Segregation and interpretation of ozone and carbon monoxide measurements by air mass origin at the TOR Station Mace Head, Ireland from 1987 to 1995

Three independent methods have been used to sort the ozone, carbon monoxide, and other radiatively important trace gases measured at Mace Head, Ireland, and thereby distinguish clean air masses transported over the North Atlantic from the more polluted air masses which have recently travelled from the European continent. Over the period April 1987-June 1995 the Northern Hemisphere surface ozone baseline concentrations exhibited a mean concentration of 34.8 ppb, with a small positive trend (+0.19 ppb yr(-1)), while the corresponding trend in air originating from the polluted European areas was negative (-0.39 ppb yr(-1)). Carbon monoxide measurements from March 1990 to December 1994 showed negative trends for both the unpolluted (-0.17 ppb yr(-1)) and polluted data (-13.6 ppb yr(-1)). Overall the continent of Europe was shown to be a small net sink of 2.6 ppb for all occasions when European air was transported to the North Atlantic.