S. Baldy et al., FIELD OBSERVATIONS OF THE VERTICAL-DISTRIBUTION OF TROPOSPHERIC OZONEAT THE ISLAND OF REUNION (SOUTHERN TROPICS), JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 101(D19), 1996, pp. 23835-23849
An analysis of 1 year of tropospheric vertical soundings of ozone at t
he island of Reunion (21 degrees S, 55 degrees E) is presented. High v
alues of ozone concentration are observed in the troposphere above the
inversion level that caps the marine boundary layer (MEL) during the
September to November period, concomitant with active biomass burning
in the southeastern African continent and Madagascar. Tongues (promine
nces of higher values) of enhanced ozone are apparent on vertical prof
iles obtained during this period, and backward trajectories from tongu
e levels are generally traced back to these zones of intense burning.
Profiles of high and almost constant ozone mixing ratio in the whole t
roposphere above the MBL are also obtained during this season and coul
d not be traced back to a definite origin. Conversely, during January
to March, MEL. compounds and humidity are convected in the whole tropo
sphere, and tropospheric ozone is very low. The seasonal variation of
integrated tropospheric ozone is large, up to 30 Dobson units (DU) and
the tropospheric contribution to total columnar ozone could be high,
up to 50-55 DU. This seasonal variation is well correlated with total
ozone mapping spectrometer (TOMS) data, anticorrelated with integrated
water content, and approximately follows, with a small time lag, the
seasonal fire activity in the southeastern Africa, Data from Reunion a
re in accord with equivalent results from Ascension Island (8 degrees
S, 15 degrees W), Brazzaville (Congo; 4 degrees S, 15 degrees E) and N
atal (Brazil; 6 degrees S, 35 degrees W), corroborate satellite observ
ations, and suggest that the concentration of tropospheric ozone in th
e tropics is governed by the coupling of photochemical and dynamical p
rocesses.