3 4 K. Sebastian Schmidt, Peter Pilewskie, Bernhard Mayer, Manfred Wendisch, 5 Bruce Kindel, Steven Platnick, Michael D. King, Gala Wind, G. Tom Arnold, 6 Lin Tian, Gerald Heymsfield, Heike Eichler 7 8 9 10 11 12 1 University of Colorado, Boulder, CO, USA 13 2 Deutsches Zentrum für Luftund Raumfahrt (DLR), Oberpfaffenhofen, Germany 14 3 Ludwig-Maximilians-Universität, München, Germany 15 4 Universität Leipzig, Germany 16 5 Goddard Space Flight Center, Greenbelt, MD, USA 17 6 SSAI, Inc., Lanham, MD, USA 18 7 Universität Mainz, Germany 19 20

The aerosol mixing state was investigated with an optical closure study at Xinken, Pearl River Delta of China in 2004. On the basis of in situ aerosol microphysical and chemical measurements and a two‐component aerosol optical model an internal consistency algorithm was developed to model the mass ratio (r) of externally mixed elemental carbon (EC) to total EC, which minimized the discrepancies between measured and calculated optical properties. The rest of EC was assumed to be internally mixed. A time series ofrwas retrieved. Good agreement between model and observation was found, on the order of ±15% for total/back scattering coefficients and ±10% for absorption coefficient. The EC mixing state was strongly dependent on the local wind patterns. When north/northeasterly winds prevailed, the air came from the urban and industrial areas of mainland China, and EC was mainly externally mixed with an averagerof 85 ± 12%. When the airflow was controlled by a weak local wind system, the mixing state showed a pronounced diurnal variation. During daytime the wind speed was nearly zero. This favored the increase of local pollution, and the averagerwas about 95%. However, during nighttime the EC mixing state transformed to be internally mixed apparently with an averagerof 53 ± 15%, which can be explained by a more aged air mass. The south/southeasterly winds coming from the sea were found to have the most important effect on the transformation of EC mixing state in the night, but fairly rapid local aging processing was also observed. The uncertainties of the model were explored by a Monte Carlo simulation.

Simulation studies were carried out with regard to the feasibility of using combined observations from sunphotometer (SPM) and lidar for microphysical characterization of aerosol particles, i.e., the retrieval of effective radius, volume, and surface-area concentrations. It was shown that for single, homogeneous aerosol layers, the aerosol parameters can be retrieved with an average accuracy of 30% for a wide range of particle size distributions. Based on the simulations, an instrument combination consisting of a lidar that measures particle backscattering at 355 and 1574 nm, and a SPM that measures at three to four channels in the range from 340 to 1020 nm is a promising tool for aerosol characterization. The inversion algorithm has been tested for a set of experimental data. The comparison with the particle size distribution parameters, measured with in situ instrumentation at the lidar site, showed good agreement.