To bridge the gaps in modeling and observational results due to insufficient understanding of aerosol properties, co-located measurements of aerosols and trace gases were conducted at SGP during the HI-SCALE campaign. Organic aerosols at the SGP site exhibited to be highly oxidized, and biogenic emissions appear to largely control the formation of organic aerosols. Seasonal variations of sources and meteorological impacts likely resulted in the highly oxygenated feature of aerosols.