Dissolved organic carbon and organic acids in coastal New Zealand rainwater

Dissolved organic carbon (DOC), formate, acetate, oxalate and a variety of inorganic ions were measured in 54 rain events collected on the southern portion of the South Island of New Zealand. Concentrations of DOC ranged from a low of 10 μM to a high of 401 μM with a volume weighted average concentration of 58 μM which is in the range of concentrations measured at coastal locations in the Northern Hemisphere. The concentration of DOC varied by season with warm season rain (October–March) having somewhat higher concentrations relative to winter rain events (April–September). DOC levels in rain were also influenced by storm origin with maritime events having significantly lower levels relative to terrestrially influenced storms. Formic and acetic acids comprised a relatively small fraction of the DOC pool in New Zealand rain with volume weighted average concentrations of 1.5 μM which was not influenced by storm origin or season. There was a significant correlation between formic and acetic acid concentrations in these rain events suggesting they have similar sources or have different sources of approximately the same strength. This DOC and organic acids data will allow for a better understanding of the global tropospheric transport of carbon compounds and will aid in quantification of atmospheric carbon removal via wet deposition in the Southern Hemisphere.