Report Group 3: Athina Argyrouli, Lukas Pfitzenmaier, Marco Rosoldi, Stefanos Samaras, Xiaoli Zhou

The objective of this study is to identify the aerosol type by synergistically using lidar and microwave radiometer data. The possible aerosol type retrieved by the optical properties of aerosols is further compared with the aerosol type as provided by a model. The multi-wavelength Raman lidar system of the National Institute for Research and Development in Optoelectronics (INOE), located in Magurele (Bucharest), allows us to retrieve the vertical profiles of aerosol optical properties: extinction and backscatter coefficients at 355 and 532nm; lidar ratio at 355 and 532nm, particle depolarization ratio at 532nm and Angstroem coefficients.

The investigated case study refers to night measurement on 28/09/2013. Homogeneous aerosol layers were identified between 1.5 and 2.5 km of altitude from 17:50 UTC to 19:00 UTC. The vertical profiles of aerosol optical properties have been retrieved by processing the lidar signals averaged on that time window. The mean values of intensive aerosol optical properties related to the aerosol layer between 1.9 and 2.3km of altitude are reported in table 1. Such values are compatible with the presence of mixed urban haze and fresh/aged smoke particles or forest fire smoke in free troposphere (Muller et al., JGR, 2007). This seems to be confirmed by the analysis of the back-trajectories calculated from the NOAA Hysplit Model, showing the air masses related to the selected aerosol layer to originate from Canada.

In addition, relative humidity profiles within the troposphere were retrieved by a microwave radiometer (MWR) aiming to investigate the influence of relative humidity (RH) on the aerosol optical properties and thus, the hydroscopic behavior of aerosols. The retrieved values of the microwave radiometer between 1.9 and 2.3 km height were 60% RH and stable over the height interval.

OPAC (Optical Properties of Aerosols and Clouds) provides optical properties in the solar and terrestrial spectral range of atmospheric particulate matter. OPAC has two inputs, the number of iteration and the relative humidity of the aerosol layer. For a specific aerosol type, the iteration starts from the minimum value of its critical component to the maximum by taking user-defined number of steps (from 1 to 10). In this study, the number of iteration is fixed at 10. By adjusting the relative humidity, it is possible to simulate the lidar ratio and the angstrom exponent profiles of different aerosol types with respect to the given relative humidity (Fig 1).

The initial typing of aerosols as smoke, urban haze or polluted continental was based on the aerosol optical properties which were retrieved by the lidar data with respect to the corresponding meteorology. This is further confirmed from lidar ratio and Angstrom exponent as a function of RH when calculated from OPAC model.