[1] Initiated in 1997, the year-round study of formic and acetic acids was maintained until 2011 at the coastal Antarctic site of Dumont d'Urville. The records show that formic and acetic acids are rather abundant in summer with typical mixing ratios of 200 pptv and 700 pptv, respectively. With the aim to constrain their budget, investigations of their potential marine precursors like short-chain alkenes and acetaldehyde were initiated in 2011. Acetic acid levels in December 2010 were four times higher than those observed over summers back to 1997. These unusually high levels were accompanied by unusually high levels of ammonia, and by an enrichment of oxalate in aerosols. These observations suggest that the guano decomposition in the large penguin colonies present at the site was particularly strong under weather conditions encountered in spring 2010 (important snow storms followed by sunny days with mild temperatures). Although being dependent on environmental conditions, this process greatly impacts the local atmospheric budget of acetic acid, acetaldehyde, and acetone during the entire summer season. Present at levels as high as 500 pptv, acetaldehyde may represent the major precursor of acetic acid, alkene-ozone reactions remaining insignificant sources. Far less influenced by penguin emissions, the budget of formic acid remains not fully understood even if alkene-ozone reactions contribute significantly.

HCHO was monitored throughout the year 2009 at the coastal East Antarctic site of Dumont d'Urville (DDU) using Aerolaser AL‐4021 analyzers. The accurate determination of less than 100 pptv required optimization of the analyzers, in particular, to minimize effects of changing ambient temperatures. The impact of station activities and of the presence of large penguin colonies at the site in summer was scrutinized. The obtained contamination‐free record indicates monthly means close to 50 pptv from May to September and a maximum of 200 pptv in January. Zero‐dimensional and 2‐D calculations suggest that in summer, the largest HCHO source is the gas‐phase photochemistry (80%) mainly driven by methane oxidation, which is considerably greater than from snow emissions (20%). The influence of light alkenes, dimethyl sulfide, and halogens remains weak. In winter, snow emissions represent the main HCHO source (70%). These findings are compared to previous studies conducted at the West Antarctic coast. It is shown that in summer the HCHO production from methane chemistry is 3 times more efficient at DDU than at the west coast due to more frequent arrival of oxidant‐rich air masses from inland Antarctica. Halogen chemistry is found to represent a weak HCHO sink at both West and East Antarctica. Compared to DDU, the shallower atmospheric boundary layer and the less efficient gas‐phase production at the west coast make the snow pack the dominant HCHO source (85%) compared to gas‐phase photochemistry (15%) there in summer.