Indirect Measurements of the Composition of Ultrafine Particles in the Arctic Late‐Winter

• Published in: Journal of Geophysical Research: Atmospheres
• Main Authors: Myers, Deanna C, Lawler, Michael J, Mauldin, Roy L, Sjostedt, Steven, Dubey, Manvendra, Abbatt, Jonathan, Smith, James N
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: eScholarship, University of California 2021
• Subjects: Climate Action; Life Below Water; OASIS; Utqiagvik; ultrafine aerosol; new particle formation; Atmospheric Sciences; Physical Geography and Environmental Geoscience; Arctic; Arctic Ocean; Sea ice; Alaska
• Online Access: https://escholarship.org/uc/item/7g67410m; https://escholarship.org/content/qt7g67410m/qt7g67410m.pdf; https://doi.org/10.1029/2021jd035428

We present indirect measurements of size-resolved ultrafine particle composition conducted during the Ocean-Atmosphere-Sea Ice-Snowpack (OASIS) Campaign in Utqiagvik, Alaska, during March 2009. This study focuses on measurements of size-resolved particle hygroscopicity and volatility measured over two periods of the campaign. During a period that represents background conditions in this location, particle hygroscopic growth factors (HGF) at 90% relative humidity ranged from 1.45 to 1.51, which combined with volatility measurements suggest a mixture of ∼30% ammoniated sulfates and ∼70% oxidized organics. Two separate regional ultrafine particle growth events were also observed during this campaign. Event 1 coincided with elevated levels of H2SO4 and solar radiation. These particles were highly hygroscopic (HGF=2.1 for 35nm particles), but were almost fully volatilized at 160°C. The air masses associated with both events originated over the Arctic Ocean. Event 1 was influenced by the upper marine boundary layer (200–350m AGL), while Event 2 spent more time closer to the surface (50–150m AGL) and over open ocean leads, suggesting marine influence in growth processes. Event 2 particles were slightly less hygroscopic (HGF=1.94 for 35nm and 1.67 for 15nm particles), and similarly volatile. We hypothesize that particles formed during both events contained 60–70% hygroscopic salts by volume, with the balance for Event 1 being sulfates and oxidized organics for Event 2. These observations suggest that primary sea spray may be an important initiator of ultrafine particle formation events in the Arctic late-winter, but a variety of processes may be responsible for condensational growth.