Quantification of carbon dioxide, methane, nitrous oxide and chloroform emissions over Ireland from atmospheric observations at Mace Head

Flux estimates of CO₂, CH₄, N₂O and CHC1₃ over Ireland are inferred from continuous atmospheric records of these species. We use radon-222 (²²²Rn) as a reference compound to estimate unknown sources of other species. The correlation between each species and ²²²Rn is calculated for a suite of diurnal events that have been selected in the Mace Head record over the period 1995-1997 to represent air masses exposed to sources over Ireland. We established data selection criteria based on ²²²Rn and ²¹²Pb concentrations. We estimated flux densities of 12 x 10³ kg CH₄ km^-2 yr^-1, 680 kg N₂O km^-2 yr^-1 and 20 kg CHC1₃ km^-2 yr^-1 for CH₄, N₂O and CHC1₃, respectively. We also inferred flux densities of 250 x 10³ kg C km^-2 yr^-1 for CO₂ during wintertime, and of 760 x 10₃ kg C km^-2 yr^-1 for CO₂ during summer night-time. Our CH₄ inferred flux compare well with the CORINAIR90 and CORNAIR94 inventories for Ireland. The N₂O emission flux we inferred is close to the inventory value by CORINAIR90, but twice the inventory value by CORINAIR94 and EDGAR 2.0. This discrepancy may have been caused by the use of the revised 1996 IPCC guidelines for national greenhouse gas inventories in 1994, which include a new methodology for N₂O emissions from agriculture. We carried out the first estimation of CHC1₃ emission fluxes over Ireland. This estimation is 4 times larger than the CHC1₃ emission fluxes measured close to the Mace Head station over peatlands. Our CHC1₃ emission fluxes estimate is consistent with the interpretation of the same data by Ryall (personal communication, 2000), who obtained, using a Lagrangian atmospheric transport model, CHC1₃ fluxes of 24 ± 7 kg CHC1₃ km^-2 yr^-1. Our estimates of CO₂ emission fluxes during summer night-time and wintertime are close to those estimated from inventories and to one biogeochemical model of heterotrophic respiration.