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| Titel |
Nucleation and condensational growth to CCN sizes during a sustained pristine biogenic SOA event in a forested mountain valley |
| VerfasserIn |
J. R. Pierce, W. R. Leaitch, J. Liggio, D. M. Westervelt, C. D. Wainwright, J. P. D. Abbatt, L. Ahlm, W. Al-Basheer, D. J. Cziczo, K. L. Hayden, A. K. Y. Lee, S.-M. Li, L. M. Russell, S. J. Sjostedt, K. B. Strawbridge, M. Travis, A. Vlasenko, J. J. B. Wentzell, H. A. Wiebe, J. P. S. Wong, A. M. Macdonald |
| 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 ; 12, no. 7 ; Nr. 12, no. 7 (2012-04-02), S.3147-3163 |
| Datensatznummer |
250011003
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| Publikation (Nr.) |
 copernicus.org/acp-12-3147-2012.pdf |
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| Zusammenfassung |
| The Whistler Aerosol and Cloud Study (WACS 2010), included intensive
measurements of trace gases and particles at two sites on Whistler Mountain.
Between 6–11 July 2010 there was a sustained high-pressure system over the
region with cloud-free conditions and the highest temperatures of the study.
During this period, the organic aerosol concentrations rose from
<1 μg m−3 to ∼6 μg m−3. Precursor gas and aerosol
composition measurements show that these organics were almost entirely of
secondary biogenic nature. Throughout 6–11 July, the anthropogenic influence
was minimal with sulfate concentrations <0.2 μg m−3 and
SO2 mixing ratios ≈ 0.05–0.1 ppbv. Thus, this case provides
excellent conditions to probe the role of biogenic secondary organic aerosol
in aerosol microphysics. Although SO2 mixing ratios were relatively
low, box-model simulations show that nucleation and growth may be modeled
accurately if Jnuc = 3 × 10−7[H2SO4] and the organics
are treated as effectively non-volatile. Due to the low condensation sink
and the fast condensation rate of organics, the nucleated particles grew
rapidly (2–5 nm h−1) with a 10–25% probability of growing to CCN
sizes (100 nm) in the first two days as opposed to being scavenged by
coagulation with larger particles. The nucleated particles were observed to
grow to ∼200 nm after three days. Comparisons of size-distribution
with CCN data show that particle hygroscopicity (κ) was ∼0.1
for particles larger 150 nm, but for smaller particles near 100 nm the κ
value decreased near midway through the period from 0.17 to less than 0.06.
In this environment of little anthropogenic influence and low SO2, the
rapid growth rates of the regionally nucleated particles – due to
condensation of biogenic SOA – results in an unusually high efficiency of
conversion of the nucleated particles to CCN. Consequently, despite the low
SO2, nucleation/growth appear to be the dominant source of particle
number. |
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