We are deploying different types of mass spectrometers to simultaneously monitor all the steps leading to SOA formation starting from the emissions of VOCs. The composition of VOCs is measured with the Proton Transfer Reaction Time of Flight mass spectrometer (PTR-ToF). The composition of HOMs is measured with an iodide adduct Chemical Ionization Mass Spectrometer (I-CIMS) and a nitrate CIMS covering a wide range of HOM volatilities. Finally, the composition of SOA is measured with a Filter Inlet for Gases and AEROsols (FIGAERO) mounted in front of the I-CIMS and the superior Aerosol Mass Spectrometer (AMS) that can also provide size segregated information about the chemical composition of the particles.

The measurements are conducted both in the field and the laboratory. The laboratory experiments are done using flow tubes and smog chambers. The recent laboratory studies have been focusing on the effect of temperature, NOx, Cl-radical and seed aerosol properties on HOM and SOA. The field measurements have been conducted at SMEAR-II station (https://www.atm.helsinki.fi/SMEAR/index.php/smear-ii) in a boreal forest in Southern Finland. The station is well known from its comprehensive measurements. The recent field-focus has been on reactive nitrogen species, vertical profiles of HOM and Positive Matrix Factorization (PMF) analysis on mass spectrometer data.