ight Aerosol Mass Spectrometry The chemical composition, concentration, size, and possible sources of atmospheric particles at remote Baengnyeong Island, South Korea were explored using high-resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS). Situated in the Yellow Sea off the West coast of N. Korea, this site is well placed to investigate atmospheric chemistry and transport involving air masses from a number of Asian sources. Sulfate was the dominant aerosol component (concentrations averaged 6.53 µg/m3 and ranged to 34.49 µg/m3), followed by total organics (avg. = 3.36 µg/m3; max. = 12.64 µg/m3); organic nitrogen (avg. = 2.47 µg/m3; max. = 12.32 µg/m3) and organosulfur compounds were present. Nitrate (avg. = 0.76 µg/m3; max. = 8.96 µg/m3) and ammonium concentrations (avg. = 1.33 µg/m3; max. = 8.47 µg/m3) were low. Meteorological back-trajectories indicated particle transport from China and mainland Korea; particle size distributions for chemical components during transport events from China showed different sizes for organics and nitrate than for sulfate, signifying externally mixed particles (Lee et al., in preparation); this is corroborated by episodes of increased nitrate and organics without corresponding increases in other species. Statistical technique Positive Matrix Factorization yielded two types of organic aerosol dominated by Low-Volatility Oxidized Organic Aerosol (LV-OOA), whose highly oxidized nature supports other indications of long-range particle transport. Semi-Volatile Oxidized Organic Aerosol (SV-OOA) is somewhat oxidized, indicating shorter transport distance or ageing time. Significant diurnal concentration variations are not observed, which may be explained by the lack of local particulate sources and stable boundary layer thickness over the sea. Lastly, a Potential Aerosol Mass experiment was performed in which ambient aerosol was rapidly oxidized in a chamber; this can explore the types of chemical reactions oxidizing the organic aerosol and the potential of an air mass to form more particle mass as it ages (Kang et al., 2007), with attendant health and environmental effects. Two distinct chemistries were observed at Baengnyeong. In the first, mass increased during PAM oxidation for all chemical components; this may indicate oxidation reactions such as oligomerization and functionalization, which decrease the vapor pressure of molecules and drive them into the particulate phase. During the second period, organic mass was lost during PAM oxidation, while mass of sulfate and other species increased. This may be explained by fragmentation oxidation reactions, which break organic molecules into smaller molecules; the commensurate increase in vapor pressure leads to molecule volatilization and a decrease in particle mass. Kang, E., Root, M. J., Toohey, D. W., and Brune, W. H. (2007). "Introducing the concept of Potential AerosolMass (PAM)." Atmos. Chem. Phys. 7:5727–5744, doi:10.5194/acp-7-5727-2007. Paatero, P. and U. Tapper (1994). "Positive matrix factorization: A non-negative factor model with optimal utilization of error estimates of data values." Environmetrics 5(2): 111-126.