Effect of aerosols and NO<sub>2</sub> concentration on ultraviolet actinic flux near Mexico City during MILAGRO: measurements and model calculations
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 s...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2013-01-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/13/1011/2013/acp-13-1011-2013.pdf |
| _version_ | 1811279772353822720 |
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| author | C. A. Corr S. C. Herndon J. R. Slusser W. J. Shaw S. R. Hall B. L. Lefer G. G. Palancar S. Madronich |
| author_facet | C. A. Corr S. C. Herndon J. R. Slusser W. J. Shaw S. R. Hall B. L. Lefer G. G. Palancar S. Madronich |
| author_sort | C. A. Corr |
| collection | DOAJ |
| description | 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, NO<sub>2</sub> 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 NO<sub>2</sub> 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 NO<sub>2</sub> 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. |
| first_indexed | 2024-04-13T01:01:50Z |
| format | Article |
| id | doaj.art-25abd0f0fd6c48889f8827d40017fb71 |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-04-13T01:01:50Z |
| publishDate | 2013-01-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-25abd0f0fd6c48889f8827d40017fb712022-12-22T03:09:27ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242013-01-011321011102210.5194/acp-13-1011-2013Effect of aerosols and NO<sub>2</sub> concentration on ultraviolet actinic flux near Mexico City during MILAGRO: measurements and model calculationsC. A. CorrS. C. HerndonJ. R. SlusserW. J. ShawS. R. HallB. L. LeferG. G. PalancarS. MadronichUrban 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, NO<sub>2</sub> 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 NO<sub>2</sub> 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 NO<sub>2</sub> 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.http://www.atmos-chem-phys.net/13/1011/2013/acp-13-1011-2013.pdf |
| spellingShingle | C. A. Corr S. C. Herndon J. R. Slusser W. J. Shaw S. R. Hall B. L. Lefer G. G. Palancar S. Madronich Effect of aerosols and NO<sub>2</sub> concentration on ultraviolet actinic flux near Mexico City during MILAGRO: measurements and model calculations Atmospheric Chemistry and Physics |
| title | Effect of aerosols and NO<sub>2</sub> concentration on ultraviolet actinic flux near Mexico City during MILAGRO: measurements and model calculations |
| title_full | Effect of aerosols and NO<sub>2</sub> concentration on ultraviolet actinic flux near Mexico City during MILAGRO: measurements and model calculations |
| title_fullStr | Effect of aerosols and NO<sub>2</sub> concentration on ultraviolet actinic flux near Mexico City during MILAGRO: measurements and model calculations |
| title_full_unstemmed | Effect of aerosols and NO<sub>2</sub> concentration on ultraviolet actinic flux near Mexico City during MILAGRO: measurements and model calculations |
| title_short | Effect of aerosols and NO<sub>2</sub> concentration on ultraviolet actinic flux near Mexico City during MILAGRO: measurements and model calculations |
| title_sort | effect of aerosols and no sub 2 sub concentration on ultraviolet actinic flux near mexico city during milagro measurements and model calculations |
| url | http://www.atmos-chem-phys.net/13/1011/2013/acp-13-1011-2013.pdf |
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