  Here we report a modelling study of the spring ozone maximum and its
interhemispheric asymmetry in the remote marine boundary layer (MBL). The
modelled results are examined at the surface and on a series of time-height
cross sections at several locations spread over the Atlantic, the Indian, and
the Pacific Oceans. Comparison of model with surface measurements at remote MBL
stations indicate a close agreement. The most striking feature of the
hemispheric spring ozone maximum in the MBL can be most easily identified at
the NH sites of Westman Island, Bermuda, and Mauna Loa, and at the SH site of
Samoa. Modelled ozone vertical distributions in the troposphere are compared
with ozone profiles. For the Atlantic and the Indian sites, the model generally
produces a hemispheric spring ozone maximum close to those of the measurements.
The model also produces a spring ozone maximum in the northeastern and tropical
north Pacific close to those measurements, and at sites in the NH high
latitudes. The good agreement between model and measurements indicate that the
model can reproduce the proposed mechanisms responsible for producing the
spring ozone maximum in these regions of the MBL, lending confidence in the use
of the model to investigate MBL ozone chemistry (see part 2 and part 3). The
spring ozone maximum in the tropical central south Pacific and eastern
equatorial Pacific are less well reproduced by the model, indicating that both
the transport of $O_3$ precursors from biomass burning emissions taking place
in southeastern Asia, Australia, Oceania, southern Africa, and South America
are not well represented in the model in these regions. Overall, the model
produces a better simulation at sites where the stratosphere and biomass
burning emissions are the major contributors.
