Fine particles affect climate change in complex ways that are not fully understood and were verified to be harmful to animal and human health. For these reasons information concerning their composition is important to understand their behaviour and to elaborate strategies to mitigate air pollution in urban environments.
The overall objective of this study was to investigate in more detail chemical characteristics of ambient particulate matter (PM) and its sources. Studies made in laboratory and during field were used to study composition of fresh emissions, changes during aging, and finally composition of submicron PM (PM1) observed in ambient air. For that the field studies were performed at three different sites: rural, urban, and background urban with the HR-ToF-AMS and ACSM, instruments that measured only the non-refractory PM1 (NR-PM1). For this reason the new SP-AMS was further characterized in order to evaluate its feasi-bility to detect trace metals.
The use of the positive matrix factorization (PMF) has shown useful in the identification of PM sources. Thus, the PMF was applied to the mass spectrometers datasets and 11 different components of the organic aerosol (OA) were identified, 6 types of oxygenated OAs (OOAs), one containing substantial organosulfate fragments from methanesulfonic acid (MSA), long-range transported biomass burning OA (LRT-BBOA), nitrogen-containing OA (NOA), local BBOA, coffee roastery OA (CROA), and hydrocarbon-like OA (HOA). The last three most likely represented the primary organic aerosol (POA), while the others represented the secondary OA (SOA). The OM was dominated by aerosol particles of secondary origin (65%).
The investigation of different properties of the PM1 revealed more information about its composition and sources. A comparison of the AMS data with those from additional instrumentation indicated that most of the PM1 was non-refractory. The water-solubility of the OM indicated that the low-volatility OOA (LV-OOA) and the LRT-BBOA were the most water-soluble components. The SV-OOA presented clear semi-volatile character when investigated as a function of the local air temperature, decreasing in concentration with the air temperature increase. Concerning the aerosol neutralization, in most sites the results indicated enough ammonium to neutralize the major inorganic anions, except for Helsinki during wintertime when the aerosol particles were acidic most of the time. The size-resolved chemical composition was investigated in detail to different episodes and revealed internally and externally mixed aerosol particles in two different modes, an accumulation (~470 nm) and a lower mode (~130nm). The different modes were composed of different compounds and suggested a rather acidic lower mode mainly dominated by nitrate most likely from local traffic emissions. The laboratory experiments accomplished with the SP-AMS successfully confirmed the feasibility of detection of trace metals. 13 different metals were identified through the determination of isotopic patterns. Furthermore, the negative mass defect, typical from metals, was observed useful in their identification in the mass spectrum. The measurement of trace metals by the SP-AMS represents a step forward in the study of sources and might be extremely useful in the next source apportionment studies
