Airborne DOAS measurements in Arctic: vertical distributions of aerosol extinction coefficient and NO 2 concentration
International audience We report airborne differential optical absorption spectroscopy (DOAS) measurements of aerosol extinction and NO 2 tropospheric profiles performed off the North coast of Norway in April 2008. The DOAS instrument was installed on the Safire ATR-42 aircraft during the POLARCAT-F...
Published in: | Atmospheric Chemistry and Physics |
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Main Authors: | , , , , , , , , , , , , |
Other Authors: | , , , , , , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
HAL CCSD
2011
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Subjects: | |
Online Access: | https://hal.science/hal-00590730 https://hal.science/hal-00590730/document https://hal.science/hal-00590730/file/acp-11-9219-2011.pdf https://doi.org/10.5194/acp-11-9219-2011 |
Summary: | International audience We report airborne differential optical absorption spectroscopy (DOAS) measurements of aerosol extinction and NO 2 tropospheric profiles performed off the North coast of Norway in April 2008. The DOAS instrument was installed on the Safire ATR-42 aircraft during the POLARCAT-France spring campaign and recorded scattered light spectra in near-limb geometry using a scanning telescope. We use O 4 slant column measurements to derive the aerosol extinction at 360 nm. Regularization is based on the maximum a posteriori solution, for which we compare a linear and a logarithmic approach. The latter inherently constrains the solution to positive values and yields aerosol extinction profiles more consistent with independently measured size distributions. Two soundings are presented, performed on 8 April 2008 above 71° N, 22° E and on 9 April 2008 above 70° N, 17.8° E. The first profile shows aerosol extinction and NO 2 in the marine boundary layer with respective values of 0.04±0.005 km −1 and 1.9±0.3 × 109 molec cm −3 . A second extinction layer of 0.01±0.003 km −1 is found at 4 km altitude. During the second sounding, clouds prevented us to retrieve profile parts under 3 km altitude but a layer with enhanced extinction (0.025±0.005 km −1 ) and NO 2 (1.95±0.2 × 109 molec cm −3 ) is clearly detected at 4 km altitude. From CO and ozone in-situ measurements complemented by back-trajectories, we interpret the measurements in the free troposphere as, for the first sounding, a mix between stratospheric and polluted air from Northern Europe and for the second sounding, polluted air from Central Europe containing NO 2 . Considering the boundary layer measurements of the first flight, modeled source regions indicate closer sources, especially the Kola Peninsula smelters, which can explain the NO 2 enhancement not correlated with a CO increase at the same altitude. |
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