Evidence for marine biogenic influence on summertime Arctic aerosol

Abstract

Abstract We present vertically resolved observations of aerosol composition during pristine summertime Arctic background conditions. The methansulfonic acid (MSA)‐to‐sulfate ratio peaked near the surface (mean 0.10), indicating a contribution from ocean‐derived biogenic sulfur. Similarly, the organic aerosol (OA)‐to‐sulfate ratio increased toward the surface (mean 2.0). Both MSA‐to‐sulfate and OA‐to‐sulfate ratios were significantly correlated with FLEXPART‐WRF‐predicted air mass residence time over open water, indicating marine‐influenced OA. External mixing of sea salt aerosol from a larger number fraction of organic, sulfate, and amine‐containing particles, together with low wind speeds (median 4.7 m s −1 ), suggests a role for secondary organic aerosol formation. Cloud condensation nuclei concentrations were nearly constant (∼120 cm −3 ) when the OA fraction was <60% and increased to 350 cm −3 when the organic fraction was larger and residence times over open water were longer. Our observations illustrate the importance of marine‐influenced OA under Arctic background conditions, which are likely to change as the Arctic transitions to larger areas of open water.