Molecular distributions of dicarboxylic acids, oxocarboxylic acids and α-dicarbonyls in the free troposphere are identified, and their concentration variations between 2014 and 2006 are presented. High nighttime concentrations were probably due to precursor emissions and aqueous-phase oxidation. Biomass burning was significant, but its tracer levoglucosan in 2014 was 5 times lower than 2006 concentrations. Finally, regional emission from anthropogenic activities was identified as a major source.