Atmospheric submicron particles were collected on Teflon filters downstream of a three-stage concentrator aboard the National Center for Atmospheric Research C-130 aircraft near Japan during the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia). Particle-phase organic carbon (OC) was quantified using Fourier transform infrared (FTIR) transmission spectroscopy. Silicate, carbonate, alkane, alkene, aromatic, alcohol, carbonyl, amine, and organosulfate functional groups were identified and separated with a four-solvent rinsing procedure. X-ray fluorescence identified elemental composition. Total OC constructed from FTIR measurements agreed with simultaneous thermal-optical OC measurements with a slope of 0.91 and an R2 value of 0.93. OC varied from 0.4 to 14.2 μg m−3, and organic mass varied from 0.6 to 19.6 μg m−3, representing on average 36% of the identified submicron aerosol mass. Measured carbon monoxide (CO) to OC slopes illustrate 10 groups of air from regions described by an Asian emissions inventory. The CO/OC slope is used to compare sources and their influence on organic composition. Fifty-two percent of ACE-Asia samples have CO/OC slopes indicative of biomass combustion. Unitless CO/OC slopes above 15 are associated with increased fractions of alcohol groups, unsaturated C-H groups, and inorganic nitrate. Increased carbonyl carbon fractions in air originating over northern Asia are consistent with secondary OC formation. Case studies in the boundary layer demonstrate that aerosol compositions downwind of large Asian aerosol sources show clear regional composition signatures.