Arctic Sea Spray Aerosol Production during Polar Night

Delayed fall sea ice freeze-up in the Alaskan Arctic is dramatically changing the region in the fall-winter. However, due to logistical challenges, aerosol composition measurements have been scarce during the fall-winter transition (following polar sunset and into polar night) in Arctic. This lack of observations hinders our understanding of aerosol-cloud-climate interactions in this season. Here we report the first real-time aerosol chemical composition measurements near Utqiaġvik (Barrow), Alaska, during Polar Night. Real-time individual mass spectra of single particles were collected by an aerosol time-of-flight mass spectrometer (ATOFMS) from November 9 to December 18, 2018. The Beaufort Sea is located 6 km to the north of the measurement site, and the coastline gradually froze up over the 40-day field campaign with sea ice coverage changing from nearly none to almost fully covered by sea ice, with open leads often present. Sea spray aerosol (SSA) accounted for ~30% of the over 0.5 million individual particles chemically analyzed in the study. SSA dominated the supermicron (>1 μm) particles and also comprised a significant fraction of submicron particles (0.07-1 μm). The presence of fresh, non-chloride-depleted SSA particles were correlated with the wind speed, consistent with observed local wave-breaking. Aged SSA particles were chloride-depleted and nitrate- and sulfate-enriched, and the presence of these particles did not depend on wind speed, indicating longer atmospheric age and long-distance transport. This study showed that coastal SSA production to continue to be an important local Arctic source even through Polar Night. Due to its large size and hygroscopicity, SSA is likely the most important contributor to available cloud condensation nuclei and contribute to cloud formation during Polar Night.