Chemical Aging of Urban Aerosol: The POSEIDON-2024 Campaign
Christina N. Vasilakopoulou, ANGELIKI MATRALI, Andreas Aktypis, Christos Kaltsonoudis, Katerina Seitanidi, Kalliopi Florou, Georgia A. Argyropoulou, Maria Georgopoulou, Aikaterini Bougiatioti, Nikolaos Mihalopoulos, Spyros Ν. Pandis, FORTH Institute of Chemical Engineering Sciences
Abstract Number: 154
Working Group: Source Apportionment
Abstract
An intensive month-long campaign was conducted in September 2024 in the island of Poros, 50 km downwind of Athens. The major goal of the POSEIDON campaign was the quantification of the chemical aging of urban organic aerosol (OA) transported for hours over the sea, during a photochemically active period. The campaign included high-temporal resolution measurements of organic vapors (VOCs/IVOCs), OA and its chemical components, along with offline analysis of daily samples of both gaseous and particulate species. Measurements in Poros were combined with those of urban supersites in Athens (in Thissio and Demokritos).
PM1 was modest (9.6 μg m-3), primarily comprised of OA (50%) followed by sulfate (35%), black carbon (9%) and ammonium (6%). Nitrates were less than 1% since warm conditions (25±3oC) favored volatilization of ammonium nitrate and rapid decomposition of organonitrates. Positive Matrix Factorization of the observed highly oxidized OA (O:C=0.77±0.08) AMS spectra yielded a three-factor solution. The two highly oxidized factors, more oxidized MO-OOA (64%) and less oxidized LO-OOA (29%) dominated, with a 7% contribution by hydrocarbon-like OA (HOA). The MO-OOA was related to aged biomass burning OA, indicated by its correlation to potassium, acetonitrile, and glycolic acid levels. LO-OOA was related to both anthropogenic (e.g., toluene) and biogenic (e.g. pinonaldehyde) organic vapors. PM2.5 toxicity metrics in the small island were comparable to those in Athens’ center.
The surprisingly frequent (70%) appearance of 20-30 nm mode particles (absent from Athens) suggested strong nucleation/growth over the Saronic Gulf downwind of Athens. Τhe role of SO2 sources (industry, shipping) as well as sources of ammonia/amines and biogenic VOCs in new particle formation was explored. OA’s photochemical age, estimated with various techniques (photochemical clocks, Lagrangian modeling, etc.), was related to its composition. Results are compared to aging rates assumed in current chemical transport models.