The Arctic region is witnessing changes on an unprecedented level. Surface air temperatures have increased at a rate four times the global average. Two of the main climate forcers that are responsible for perturbing the radiative balance in the Arctic are greenhouse gases and atmospheric aerosols. Aerosols are tiny solid or liquid particles suspended in the atmosphere that range in size from a few nanometres to tens of microns.  These particles affect the climate by interacting with radiation and influencing cloud formation, brightness, and longevity.  The work presented in this thesis aims to improve our understanding of the drivers and mechanisms involved in controlling both the seasonal variations and the long-term changes in Arctic aerosols, and analyse the general aerosol lifecycle.  In a changing Arctic, both the emissions of anthropogenic and natural aerosol particles have and are expected to continue to change. For one, the long-range transport of anthropogenic aerosols is likely to continue to decline with reductions in emissions.

Measurements of Arctic aerosols were carried out at a research observatory on Svalbard. In this thesis, a variety of instrumentation and measurements were used to assess seasonal and long-term changes in various aerosol-related variables.  The work in this thesis shows that the concentration of light-absorbing aerosol particles has decreased significantly over the past two decades, with the largest decrease in contributions from northern Siberia.  This thesis argues that a quarter of the overall reduction is due to changes to the removal processes via wet scavenging. In this thesis, the changes in environmental parameters along the transport pathway to the site are explored. From this perspective, precipitation is shown to act as both a source and a sink, impacting the number of particles depending on their size, whilst solar radiation is shown to promote an increase in the number of aerosol particles over the entire size spectrum.  Furthermore, using the first long-term time series measuring light-absorbing particles inside and outside of clouds, the process of nucleation scavenging is explored. Increased uptake of light-absorbing particles into cloud droplets is presented from April until October. Incorporation of these particles into cloud droplets is shown to be dependent on temperature and cloud water content. Lastly, the frequency in the production of small particles, barely a nanometre in diameter, in the vicinity of Svalbard is shown to be heavily influenced by solar radiation and the total surface area of pre-existing aerosol particles.  The Greenland Sea is shown to be a relatively larger source of these small particles compared to neighbouring seas.  Its shown that the total surface area of pre-existing aerosols within airmasses is reduced through cloud and precipitation events, setting the stage for new particle formation and the replenishment of aerosol particles in the presence of solar radiation. 

Understanding how these findings can be broadened and applied across a larger geographical region remains to be answered. Additionally, the overall effect these mechanisms and changes can have on the radiative balance in the Arctic requires further exploration.