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| Titel |
Effect of aerosols and NO2 concentration on ultraviolet actinic flux near Mexico City during MILAGRO: measurements and model calculations |
| VerfasserIn |
G. G. Palancar, B. L. Lefer, S. R. Hall, W. J. Shaw, C. A. Corr, S. C. Herndon, J. R. Slusser, S. Madronich |
| 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 ; 13, no. 2 ; Nr. 13, no. 2 (2013-01-24), S.1011-1022 |
| Datensatznummer |
250017613
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| Publikation (Nr.) |
 copernicus.org/acp-13-1011-2013.pdf |
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| Zusammenfassung |
| Urban air pollution absorbs and scatters solar ultraviolet (UV) radiation,
and thus has a potentially large effect on tropospheric photochemical rates.
We present the first detailed comparison between actinic fluxes (AF) in the
wavelength range 330–420 nm measured in highly polluted conditions and
simulated with the Tropospheric Ultraviolet-Visible (TUV) model.
Measurements were made during the MILAGRO campaign near Mexico City in March
2006, at a ground-based station near Mexico City (the T1 supersite) and from
the NSF/NCAR C-130 aircraft. At the surface, measured AF values are
typically smaller than the model by up to 25% in the morning, 10% at
noon, and 40% in the afternoon, for pollution-free and cloud-free
conditions. When measurements of PBL height, NO2 concentration and
aerosols optical properties are included in the model, the agreement
improves to within ±10% in the morning and afternoon, and ±3%
at noon. Based on daily averages, aerosols account for 68% and
NO2 for 25% of AF reductions observed at the surface. Several
overpasses from the C-130 aircraft provided the opportunity to examine the
AF perturbations aloft, and also show better agreement with the model when
aerosol and NO2 effects are included above and below the flight
altitude. TUV model simulations show that the vertical structure of the
actinic flux is sensitive to the choice of the aerosol single scattering
albedo (SSA) at UV wavelengths. Typically, aerosols enhance AF above the PBL
and reduce AF near the surface. However, for highly scattering aerosols
(SSA > 0.95), enhancements can penetrate well into the PBL, while for
strongly absorbing aerosols (SSA < 0.6) reductions in AF are computed
in the free troposphere as well as in the PBL. Additional measurements of
the SSA at these wavelengths are needed to better constrain the effect of
aerosols on the vertical structure of the AF. |
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