Abstract
Abstract. Coincident aerosol observations of multi-axis differential optical absorption spectroscopy (MAX-DOAS), cavity ring-down spectroscopy (CRDS), lidar, and sky radiometer were conducted in Tsukuba, Japan, on 5–18 October 2010. MAX-DOAS aerosol retrieval (for aerosol extinction coefficient and aerosol optical depth at 476 nm) was evaluated from the viewpoint of the need for a correction factor for oxygen collision complexes (O4 or O2–O2) absorption. The present study strongly supports this need, as systematic residuals at relatively high elevation angles (20 and 30°) were evident in MAX-DOAS profile retrievals conducted without the correction. However, adopting a single number for the correction factor (fO4 = 1.25) for all of the elevation angles led to systematic overestimation of near-surface aerosol extinction coefficients, as reported in the literature. To achieve agreement with all three observations, we limited the set of elevation angles to ≤10° and adopted an elevation-angle-dependent correction factor for practical profile retrievals with scattered light observations by a ground-based MAX-DOAS. With these modifications, we expect to minimize the possible effects of temperature-dependent O4 absorption cross section and uncertainty in DOAS fit on an aerosol profile retrieval, although more efforts are encouraged to quantitatively identify a physical explanation for the need of a correction factor.
Highlights
Atmospheric aerosols play a critical role in controlling the Earth’s climate and air quality (IPCC, 2013)
Coincident aerosol observations by MAX-DOAS and those by cavity ring-down spectroscopy (CRDS), lidar, and sky radiometer were conducted in Tsukuba, Japan, on 5–18 October 2010
This differs from the situation during the Campaign of Nitrogen Dioxide measuring Instruments (CINDI) campaign period, when the uplifted aerosols could be attributed to the discrepancy found in comparisons between MAX-DOAS and the ground-based humidified nephelometer (Zieger et al, 2011; Irie et al, 2011)
Summary
Atmospheric aerosols play a critical role in controlling the Earth’s climate and air quality (IPCC, 2013). During the CINDI campaign, besides the intercomparison for NO2, near-surface aerosol extinction coefficients (AECs) retrieved from observations from four different MAX-DOAS instruments were compared to those measured by the in situ humidified nephelometer (Zieger et al, 2011). Coincident aerosol observations by MAX-DOAS and those by cavity ring-down spectroscopy (CRDS), lidar, and sky radiometer were conducted in Tsukuba, Japan, on 5–18 October 2010. This occasion was used to evaluate the MAX-DOAS aerosol retrievals of AECs and aerosol optical depth (AOD) at 476 nm, from the viewpoint of the need for a correction factor for O4 absorption. Potential practical solutions to achieve agreement of the MAX-DOAS observations with the three other observations are discussed
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