Aerosol light absorption in the North Atlantic: trends and seasonal characteristics during the period 1989 to 2003

The frequency of occurrence of the hourly averaged aerosol absorption datais found to be bimodally distributed. The two modes result from clean marineair and anthropogenically polluted continental air both being advected tothe station dependent on the prevailing wind direction. The hourly averagesof the marine portion of the aerosol light absorption are found to followclosely a lognormal distribution with a geometric mean of0.310 Mm-1. The hourly averages of continental sector aerosolabsorption are neither normally nor lognormally distributed and have anarithmetic mean of 6.36 Mm-1, indicating the presence ofanthropogenic sources for BC east of the Mace Head station.

The time series of the monthly averaged attenuation coefficient σ_att ofboth marine and continental sector aerosol shows an increase from 1989 to1997 and a levelling off thereafter.

The monthly maximum of marine sector σ_att is found in May. Trend andseasonal characteristics of the clean marine aerosol attenuationcoefficients observed at Mace Head appear to be driven by meteorologicalfactors, as indicated by rainfall data and by trends in the North AtlanticOscillation (NAO) indices. The observed increasing trends of the continentalsector σ_att from 1989 up to 1997 are possibly related to changes in BCemissions over Ireland, calculated from UNSTAT (2002) fuel consumption data. 展开▼