European pollution outbreaks during ACE 2 : Microphysical particle properties and single-scattering albedo inferred from multiwavelength lidar observations

Abstract

We present vertically resolved physical particle properties and the single-scattering albedo at 532 nm of pollution plumes advected from the European continent out over the Atlantic Ocean. The parameters follow from the inversion of optical data, which were obtained from six-wavelength aerosol lidar observations near Sagres (37degreesN, 9degreesW), Portugal, in the framework of Aerosol Characterization Experiment 2 (ACE 2) (June-July 1997). Particle effective radii were 0.15 +/- 0.06 m m, volume concentrations ranged from 6 to 27 mum(3) cm(-3), and surface area concentrations were 80 to 1200 mum(2) cm(-3). The particles in general showed negligible absorption, with the mean imaginary part of the wavelength-independent complex refractive index being at 0.009i +/- 0.010i. The mean real part was 1.56 +/- 0.07. A mean value of 0.95 +/- 0.06 was obtained for the single-scattering albedo at 532 nm. The numbers indicate that the major contributor to the observed pollution was nonabsorbing ammonium-sulfate-like material. A very small fraction was contributed by absorbing sootlike material. Correlation analysis showed that effective radius was well correlated with the Angstrom exponents of the underlying extinction spectra. Furthermore, correlations of the single-scattering albedo with the particle extinction-to-backscatter ratio and with the imaginary part of the complex refractive index were found. This result shows that the first two parameters contain information about the chemical state of the observed particles.