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. When computing climatological averages of atmospheric trace-gas mixing ratiosobtained from satellite-based measurements, sampling biases arise if datacoverage is not uniform in space and time. Homogeneous spatiotemporalcoverage is essentially impossible to achieve. Solar occultationmeasurements, by virtue of satellite orbit and the requirement of directobservation of the sun through the atmosphere, result in particularly sparsespatial coverage. In this proof-of-concept study, a method is presented toadjust for such sampling biases when calculating climatological means. Themethod is demonstrated using carbonyl sulfide (OCS) measurements at 16 kmaltitude from the ACE-FTS (Atmospheric Chemistry Experiment Fourier TransformSpectrometer). At this altitude, OCS mixing ratios show a steep gradientbetween the poles and Equator. ACE-FTS measurements, which are provided asvertically resolved profiles, and integrated stratospheric OCS columns areused in this study. The bias adjustment procedure requires no additionalinformation other than the satellite data product itself. In particular, themethod does not rely on atmospheric models with potentially unreliabletransport or chemistry parameterizations, and the results can be useduncompromised to test and validate such models. It is expected to begenerally applicable when constructing climatologies of long-lived tracersfrom sparsely and heterogeneously sampled satellite measurements. In thefirst step of the adjustment procedure, a regression model is used to fit a2-D surface to all available ACE-FTS OCS measurements as a function ofday-of-year and latitude. The regression model fit is used to calculate anadjustment factor that is then used to adjust each measurement individually.The mean of the adjusted measurement points of a chosen latitude range andseason is then used as the bias-free climatological value. When applying theadjustment factor to seasonal averages in 30 ∘ zones, the maximumspatiotemporal sampling bias adjustment was 11 % for OCS mixing ratios at16 km and 5 % for the stratospheric OCS column. The adjustments werevalidated against the much denser and more homogeneous OCS data product fromthe limb-sounding MIPAS (Michelson Interferometer for Passive AtmosphericSounding) instrument, and both the direction and magnitude of the adjustments were in agreement with the adjustment ofthe ACE-FTS data.

Sampling bias adjustment for sparsely sampled satellite measurements applied to ACE-FTS carbonyl sulfide observations