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| Titel |
Spectral dependence of optical parameters of urban aerosols |
| VerfasserIn |
Charles Chou, Wei-Ru Huang, Chung-Yao Lin, Wei-Nai Chen |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250050195
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| Zusammenfassung |
| To improve understandings of the physico-chemical behavior of aerosols, an intensive aerosol
experiment was conducted at the Taipei Aerosol and Radiation Observatory (TARO) (22.5
oN, 121.5 oE). TARO is on the campus of the National Taiwan University in Taipei, Taiwan.
Because it locates around the center of the Taipei Basin, it is suitable for characterization of
aerosols in a subtropical mega-city. Besides, given that Taiwan is on the lee side of the
East-Asian winter monsoons, the properties of the Asian outflow aerosols can be measured
during specific episodes.
A three-wavelength integrating nephelometer (Model 3563, TSI Inc., MN) was employed
in measuring the light scattering coefficients of aerosols (Ïăs) at 450, 550, and 700 nm,
respectively. An aethalometer (Model AE-31, Magee Inc., CA) was used to measure the light
attenuation coefficients of aerosols (Ïăaeth) at 7 wavelengths (370, 470, 520, 590,
660, 880, and 950 nm). The Ïăaeth were in turn converted to the light absorption
coefficient of aerosols (Ïăa). In addition, for correcting the bias due to multi-scattering
effects in the aethalometer measurements, a photoacoustic spectrometer (Model
PASS-1, DMT Inc., CO) at 781 nm was applied to calibrate the aethalometer-based
Ïăa.
This study focused on the variations in the optical properties of aerosols measured at the
TARO during December 1-5, 2007, when Taipei switched from a typical urban
environment to being in the region of Asian continental outflow. It was found that the mass
concentration of aerosols and the values of optical parameters exhibited typical diurnal
patterns corresponding to the urban traffics while the local sources were dominating.
The diurnal amplitudes of BC and Ïăa were much larger than PM10 and Ïăs and,
consequently, the values of SSA dropped significantly during the daily rush hours. An air
parcel transported from the Asian mainland arrived Taipei in the early morning of
December 3, resulting in drastic increases of Ïăs and Ïăa; the hourly averaged Ïăs (550
nm) and Ïăa (520 nm) reached their respective maxima of 569 and 40 Mm-1. Note
that the increases in Ïăs were much stronger than in Ïăa. Consequently, the SSA
(520 nm) increased from 0.82 to 0.94. Moreover, it was revealed that the Angstrom
exponent of scattering (As) decreased slightly from 2.18 for local pollution period
to 2.00 for outflow episode, and the Angstrom exponent of absorption (Aa) kept
around 1.3 throughout the campaign. In contrast to As and Aa, the wavelength
dependency of SSA varied significantly; the episode averaged AÏ decreased from
0.10 for local pollution to 0.06 for AO period. It was found that the values of AÏ
exhibited significant anti-correlation with SSA, and that the values of SSA were
dominated primarily by BC content in aerosols. Nevertheless, as the aerosol composition
was stable, the scattering efficiency took the place of the dominant factor of SSA. |
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