Report of Group 2: Lev Labzovskii, Anna Nikandrova, Robert Banks, Juan Antonio Bravo Aranda, Xinxin Li

Aerosols are an important contributor to the global climate system. Quantifying their contribution to the total anthropogenic radiative forcing is still a major challenge (IPCC, 2013). It can be difficult to understand and determine the type, size, and distribution of aerosols in the lowest layers of the atmosphere. In this study we attempt to synergize the strengths of several instruments to characterize aerosols in the PBL, namely a multiwavelength lidar system and an aerosol mass spectrometer (AMS).

Data was measured and collected from the instruments during the 1^st ITaRS Summer School in Bucharest, Romania from the 24-28 September, 2013. The 26^th of September had the most complete dataset from all the associated instruments and provided an interesting case to investigate. Ancillary information was provided by NOAA HYSPLIT, MODIS fire maps, and AERONET sun photometer.

First, we evaluated data from the multiwavelength lidar. Lofted aerosol layers (LAL) were detected in the free troposphere (FT) from 08:25-15:00 UTC. From 10:15-12:22 UTC LAL stay in the FT during the development of the PBL. Then a mixture between the LAL and the PBL appears around 13:00 UTC leading to a possible detection of FT at the surface.

Next, we decided to separate the period of interest into 2 stages. In the first stage (08:00-12:00 UTC) the aerosol load was well-stratified and the PBL development was in progress. In the second stage (12:00-19:00 UTC) the aerosol load had become more homogeneous and the PBL had reached a maximum height. The two stages observed with the lidar can also be distinguished with the AMS.

A synergistic relationship between the lidar and AMS can be seen in Figure 1. In stage 1 mentioned above there was a slow increase of organic and sulfate particles noted by the AMS. However, stage 2 can be further sub-divided into 2 unique cases according to a higher slope increase and concentration of the organics and sulfates. After reviewing in-situ indicators from the AMS case 1 (12:00-16:00 UTC) can be identified as dominated by aged biomass burning aerosols (BBA) and case 2 (16:00-19:00 UTC) can be distinguished by the occurrence of less-aged BBA. Furthermore, Raman lidar inversion and microphysical properties support the same results.

In summary, the temporal evolution of the lidar signals indicates the entrainment of the LAL to the PBL due to convective turbulence processes. BBA was detected by means of lidar and AMS during the 26th September 2013. Different states of oxidation process of the BBA at ground-level were distinguished through AMS data analysis.The Raman and microphysical retrievals indicate the presence of BBA. However, we are physically constrained to link this value with the non-local or local BBA. Finally, it is shown that synergistic combination of lidar and AMS through the exploitation of other instruments as ancillary information can be useful for better understanding the complexity of aerosol distribution.

Acknowledgements: Many thanks to J. Vasilescu, D. Nicolae, L. Belegante, A. Nemuc, D. Müller and C. Talianu. We greatfully acknowledge to ITaRS (FP7-PEOPLE-2011-ITN under grant 289923), Finnish Centre of Excellence 1141135 and the grant AP2009-0559 for the funding. The authors acknowledge the NOAA Air Resources Laboratory (ARL) for the provision of the HYSPLIT transport and dispersion model.

Figure 1. Temporal evolution of the lidar range-corrected signal at 532 nm (color map) and of the concentrations of organic elements (green dots) and sulfates (red dots) from AMS at Bucharest on 26^th September, 2013.