| Summary: | Marine aerosols contribute significantly to global climate directly by absorbing or scattering solar radiation, as well as indirectly by altering the reflectance and persistence of clouds. This work presents results of several investigations into the physicochemical properties of particulate matter over the North East Atlantic ocean. A suite of specifically designed aerosol instrumentation was used to perform an analysis of the characteristics of aerosol size distributions measured in air masses advecting over the Mace Head Atmospheric Research Station during the year 2008. During this time twelve aerosol size distribution clusters were identified as systematically occurring, which were further categorised into four groups with similar characteristics: coastal nucleation category (occurring 21.3 % of the time), open ocean nucleation category (occurring 32.6% of the time), background clean marine category (occurring 26.1% of the time) and anthropogenic category (occurring 20% of the time). Analysis and observations of open ocean new particle production are also reported, where new particle formation events were observed to form a distinct peak in the size distribution with a mode at ~15 nm and grow to a mode of ~50 nm over periods of 24-48 hours, during which time air masses were calculated to have advected over biologically-rich waters in the North Atlantic before detection. A study of size distribution measurements carried out at Mace Head over a seven year period, showed that these nucleation events also exhibit a seasonality, with a monthly average occurrence of 5.7 per percentage occurrence of clean air, peaking in May. In an investigation of new particle formation from Laminaria digitata macroalgae, aerosol nucleation in a range of I2 (0.3 - 76 ppbv) and O3 (<3 - 96 ppbv) mixing ratios was found to be significant, as well as correlated (R2 = 0.95) with I2 for low O3 mixing ratios (<3 ppbv). In experiments where particle production as a function of laboratory-generated I2 over a mixing ratio range of ...
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