Concentrations, cumulative exposure and critical levels of ozone in Ireland

Abstract

Concentrations of tropospheric ozone (O3) and exceedance of critical levels to vegetation have been investigated and mapped for Ireland. Hourly ozone concentration data (1995–1997) at 7 seven monitoring stations and the CORINE landcover database, supported by a Geographical Information System, were used. AOT40 (Accumulated exposure Over a Threshold of 40 ppb) was calculated for daylight hours for each station, and mapped using surface interpolation. Average O3 concentrations vary from year to year, and were estimated to be 28 ppb, 26 ppb and 24 ppb for 1995, 1996 and 1997 respectively. Ozone concentrations show a large diurnal variation, with a maximum in the afternoon and a minimum at night-time. The critical level for crops and (semi-)natural vegetation was exceeded in all years examined. The highest exceedance occurred in 1995, where the critical level was exceeded for almost 35% of the mapped area. Approximately 15% and 1% of the mapped area was exposed to exceedance levels during 1996 and 1997 respectively. The maximum cumulative exposures (AOT40) were approximately 5000, 3890 and 3230 ppbh in 1995, 1996 and 1997 respectively. The critical level for forests was not exceeded during the period of investigation