Kwanchul Kim

Retrieval of the Single Scattering Albedo of Asian Dust Mixed with Pollutants Using Lidar Observations

The vertical distribution of single scattering albedos (SSAs) of Asian dust mixed with pollutants was derived using the multi-wavelength Raman lidar observation system at Gwangju (35.10°N, 126.53°E). Vertical profiles of both backscatter and extinction coefficients for dust and non-dust aerosols were extracted from a mixed Asian dust plume using the depolarization ratio from lidar observations. Vertical profiles of backscatter and extinction coefficients of non-dust particles were input into an inversion algorithm to retrieve the SSAs of non-dust aerosols. Atmospheric aerosol layers at different heights had different light-absorbing characteristics. The SSAs of non-dust particles at each height varied with aerosol type, which was either urban/industrial pollutants from China transported over long distances at high altitude, or regional/local pollutants from the Korean peninsula. Taking advantage of independent profiles of SSAs of non-dust particles, vertical profiles of SSAs of Asian dust mixed with pollutants were estimated for the first time, with a new approach suggested in this study using an empirical determination of the SSA of pure dust. The SSAs of the Asian dust-pollutants mixture within the planetary boundary layer (PBL) were in the range 0.88–0.91, while the values above the PBL were in the range 0.76–0.87, with a very low mean value of 0.76±0.05. The total mixed dust plume SSAs in each aerosol layer were integrated over height for comparison with results from the Aerosol Robotics Network (AERONET) measurements. Values of SSA retrieved from lidar observations of 0.92±0.01 were in good agreement with the results from AERONET measurements.

Utilization of the depolarization ratio derived by AERONET Sun/sky radiometer data for type confirmation of a mixed aerosol plume over East Asia

ABSTRACT This article confirms the utilization of depolarization ratio derived by ground-based Aerosol Robotic Network (AERONET) Sun/sky radiometer data obtained during a high-PM10 episode at Gwangju, Korea (35.10° N, 126.53° E) in April 2009, in order to determine the nature and source of the atmospheric aerosol associated with this event. Integrated monitoring using satellite and depolarization light detection and ranging (lidar) data, together with model analysis, was also completed for the period of the high-PM10 event. The Sun/sky radiometer-derived particle depolarization ratio values are similar to the lidar-derived values, and these values highlight the effect of dust particles on aerosol observation. High particle depolarization ratios (12.5–14.2%) were observed when the aerosol plume transported from the west between 5 and 7 April. In contrast, lower particle depolarization ratios (5.8–9.8%) were detected when the aerosol plume was transported from the north on other observation days. Different optical properties are also shown according to the variation of depolarization ratio. High values in the real part of the refractive index (1.47–1.49 at 440 nm), lower values in the imaginary part of the refractive index (0.007–0.009 at 440 nm), and a high proportion of coarser particles were observed during the high depolarization ratio period. In contrast, the atmospheric aerosol transported from the north showed characteristics more commonly associated with smoke, with lower values in the real part of the refractive index (1.41–1.48 at 440 nm), higher values in the imaginary part of the refractive index (0.008–0.011), and a high proportion of fine particles. This indicates that the Sun/sky radiometer-derived depolarization ratio is a useful parameter when estimating the effect of dust particles during high-PM10 events.

On the spectral depolarisation and lidar ratio of mineral dust provided in the AERONET version 3 inversion product

Knowledge of the particle lidar ratio ( Sλ) and the particle linear depolarisation ratio ( δλ) for different aerosol types allows for aerosol typing and aerosol-type separatio n in lidar measurements. Reference values generally origina te from dedicated lidar observations but might also be obtaine d 5 from the inversion of AERONET sun/sky radiometer measurements. This study investigates the consistency of spec tral Sλ andδλ provided in the recently released AERONET version 3 inversion product for observations of undiluted mineral dust in the vicinity of major deserts: Gobi, Sahara, Ara 10 bian, Great Basin and Great Victoria deserts. Pure dust conditions are identified by an Ångstöm exponent < 0.4 and a fine-mode fraction< 0.1. The values of spectral Sλ are found to vary for the different source regions but generally show an increase with de15 creasing wavelength. The feature correlates to AERONET retrieving an increase in the imaginary part of the refractive index with decreasing wavelength. The smallest values of Sλ = 35− 45sr are found for mineral dust from the Great Basin desert while the highest values of 50-70 sr have been 20 inferred from AERONET observations of Saharan dust. Values ofSλ at 675, 870, and 1020 nm seem to be in reasonable agreement with available lidar observations while those at 440 nm are up to 10 sr higher than the lidar reference. The spectrum ofδλ shows a maximum of 0.26-0.31 at 1020 nm 25 and decreasing values as wavelength decreases. AERONETderivedδλ at 870 and 1020 nm are in line with the lidar reference while values of 0.19-0.24 at 440 nm are smaller than the independent lidar observations by a difference of 0.03 t o 0.08. This general behaviour is consistent with earlier stu dies 30 based on AERONET version 2 products.