The optical properties and direct radiative forcing potential of atmospheric aerosols in Northeastern Greenland

Abstract The radiative forcing effect of aerosols is an element of climate change that presently carries large uncertainties, especially in the Arctic region. It is particularly important to investigate this due to the severity of observed warming in the Arctic, which is over twice the global rate. This study aims to assess the direct radiative forcing potential of aerosols using measurements of particle number size distribution, optical properties and meteorological data, all of which are common and accessible measurements for Arctic sites. It introduces a measure of the Potential Direct Radiative Forcing (PDRF) which describes the interaction between aerosols and sunlight throughout the year, and is expressed as the irradiance of light scattered or absorbed by aerosols per unit path length that the sunlight travels. PDRF values are calculated for eight different aerosol types, differentiated using k-means clustering of the particle number size distribution spectra observed at Villum Research Station in North Greenland. It also accounts for the intensity of incoming solar radiation, which exhibits extreme seasonality in the Arctic. PDRF was found to peak in the late spring for both the scattering and absorption processes when the Arctic haze is still present in the atmosphere and the daily solar irradiance begins to sharply increase. Interestingly, PDRF was also found to be relatively high in summer, especially from scattering, owing to the intense sunlight. Mean yearly relative contributions to PDRF for scattering from the Biogenic, Anthropogenic, Mixed and Background cluster groups were found to be 20%, 38%, 31% and 11%, respectively. For absorption, the Biogenic, Anthropogenic, Mixed and Background groups contribute 16%, 56%, 19% and 9%, respectively. These results indicate that biogenic aerosols may have a considerable direct radiative impact, which may increase as Arctic sea ice melt results in increased emissions of marine aerosol precursors.