Seasonality in size segregated biogenic, anthropogenic and sea salt sulfate aerosols over the North Atlantic

Size segregated aerosol sulfate concentration was measured over a south to north transect of the North Atlantic, extending from 37° N to the base of Greenland, during spring, summer and fall of 2003. Sea salt sulfate for all three seasons was found in large diameter aerosols (>0.95 μm), but spring season sea salt was also persistently found in the finest aerosols collected (<0.49 μm). Non sea salt sulfate concentrations in the 0.49–0.95 μm range (large accumulation mode) were elevated in summer (5.7 ± 7.0 nmol m−3) relative to spring (1.4 ± 0.7 nmol m−3) and fall (1.3 ± 1.0 nmol m−3). Non sea salt sulfate was apportioned into biogenic and anthropogenic sulfate using sulfur isotopes. Little to no biogenic sulfate was observed in the spring. However, in the summer and fall biogenic sulfate concentration averaged 2.3 ± 1.4 nmol m−3 and 2.0 ± 2.2 nmol m−3 respectively in aerosols less than 0.49 μm diameter corresponding to approximately 40% of the non sea salt sulfate load for both seasons. Anthropogenic sulfate was detectable throughout the study with the largest concentrations of fine aerosol anthropogenic sulfate (up to 76 nmol m−3) observed in samples collected at lower latitudes. isotopes were used to determine aerosol growth from local SO2 oxidation in the summer. SO2 oxidation is calculated to be significant in two aerosol growth events. These samples had the largest biogenic sulfate concentrations in the 0.49–0.95 μm range aerosols and showed high concentrations of sulfate in the 0.49–0.95 μm relative to the <0.49 μm diameter aerosols. Sulfate from local SO2 oxidation was calculated to be approximately 40% of the non sea salt sulfate present in these two events.