An analyser's calibration data is not affected by height differences between where it was calibrated (e.g. in the UK) and where it is used (e.g. 600 metres above sea level, in a city like Madrid).

There is no effect from changes in atmospheric pressure on electrochemical sensors as they operate on a volume per volume basis - a part per million is a part per million at any height. The only pressure effect on sensors is caused by pressure pulses/transients or back pressure from the exhaust.