OZONE AND CARBON-MONOXIDE MEASUREMENTS AT A REMOTE MARITIME LOCATION, MACE-HEAD, IRELAND, FROM 1990 TO 1992

Despite the importance of carbon monoxide in controlling the oxidising capacity of the troposphere and as a precursor to ground level ozone in regional scale photochemical episodes, few measurements are available for northwest Europe. Hourly carbon monoxide and ozone measurements are reported here for the Mace Head site on the Atlantic coast of the Republic of Ireland, for the three-year period from 1990 to 1992. Evidence is found for the advection of air masses containing elevated concentrations of carbon monoxide, from the continent of Europe to the Mace Head site, particularly when the wind flow is easterly and southeasterly. Using the simultaneous measurements of man-made halocarbons and daily wind sector allocations, it has been possible to identify the Northern Hemisphere baseline carbon monoxide concentration at 53 degrees N of 128 +/- 4 ppb and show that there has been a significant trend to increasing concentrations over the three-year period amounting to about 0.8 ppb yr(-1). The European source strength for carbon monoxide has been quantified as 128 kg/head of population/yr, in excellent agreement with literature emission inventories. A downward trend in European CO emissions of about 13% yr(-1) has been detected, presumably reflecting the steady reduction due to motor vehicle emission regulations. Over the period from March 1987 to December 1992 the continent of Europe has been shown to be a small, net ozone sink of 2.6-2.8 ppb over all of those occasions when European air flowed out over the Atlantic Ocean over Mace Head, A box model analysis of the observed simultaneous summertime carbon monoxide and ozone concentration variations points to between 1.7 and 7 ozone molecules being produced per NOx molecule oxidised.