A study of new particle formation in the marine boundary layer over the central Arctic Ocean using a flexible multicomponent aerosol dynamic model

Abstract

A B S T R A C T Enhancement of number concentrations of particles with sizes less than 25 nm diameter has been frequently observed in the boundary layer over the central Arctic Ocean during summer. The sectional aerosol dynamics model for Marine Aerosol Formation (MAFOR) was applied to evaluate the capability of different nucleation mechanisms to reproduce nucleation events observed during three expeditions (1996, 2001 and 2008) onboard the Swedish icebreaker Oden. Model calculations suggest that a source rate of a condensable organic vapour (OV) of about 2)10 5 cm (3 s (1 is required to reproduce observed growth of nucleation mode particles. Nucleation rates predicted by the newly proposed combined sulphuric acid nucleation mechanism, which best described new particle formation in the Arctic, ranged from 0.04 to 0.1 cm (3 s (1 . This mechanism additively combines ion-mediated nucleation and cluster activation, and treats condensation of OV without correction of the Kelvin effect. In several events, the simultaneous number enhancement of particles in the 20Á50 nm size range remained unexplained by the nucleation mechanisms. This lends support to alternative theories such as the fragmentation of marine gels ( :200Á500 nm diameter in size) by physical or chemical processes.

The summer aerosol in the central Arctic 1991–2008: did it change or not?

“…In hourly data from 2003 to 2010 at the continental reference station Melpitz (Heintzenberg et al, 1998), e.g., a monomodal distribution at the lowest values of N26 (<30 cm −3 ) with a peak at about 110 nm builds up to a broad and much less structured ultrafine region with modes at 42 nm and 17 nm with increasing N26. This is consistent with observations of the concurrent appearance of several distinct particle sizes below 50 nm during typical nucleation events over the pack ice Bigg, 1999, 2010;Karl et al, 2012).…”

“…In several analyzed events, observed in 1996, 2001, and 2008, conventional state-of-the-art nucleation mechanisms (Karl et al, 2012) applied in numerical models could not explain the simultaneous number enhancement of particles in the 20-50 nm diameter size range. The analyzed cases covered the central Arctic, the marginal ice zone and open waters.…”

“…Lannefors et al, 1983;Bigg et al, 1996;Covert et al, 1996, and Table 2). A common feature of all events with enhanced levels of 3-5 nm particles is that the simultaneous increases in particle number also occurred in other distinct size ranges <50 nm diameter showing relatively high concentrations (up to 500 cm −3 ) for a few hours (Leck and Bigg, 1999;Leck and Bigg, 2010;Karl et al, 2012). At sizes >10 nm number concentrations increase with size up to a maximum that lies between 20 and 60 nm (Kerminen and Leck, 2001;Leck and Bigg, 2005b; and Section 6 of this study) a smaller range compared with other marine locations where the maximum lies in the range 20 to 100 nm diameter (Heintzenberg et al, 2004).…”

“…In the summer Arctic concentrations of particles <10 nm are usually very low, but on frequent occasions, relative to lower latitudes, concentrations may suddenly increase dramatically for 5-12 hours with hardly any detected subsequent growth, before particles are scavenged by fog or precipitation (Karl et al, 2012). During the nucleation events high concentrations Table 2.…”

Simplified mechanism for new particle formation from methanesulfonic acid, amines, and water via experiments and ab initio calculations

“…Several field studies have shown enhanced MSA concentrations in small particles when ammonia or amines are present (37,38), supporting a role for MSA and amines in new particle formation. The impact of MSA and amines on new particle formation may be especially important in the remote marine atmosphere, particularly in polar regions (39)(40)(41). However, mechanisms of particle formation in such areas remain unclear.…”