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| Titel |
Seasonal variation of secondary organic aerosol tracers in Central Tibetan Plateau |
| VerfasserIn |
R.-Q. Shen, X. Ding, Q.-F. He, Z.-Y. Cong, Q.-Q. Yu, X.-M. Wang |
| 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 ; 15, no. 15 ; Nr. 15, no. 15 (2015-08-10), S.8781-8793 |
| Datensatznummer |
250119955
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| Publikation (Nr.) |
 copernicus.org/acp-15-8781-2015.pdf |
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| Zusammenfassung |
| Secondary organic aerosol (SOA) affects the earth's radiation balance and
global climate. High-elevation areas are sensitive to global climate change.
However, at present, SOA origins and seasonal variations are understudied in
remote high-elevation areas. In this study, particulate samples were
collected from July 2012 to July 2013 at the remote Nam Co (NC) site,
Central Tibetan Plateau and analyzed for SOA tracers from biogenic
(isoprene, monoterpenes and β-caryophyllene) and anthropogenic
(aromatics) precursors. Among these compounds, isoprene SOA (SOAI)
tracers represented the majority (26.6 ± 44.2 ng m−3), followed
by monoterpene SOA (SOAM) tracers (0.97 ± 0.57 ng m−3),
aromatic SOA (SOAA) tracer (2,3-dihydroxy-4-oxopentanoic acid, DHOPA,
0.25 ± 0.18 ng m−3) and β-caryophyllene SOA tracer (β-caryophyllenic acid, 0.09 ± 0.10 ng m−3). SOAI tracers
exhibited high concentrations in the summer and low levels in the winter.
The similar temperature dependence of SOAI tracers and isoprene
emission suggested that the seasonal variation of SOAI tracers at the
NC site was mainly influenced by the isoprene emission. The ratio of
high-NOx to low-NOx products of SOAI (2-methylglyceric acid to
2-methyltetrols) was highest in the winter and lowest in the summer,
due to the influence of temperature and relative humidity. The seasonal
variation of SOAM tracers was impacted by monoterpenes emission and
gas-particle partitioning. During the summer to the fall, temperature effect
on partitioning was the dominant process influencing SOAM tracers'
variation; while the temperature effect on emission was the dominant process
influencing SOAM tracers' variation during the winter to the spring.
SOAM tracer levels did not elevate with increased temperature in the
summer, probably resulting from the counteraction of temperature effects on
emission and partitioning. The concentrations of DHOPA were 1–2 orders of
magnitude lower than those reported in the urban regions of the world. Due
to the transport of air pollutants from the adjacent Bangladesh and
northeastern India, DHOPA presented relatively higher levels in the summer.
In the winter when air masses mainly came from northwestern India, mass
fractions of DHOPA in total tracers increased, although its concentrations
declined. The SOA-tracer method was applied to estimate secondary organic
carbon (SOC) from these four precursors. The annual average of SOC was 0.22 ± 0.29 μgC m−3,
with the biogenic SOC (sum of isoprene,
monoterpenes and β-caryophyllene) accounting for 75 %. In the
summer, isoprene was the major precursor with its SOC contributions of
81 %. In the winter when the emission of biogenic precursors largely
dropped, the contributions of aromatic SOC increased. Our study implies that
anthropogenic pollutants emitted in the Indian subcontinent could be
transported to the TP and have an impact on SOC over the remote NC. |
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