1. Online measurements of chemical composition and size distribution of submicron aerosol particles in east Baltic region Inga Rimšelytė Institute of Physics Vilnius, Lithuania

2. 2 Research interests: The continuous study of these aerosol particles concentration, size and chemical composition is therefore imperative for better understanding the environmental effects of the atmospheric particles, as well as their sources, formation and transformation processes. PM, especially the fine fraction, remains airborne for long time in the atmosphere and can travel for hundreds or even thousands of kilometers. Owing to chemical reactions, condensation and accumulation, the particle change their chemical composition, mass and size. The fact that PM can travel over such long distances implies that pollutants emitted in one European country can affect PM concentration in neighboring countries and even countries far distant from the source.The continuous study of these aerosol particles concentration, size and chemical composition is therefore imperative for better understanding the environmental effects of the atmospheric particles, as well as their sources, formation and transformation processes. PM, especially the fine fraction, remains airborne for long time in the atmosphere and can travel for hundreds or even thousands of kilometers. Owing to chemical reactions, condensation and accumulation, the particle change their chemical composition, mass and size. The fact that PM can travel over such long distances implies that pollutants emitted in one European country can affect PM concentration in neighboring countries and even countries far distant from the source. The chemical complexity and labile nature of atmospheric particulate matter strongly favor real-time instrumental analysis techniques that characterize pertinent physical and chemical properties without having to collect, store, and transport samples.The chemical complexity and labile nature of atmospheric particulate matter strongly favor real-time instrumental analysis techniques that characterize pertinent physical and chemical properties without having to collect, store, and transport samples. Real-time instruments that characterize the chemical composition of atmospheric PM, ideally as a function of particle size, are a more recent development.

3. 3 The aim of this study was to The aim of this study was to investigate and provide insights into the sources and characteristics of submicron aerosols through analysis of their size distribution, the temporal variations of submicron particle compositions, and the estimation of air mass transport.

4. 4 Fig.1. Geographycal location of the station. Preila 55 o 55’N; 21 o 00’E Sector 1 represent air masses from the North Atlantic Ocean, the Norwegian sea and Scandinavia, supposedly, a clean sector, were sector 3 (East Europe) and 5 (Western and Southern Europe) were initially classified as polluted sectors characterized different types of pollution. Buffer sectors help to separate different regions since it was often impossible to attribute air mass to solely one of major sector.

5. 5 Fig. 2. Aerosol mass spectrometer scheme The AMS, developed by Aerodyne Research Inc., provides on-line quantitative measurements of the chemical composition and size distributions of the non- refractory fraction of submicron aerosol particles (approximately PM1.0).

6. 6 Table 1. Main ion fragments used to identify inorganic and organic aerosol species in AMS spectra. Quantitative particle collection efficiency (about 100%) in the range of 60 to 600nm in diameter. Collection extends to particles about a factor of 2-3 smaller and larger with reduced efficiency. The AMS does not characterize individual organic molecules in ambient air. This technique quantifies two types of organic aerosols, hydrocarbon-like and oxygenated (HOA and OOA, respectively), which together account for almost all the organic aerosol mass measured by the AMS.

7. 7 Fig. 3. Mass concentration (μg·m -3 ) of nitrate, sulfate, ammonium, organic compounds, and total aerosol mass Fig. 3. Mass concentration (μg·m -3 ) of nitrate, sulfate, ammonium, organic compounds, and total aerosol mass.

8. 8 Fig. 5. Mass fraction of sulfate and organic compounds to the total aerosol mass concentration measured by AMS at Preila. Fig. 6. Correlation between sulfate and organic compounds: a) in clean air mass; b) in polluted air mass.

9. 9 Fig. 8. Time series of nitrate, sulfate, and organic mass concentration for the whole campaign, together with time series of the mode diameter of these species. Comparison of the time series of modes of the size distributions of the individual species and their mass concentrations shows a significant relationship between these quantities Based on results from the mass concentration measurements, the pollution events are primarily related to regional transport rather than to intense local production. This suggests that the aerosol observed during these events is dominated by aged aerosol that has been transported to the site and is consistent with the observed larger mode diameter size distributions. During times of low total mass concentrations, the locally produced fraction of young and small particles play a larger role in the aerosol size distribution, shifting the mode diameter to smaller sizes. Comparison of the time series of modes of the size distributions of the individual species and their mass concentrations shows a significant relationship between these quantities. Based on results from the mass concentration measurements, the pollution events are primarily related to regional transport rather than to intense local production. This suggests that the aerosol observed during these events is dominated by aged aerosol that has been transported to the site and is consistent with the observed larger mode diameter size distributions. During times of low total mass concentrations, the locally produced fraction of young and small particles play a larger role in the aerosol size distribution, shifting the mode diameter to smaller sizes.

10. 10 Fig. 9. Size distribution of sulfate and organic aerosol fractions: a) in air mass from the North Atlantic Ocean; b) in air mass from Southern Europe

11. 11 The derived mass spectrum demonstrates close similarity in the overall pattern with those of aged/oxidized organic aerosols in rural areas. The mass spectrum obtained in a comparatively clean period is similar to that obtained in a polluted period but differs in a number of ways.

12. 12 Conclusions: The major observed components of the aerosol particles (PM1) were sulfate and organic compounds. Large contribution of organic matter was established in all air masses, and it reached 60 % of the total aerosol particle mass in the clear Atlantic air masses. The size distribution of sulfate-containing particles and organic-containing particles in the accumulation mode differed in shape and had a mode diameter of about 340 nm and 190 nm, respectively. This difference implies that species were externally mixed. In polluted air masses the size distribution of sulfate-containing particles and organic-containing particles was similar, the modal peaks of the sulfate and organic compounds were equal, showing that chemical species were internally mixed. Dominant mass fragments m/z = 44 coupled with m/z 18 in the organic fraction indicate that aerosol is aged. The mass spectra of the organic fraction in clean and polluted periods show different fragmentation. These changes may well reflect the change in the source.

13. 13 Take home messages Ratios of CO to EC are used to determine the influences of anthropogenic activity on aerosol composition. Low OC/EC ratios indicate anthropogenic influences on aerosol composition due to the larger fraction of combustion derived elemental carbon.Ratios of CO to EC are used to determine the influences of anthropogenic activity on aerosol composition. Low OC/EC ratios indicate anthropogenic influences on aerosol composition due to the larger fraction of combustion derived elemental carbon. More than 50% of organic compounds of the total aerosol mass was found in the fine aerosol fraction, while 23–44% was in the coarse particles. This difference can be explain by difference particles formation mechanisms.More than 50% of organic compounds of the total aerosol mass was found in the fine aerosol fraction, while 23–44% was in the coarse particles. This difference can be explain by difference particles formation mechanisms. The size distribution of hydrocarbon-like aerosol (HOA) shows a distinct ultrafine mode that is commonly associated with fresh emissions while oxygenated organic aerosol (OOA) is generally concentrated in the accumulation mode. These observations suggest that HOA is likely primary aerosol from local, combustion-related emissions and that OOA is secondary organic aerosol (SOA) influenced by regional contributions.The size distribution of hydrocarbon-like aerosol (HOA) shows a distinct ultrafine mode that is commonly associated with fresh emissions while oxygenated organic aerosol (OOA) is generally concentrated in the accumulation mode. These observations suggest that HOA is likely primary aerosol from local, combustion-related emissions and that OOA is secondary organic aerosol (SOA) influenced by regional contributions.