Ambient carbonyls in urban air in Qinzhou were studied form October 2011 to July 2012 to investigate their distribution characteristics and sources. Acetaldehyde (8.04 ± 9.00 µg/m3), formaldehyde (6.70 ± 6.36 µg/m3) and acetone (2.43 ± 2.81 µg/m3) were three most abundant carbonyls, accounting for ~90% of the seven carbonyls identified. Concentrations of most carbonyls showed significantly higher levels in spring and summer than those in autumn and winter. Seasonal and diurnal variations indicated that formaldehyde and acetaldehyde were related to barbecue emissions and photochemical loss, while solvent usage was responsible for acetone. The average C1/C2 ratio was higher (1.92) in summer than that during other seasons (0.52–1.78), implying the positive impact of photochemical loss or formation; and a significantly lower C2/C3 ratio (2.57) was observed in winter than during other seasons (12.47–52.82), suggesting significant emissions from straw burning and barbecues. Formaldehyde and acetaldehyde were the two major contributors (63–97%) to O3 formation, particularly in spring and summer.