ASSESSMENT OF TROPICAL OH SEASONALITY USING ATMOSPHERIC (CO)-C-14 MEASUREMENTS FROM BARBADOS

(CO)-C-14 can be used to assess the mean OH concentration if the atmos pheric inventory is determined. However, atmospheric transport must be well represented. The dependence on transport has previously been pre dicted in model studies to be much smaller in the tropics than in the middle latitudes. To test this, we made weekly measurements of (CO)-C- 14 from a tropical station in the Atlantic (Barbados, West Indies, 13 degrees 10'N, 53 degrees 26'W) from July 1996 to July 1997. These data are compared with the (CO)-C-14 seasonal cycle predicted from a zero dimensional chemistry model. Results show that the observed seasonal c ycle correlates well with predicted (CO)-C-14 from the chemistry model during the summer and fall, however significant deviation from the ch emistry model becomes apparent in the wintertime, which is probably la rgely a result of (CO)-C-14 being transported to the tropics from the middle latitudes, and is in contrast to earlier modeling studies. Tran sport has a stronger effect in the winter months because the latitudin al gradient in (CO)-C-14 is large and the lifetime is long, since OH c oncentrations are at their seasonal low.