Mixing ratios of acetic (CH3COOH), formic (HCOOH), pyruvic (CH3COCOOH), and
oxalic ((COOH)(2)) acids were measured both in gas and particulate phase i
n the marine boundary layer, over the Atlantic Ocean from 63 degrees N to 3
9 degrees S on board of the RN Polarstern in October/November 1996, The ave
rage mixing ratios for gas phase CH,COOH, HCOOH, CH3COCOOH, and (COOH)(2) w
ere 291.2 +/- 151.9, 448.7 +/- 182.1, 1.1 +/- 1.0, and 6.1 +/- 5.4 parts pe
r trillion by volume (pptv), respective ly. The partitioning of these acids
in the aerosol phase and the size distribution of their particulate form w
as also investigated. In the fine mode the mean mixing ratios for acetate,
formate, pyruvate, and oxalate were 69.7 +/- 47.5, 32.5 +/- 39.4, 1.0 +/- 1
.0, and 5.1 +/- 3.7 pptv, respectively. Elevated levels of all organic acid
s were encountered in the southern hemisphere (springtime) compared to the
northern hemisphere (autumn), indicating a possible seasonal variation in t
heir source strength and/or enhanced photochemical production. The observed
distributions of formic and acetic acids have been compared to the results
of a global chemistry/transport three-dimensional model. The model results
show that acetic acid has mainly secondary photochemical sources (about 12
0 Tg CH3COOH/yr). On the opposite, the known chemical sources of HCOOH are
quite weak (20 Tg HCOOH/yr) and insufficient to simulate the HCOOH levels o
bserved in the marine atmosphere. A local marine source of HCOOH of about 5
0 Tg/yr on a global scale is required to reasonably simulate the observatio
ns in the marine atmosphere.