Quantifying the impact of natural and anthropogenic aerosol in the Arctic

The Arctic region is currently experiencing an accelerated warming resulting in significant sea-ice loss. The loss of summertime sea-ice will change natural and anthropogenic aerosol emissions in the Arctic which by changes in cloud drop concentrations, atmospheric radiative properties and surface albedo could constitute an important climate feedback. However, our understanding of Arctic aerosol processes is poor, and thus the significant of aerosol feedbacks are uncertain. This thesis uses a global model of aerosol processes (GLOMAP) and surface-level observations to examine the processes controlling Arctic aerosol in the present day and in an environment following sea-ice retreat. The seasonal cycle in Arctic aerosol is typified by large aged particles transported from lower latitudes in the winter and early spring followed by a sharp transition to locally sourced smaller particles in the summer. It is shown that this spring-summer transition is controlled by the shift from inefficient ice-phase cloud scavenging in the early spring to efficient warm-cloud scavenging in the summer. This seasonal cycle is amplified further by the appearance of warm drizzling cloud in the summer which suppress low-level transport into the Arctic boundary layer. Inclusion of stratocumulus and ice-phase scavenging greatly improves the agreement between modelled and observed mass concentrations at six. Arctic and sub-Arctic sites. Likewise, the simulated particle size distribution and cloud condensation nuclei (CCN) number was evaluated against observations. Like aerosol mass, the rapid transition between the late spring and summer size spectra is controlled by the onset of warm scavenging in the Arctic boundary layer. In addition, summertime particle concentrations were shown to originate almost exclusively from nucleation in the Arctic boundary layer, which reproduced the observed size distribution in the central Arctic well. In response to the complete loss of Arctic summer ice, GLOMAP predicts a factor of 10 increase in the source strength of sea spray particles and a factor of 15 increase in the sea-air flux of dimethyl sulfide (DMS). However, the predicted response of CCN is weak, with negative changes (5-10%) over the central Arctic. In the scavenging-dominated Arctic environment, the production of condensable vapour from the oxidation of DMS grows aerosol particles to sizes where they can be scavenged, thereby reducing CCN concentrations in regions with suppressed nucleation. Finally, the Significant increase in shipping emissions in 2050 is shown to have a negligible effect on CCN concentrations, aerosol mass or BC deposition «1 % increase) which is unlikely to be measurable against natural or variability or changes in anthropogenic sources.EThOS - Electronic Theses Online ServiceGBUnited Kingdo