10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Spatio-Temporal Variability of Aerosol Physical and Optical Properties from Mobile In-Situ Measurements in the Po Valley (Italy) during Summertime
MICHELE BERTÓ, Rosaria Erika Pileci, Robin Modini, Stefania Gilardoni, Angela Marinoni, Douglas Orsini, Matteo Rinaldi, Martin Gysel, Paul Scherrer Institute
Abstract Number: 171 Working Group: Aerosol Physics
Abstract Characterizing the spatio-temporal variability of atmospheric aerosols in terms of physical and optical properties is of great importance in evaluating their climatic and health effects. Black carbon (BC) particles have mainly anthropogenic origin and they are the main light absorbing component of the atmospheric aerosol. BC has the second largest positive radiative forcing value (RF), but with an uncertainty of 90%. A still poor knowledge of the mass absorption cross-section (MAC, the ratio between the absorption coefficient and the mass concentration of BC) spatio-temporal variability, absolute value and its behaviour in terms of coating absorption enhancement, significantly contribute to BC RF uncertainties.
To investigate the BC MAC variability and its relations with other aerosol physical and optical properties, a field campaign (“Actris-2 - Mt. Cimone and Po valley field campaign 2017”) was carried out in July by using a mobile pollutants measurement laboratory equipped with several scientific instruments, among others a Single Particle Soot Photometer (SP2, DMT) and a Multiangle Absorption Photometer (MAAP, Thermofisher). Four environmental pollutants regimes were characterized: urban traffic (streets), urban background (CNR, Bologna), rural areas and a high altitude location (Mt. Cimone).
A MAC diurnal cycle was observed during stationary measurement at CNR: MAC minimum occurring in the morning when fresh traffic emissions dominated, maximal values in the afternoon when BC mass was dominated by aged particles. The coating-induced lensing effect is the hypothetical explanation for the MAC increase. Traffic emissions were an important factor in explaining the variability in MAC values during the mobile measurements causing a decrease in the MAC absolute values, otherwise generally stable due to the mostly aged particles in the Po Valley troposphere. Further quantitative investigation of BC core/coating diameters is planned to provide a clearer explanation of the MAC variability.