Dual-wavelength aerosol vertical profile measurements by MAX-DOAS at Tsukuba, Japan

H Irie,H Akimoto,K Aoki,Y Kanaya,A Shimizu,H Iwabuchi

doi:10.5194/acp-9-2741-2009

Abstract

Abstract. We present vertical profiles of the aerosol extinction coefficient retrieved from ground-based Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements at Tsukuba, Japan (36.1° N, 140.1° E), from November 2006 to March 2007. Retrievals utilizing absorption by the oxygen collision complex O4 are first made at two wavelengths, 354 and 476 nm. A robust assessment of the MAX-DOAS aerosol data is then made using coincident lidar measurements throughout the period. Agreement between aerosol extinction coefficients measured by MAX-DOAS and the lidar tends to be better at the longer wavelength and at lower altitudes. At 476 nm, the best agreement, to within 30%, is found at altitudes of 0–1 km, confirming results from a literature assessment for a two-month measurement period. These findings are supported by comparisons between aerosol optical depths derived from MAX-DOAS and sky radiometer measurements and are further explained by differences in the altitude-dependent measurement sensitivity to the aerosol extinction coefficient between 354 and 476 nm. Thus, uncertainty in MAX-DOAS aerosol measurements is well quantified and characterized, providing a basis for quantitative studies using MAX-DOAS measurements.

Highlights

Atmospheric aerosol particles are recognized as an important contributor to climate change, but the magnitude of their radiative forcing as well as its sign is highly uncertain (IPCC, 2007)
It can be seen from the mean MAX-DOAS data that the correlations of k476(1–2 km) values tend to deviate from linearity at higher lidar values (Fig. 3b)
MultiAxis Differential Optical Absorption Spectroscopy (MAXDOAS) and lidar k354(0–1 km) values are correlated linearly, a linear regression analysis suggests that MAX-DOAS values are systematically smaller

Summary

Introduction

The present study is a follow-on to that of Irie et al (2008a), who first reported ground-based MAX-DOAS measurements of the vertical profile of the aerosol extinction coefficient at a single wavelength of 476 nm (k476) at Tsukuba, Japan (36.1◦ N, 140.1◦ E, 29 m a.s.l.), from 1 November to 21 December 2006 They concluded that the overall uncertainties of MAX-DOAS k476 values at 0–1 and 1–2 km are better than 30% and 60%, respectively, based on comparisons with other established aerosol measurements by lidar and sky radiometer, part of the differences found in the comparisons should have been caused by the Published by Copernicus Publications on behalf of the European Geosciences Union. To characterize MAX-DOAS aerosol measurements in a more robust sense, we present retrievals of the aerosol extinction coefficient at an additional, shorter wavelength, 354 nm (k354), and discuss them together with the retrievals at 476 nm

MAX-DOAS measurements

Lidar and sky radiometer measurements

Results and discussion

Conclusions