On the budget of photooxidants in the marine boundary layer of the tropical South Atlantic

Measurements of ozone, hydrogen peroxide, methylhydroperoxide, and formaldehyde in the marine boundary layer of the tropical southern Atlantic Ocean were performed on board the research vessel Polarstern during its cruise from Bremerhaven, Germany (54°N, 8°E), to Punta Arenas, Chile (53°S, 71°W), in October and November 1994. Model calculations were made to estimate the deposition rates of H 2 O 2 and CH 3 OOH. The modeling required that long‐range transport and advection processes of photochemical aged air masses that originated in African biomass burning plumes be taken into account. For H 2 O 2 the dry deposition rate was estimated to be 1 times; 10 −5 /s and the air‐sea flux was estimated to be 4.5 × 10 10 molecules/cm 2 /s, while for CH 3 OOH the dry deposition and the air‐sea flux were estimated to be 0.8 × 10 −5 /s and 3 × 10 10 molecules/cm 2 s, respectively. These values compared well with other estimates. Because of the uncertainties in the rate constants for the photochemical production and loss of methyl hydrogen peroxide the accuracy of the calculated deposition rates for both CH 3 OOH and H 2 O 2 is limited. These chemical rate constants are not accurate enough to provide an unambiguous estimate of the deposition rate constants through simulation of field observations.