Seasonal characteristics of submicrometer organic aerosols in urban Gwangju, Korea using an aerosol mass spectrometer

Chemical characterization of organic aerosol (OA) was conducted using an aerosol mass spectrometer (AMS) in urban Gwangju, Korea, during the fall (8/30/2011–9/19/2011), winter (12/19/2011–12/30/2011), spring (5/15/2012–5/24/2012), and summer (7/23/2012–8/6/2012). OA was found to be the most dominant component of non-refractory submicrometer particles, with an average concentration of 4.39 μg m−3. The oxygenated organic aerosol (OOA) content was higher than the hydrocarbon-like organic aerosol (HOA) content (68.1% versus 31.9%), and the less volatile-OOA (LV-OOA) content was higher than the semi-volatile OOA (SV-OOA) content (57.0% versus 43.0%). The seasonal data showed that both HOA and LV-OOA were abundant in winter due to the enhancement of the local OA source strength under strong temperature inversion and the frequent long-range transportation of aged air masses from polluted areas. The OA more than doubled when a northwest air mass occurred compared to the other air masses in winter, suggesting that the long-range transported organic species constitute more than 50% of the OA. Changes in the mixing height (i.e., dilution) and the strength of the HOA sources led to a pronounced diurnal pattern for the HOA in winter. A clear transition for the OA components was observed from winter to summer. In summer, LV-OOA became the most dominant component and increased in the afternoon in contrast to the HOA and SV-OOA. A bimodal size distribution of the OA was observed in all seasons due to multiple OA sources and aging. Optical properties of PM2.5 measured in the spring showed that the single scattering albedo (SSA) at 532 nm increased in the afternoon along with the LV-OOA. The HOA was better correlated with the light absorption coefficient than the light scattering coefficient, suggesting that the HOA included a significant amount of light absorbing organics and/or were produced at the same time as the light absorbing black carbon.