Marine nanogels as a source of atmospheric nanoparticles in the high Arctic

Abstract

The high Arctic (north of 80°N) in summer is a region characterized by clean air and low abundances of preexisting particles. Marine colloidal nanogels i.e., assembled dissolved organic carbohydrate polymer networks have recently been confirmed to be present in both airborne particles and cloud water over the Arctic pack ice area. A novel route to atmospheric nanoparticles that appears to be operative in the high Arctic is suggested. It involves the injection of marine granular nanogels into the air from evaporating fog and cloud droplets, and is supported by observational and theoretical evidence obtained from a case study. Statistical analysis of the aerosol size distribution data recorded in the years 1991, 1996, 2001, and 2008 classified 75 nanoparticle events—covering 17% of the observed time period—as nanogel‐type events, characterized by the spontaneous appearance of several distinct size bands below 200 nm diameter.

Vertical profiling of aerosol particles and trace gases over the central Arctic Ocean during summer

“…The combination of particle release from droplets together with classical nucleation and growth involving H 2 SO 4 and organic vapours is thus suggested to have been responsible for the NPF event. Indeed, a modelling study carried out by Karl et al (2013) shows good agreement with observed number concentrations, when both nucleation and growth of condensable vapours as well as emissions of marine nanogels are simulated. Most likely, the relative contribution of nucleation and growth by H 2 SO 4 and condensable organic vapours to the observed increase in concentrations in the sub-10 nm size range became greater several hours later, during the early hours of 2 September, when the origin of the incoming air mass shifted to the Beaufort Sea.…”

“…Via a process involving dissipation of fog/cloud droplets and release and break-up of particles contained within the cloud droplets Bigg, 1999, 2010), the open lead source is suggested to be responsible for the episodic occurrences, such as that during period 3, on 29 August and at ground level during period 4, in the evening on 1 September. However, nucleation and early growth by condensable vapours, such as H 2 SO 4 and organics, are also likely to contribute to the observed NPF event, with a combination of marine gel emissions and nucleation best explaining the observations according to a modeling study (Karl et al, 2013).…”

“…In addition, it was shown that the availability of condensable vapours is limited in the PBL over the inner Arctic, and that the concentration of DMS, a precursor to H 2 SO 4 , is often not sufficient to sustain growth into the super 10 nm diameter size range (Karl et al, 2013), leaving the observed coappearance of particles in the 20-50 nm diameter size range coinciding with nucleation unexplained in many cases. Also during this NPF event during period 4, the concentrations of precursor gases measured by the PTR-TOF on board Oden were very low (DMS concentrations were below the detection limit of 4 ppt(v) (30 min integration)), preventing the Kelvin barrier from being overcome, and thus excluding further possible growth of nanometre-sized clusters.…”

“…Again the simultaneous increases in concentration occurring in both the D 3−14 and D 14−300 size ranges suggest that a different mechanism may have been involved. In an attempt to explain the characteristics of the new particle formation events in the high Arctic, a hypothesis has been put forward linking the NPF events to evaporation of low-level cloud or fog droplets brought about by mixing of the droplets with dry air at the top and edges of a cloud/fog (Leck and Bigg, 2010;Karl et al, 2013), whereby particle breakup could take place during evaporation.The fragmentation of particles released from the evaporating cloud droplets could result in release of both ultrafine particles and Aitken-mode particles (Leck and Bigg, 2010). Based on the visibility and ceilometer measurements located on board Oden, rapid evaporation of low cloud/fog droplets was observed approximately 36 min before the start of the new particle formation event seen by the TDMPS.…”

Size-resolved atmospheric particulate polysaccharides in the high summer Arctic

“…In an attempt to explain the characteristics of "colloidal fragmentation" of polymer gels in the high Arctic, a hypothesis has been put forward linking it to evaporation of cloudor fog -droplets by mixing with air, low in moister, at the top and edges of a cloud/fog (Karl et al, 2013;Bigg, 1999, 2010), whereby the colloidal fragments would be released during evaporation.…”