Biomass burning aerosols in the southern hemispheric midlatitudes as observed with a multiwavelength polarization Raman lidar

Abstract. In this paper, we present long-term observations of the multiwavelength Raman lidar PollyXT conducted in the framework of the DACAPO-PESO campaign. Regardless the relatively clean atmosphere in the southern mid-latitude oceans region, we observed regularly events of long-range transported smoke, originating either from regional sources in South America or from Australia. Two case studies will be discussed. Both cases were identified as smoke events and they occurred on 5 February 2019 and 11 March 2019. 5 For the first case considered, the lofted smoke layer was located at an altitude between 1 and 4.2 km, and apart from the predominance of smoke particles, particle linear depolarization values indicated the presence of dust particles in the layer. Mean lidar ratio values at 355 and 532 nm were 49 ± 12 and 24 ± 18 sr respectively, while the mean particle linear depolarization was 7.6 ± 3.6 % at 532 nm. The advection of smoke and dust particles above Punta Arenas affected significantly the available CCN and INP in the lower troposphere, and triggered effectively ice crystal formation processes. Regarding the second case, the thin smoke layers were observed at altitudes between 5.5–7, 9 and 11 km. The particle linear depolarization ratio at 532 nm increased rapidly with height, starting from 2 % for the lowest two layers and increasing up to 9.5 % for the highest layer, indicating the possible presence of non-spherical coated soot aggregates. INP activation was effectively facilitated. The long-term analysis of the one year of observations showed that tropospheric smoke advection over Punta Arenas occurred 16 times (lasting from 1 to 17 hours), regularly distributed over the period and with high potential to influence cloud formation in the otherwise pristine environment of the region.