Indirect measurements of the composition of ultrafine particles in the Arctic late-winter
Journal Article
Overview
abstract
; 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; 1.45-1.51, 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 H; 2; SO; 4; and solar; radiation. These particles were highly hygroscopic (HGF=2.1 for 35 nm; 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, while Event 2 spent; more time closer to the surface 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.;
