Clear‐column radiative closure during ACE‐Asia: Comparison of multiwavelength extinction derived from particle size and composition with results from Sun photometry

Abstract

, aerosol size distributions and chemical compositions were measured using differential mobility analyzers (DMA), an aerodynamic particle sizer (APS), Micro-Orifice Uniform Deposit Impactors (MOUDI), and denuder samplers onboard the Twin Otter aircraft as part of the Aerosol Characterization Experiment (ACE)-Asia campaign. Of the 19 research flights, measurements on four flights that represented different aerosol characteristics are analyzed in detail. Clear-column radiative closure is studied by comparing aerosol extinctions predicted using in situ aerosol size distribution and chemical composition measurements to those derived from the 14-wavelength NASA Ames Airborne Tracking Sun photometer (AATS-14). In the boundary layer, pollution layers, and free troposphere with no significant mineral dust present, aerosol extinction closure was achieved within the estimated uncertainties over the full range of wavelengths of AATS-14. Aerosol extinctions predicted based on measured size distributions also reproduce the wavelength dependence derived from AATS-14 data. Considering all four flights, the best fit lines yield Predicted/Observed ratios in boundary and pollution layers of 0.97 ± 0.24 and 1.07 ± 0.08 at l = 525 nm and 0.96 ± 0.21 and 1.08 ± 0.08 at l = 1059 nm, respectively. In free troposphere dust layers, aerosol extinctions predicted from the measured size distributions were generally smaller than those derived from the AATS-14 data, with Predicted/Observed ratios of 0.65 ± 0.06 and 0.66 ± 0.05 at 525 and 1059 nm, respectively. A detailed analysis suggests that the discrepancy is likely a result of the lack of the knowledge of mineral dust shape as well as variations in aerosol extinction derived from AATS-14 data when viewing through horizontally inhomogeneous layers.

Measurements of aerosol size‐resolved hygroscopicity at sub and supermicron sizes

“…Most components of this package have been described in previous publications [cf. Hegg et al, 2002;Wang et al, 2002]. However, the principal instrument utilized, the AHS, is new and, while a detailed description will be forthcoming, we present the key features of this instrument relevant to the current discussion here.…”

Aerosol Properties Computed from Aircraft-Based Observations During the ACE-Asia Campaign: 2. A Case Study of Lidar Ratio Closure

“…The left panel of Figure 1 shows the extinction profile derived by Schmid et al (2003) from the sunphotometer measurements, and boundaries between three distinct layers observed: marine boundary, pollution, and dust layer, all with different particle physical and chemical characteristics. The backtrajectory analysis showed that the pollution layer originated from mainland China (Wang et al 2002).…”

“…The details about aerosol optical depth and size distribution measurements are given by Schmid et al (2003) and Wang et al (2002), respectively. In brief, aerosol optical depth was measured at 13 wavelengths, in the wavelength range from 0.354 μm to 1.558 μm, using the 14-channel NASA Ames Airborne Suntracking Sunphotometer (AATS-14).…”

“…For aerosol chemical composition measurements, 8 MicroOrifice Uniform Deposit Impactors (MOUDI) and 3 denuder samplers operated aboard the Twin Otter aircraft (Wang et al 2002). Although each MOUDI had 5 stages, only one of them (collecting particles with diameters up to 3 μm) was in operation.…”

“…In the present work, the aerosol extinction spectra are used for the retrieval of the vertical profile of aerosol size distribution. At the same time size distribution measurements were made using a combination of a Differential Mobility Analyzer (DMA) System, for measurements in the 0.015-1.0 μm particle diameter range, and an Aerodynamic Particle Sizer (APS) for the 0.5-10 μm diameter range (Wang et al 2002).…”