Analysis of equivalent black carbon multi-year data at an oil pre-treatment plant: Integration with satellite data to identify black carbon transboundary sources

This study analyzes a multi-year dataset of equivalent black carbon (EBC) concentration collected in 2012-2015 by a 7-wavelengths Aethalometer at Centro Olio Val d'Agri (COVA) in southern Italy, which is the largest European oil pre-treatment plant. These data, together with the local air circulation analysis, were used to identify the black carbon (BC) sources in Agri valley, specifically the COVA plant and vehicular traffic. During a limited period of 2012-2013, simultaneous measurements of PM10 concentration were available for comparison with the EBC data, which revealed correlation values of 0.31-0.43 between PM10 and EBC indicating a relevant contribution of BC to particulate matter at the site. On average, EBC/PM10 ratio is 7%, a value equal to that found at an urban-background site in Rome measured during non-rush hours. Moreover, an ad hoc procedure combining EBC data, Hybrid Single-Particle Lagrangian Integrated Trajectory back-trajectories (HYSPLIT), and satellite fire data enabled detection of days affected by the transport of carbonaceous particles. Both Visible Infrared Imaging Radiometer Suite (VIIRS) and Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data were used as input for the algorithm, and the corresponding results were compared and discussed. VIIRS showed a better performance in detecting smaller/cooler hotspots especially in cases of flaring, as observed during flaring events at the COVA plant itself. Application of the procedure suggests that both regional and non-regional biomass burning episodes, which occur mainly during summer, could contribute to the BC load at the site. The approach applied to the case study of the present work can be useful for estimating the relative contributions of local and remote sources of BC.