of 1 : 1, while SO42− and
Cl− were well correlated with Na+, Ca2+, Mg2+ and K+
(r2 > 0.85). Size distributions of NH4+ and
NO3− presented a same pattern, which dominated in the coarse mode
(> 2.1 μm) during the event and predominated in the fine
mode (< 2.1 μm) during the non-event. SO42− and
Cl− also dominated in the coarse mode during the event hours, but
both exhibited two equivalent peaks in both the fine and the coarse modes during the
non-event, due to the fine-mode accumulations of secondarily
produced SO42− and biomass-burning-emitted Cl- and the
coarse-mode enrichments of urban soil-derived SO42− and Cl−.
Linear fit regression analysis further indicated that SO42− and
Cl− in the dust samples possibly exist as Na2SO4, CaSO4
and NaCl, which directly originated from Gobi desert surface soil, while
NH4+ and NO3− in the dust samples exist as
NH4NO3. We propose a mechanism to explain these
observations in which aqueous phase of dust particle surface is formed via
uptake of water vapor by hygroscopic salts such as Na2SO4 and
NaCl, followed by heterogeneous formation of nitrate on the liquid phase and
subsequent absorption of ammonia. Our data indicate that 54 ± 20% and
60 ± 23% of NH4+ and NO3− during the dust
period were secondarily produced via this pathway, with the remaining derived
from the Gobi desert and Loess Plateau, while SO42− in the event
almost entirely originated from the desert regions. Such cases are different
from those in the East Asian continental outflow region, where during
Asia dust storm events SO42− is secondarily produced and
concentrates in sub-micrometer particles as (NH4)2SO4 and/or
NH4HSO4. To the best of our knowledge, the current work for the
first time revealed an infant state of the East Asian dust ageing process in the
regions near the source, which is helpful for researchers to understand the
panorama of East Asian dust ageing process from the desert area to the
downwind region. |
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