Characterization of aerosol over the Eastern Mediterranean by polarization sensitive Raman lidar measurements during A-LIFE – aerosol type classification and type separation

Kurzfassung

Aerosols are key players in Earth’s climate system, with mineral dust being a major component of the atmospheric aerosol load. While former campaigns focused on investigating the properties and effects of layers of rather pure mineral dust, the A-LIFE (Absorbing aerosol layers in a changing climate: aging, lifetime and dynamics) campaign in April 2017 aimed to characterize dust in complex aerosol mixtures. In this study we present ground-based lidar measurements that were performed at Limassol, Cyprus, in April 2017. During our measurement period, the measurement site was affected by complex mixtures of dust from different sources and pollution aerosols from local as well as long-range transported sources. Considering the lidar measurements from two ground-based systems, POLIS (portable lidar system) and PollyXT (portable lidar system with extended capabilities). We found mean values and mean systematic errors (standard deviation, SD, given in brackets) of the particle linear depolarization ratio and extinction-to-backscatter ratio (lidar ratio) of 0.26 ± 0.03 (SD of 0.02) and 41 ± 5 sr (SD of 3 sr) at 355 nm and of 0.29 ± 0.02 (SD of 0.02) and 38 ± 5 sr (SD of 6 sr) at 532 nm for Arabian dust and of 0.26 ± 0.03 (SD of 0.03) and 55 ± 8 sr (SD of 6 sr) at 355 nm and of 0.28 ± 0.02 (SD of 0.01) and 54 ± 8 sr (SD of 8 sr) at 532 nm for Saharan dust. The values found for pollution aerosols of the particle linear depolarization ratio and the lidar ratio are 0.06 ± 0.02 (SD of 0.04) and 64 ± 13 sr (SD of 5 sr) at 355 nm and of 0.04 ± 0.02 (SD of 0.01) and 64 ± 12 sr (SD of 4 sr) at 532 nm, respectively. We use our measurements for aerosol typing and compare them to aerosol typing from sun photometer data, in situ measurements, and trajectory analysis. The different methods agree well for the derived aerosol type, but looking at the derived dust mass concentration from different methods, the trajectory analysis frequently underestimates high dust concentrations that were found in major mineral dust events.