Characterizing the contribution of summer aerosol to cloud formation in the Canadian Arctic

Arctic aerosols undergo a strong seasonal cycle, with higher aerosol mass in the winter and spring from pollution transported from southerly latitudes, and much lower aerosol mass in the summer when wet deposition removes these aerosols from the atmosphere before they can reach the Arctic. The radiation budget in the summer is extremely important since it contributes to surface warming, so the effect of aerosols on cloud properties in summer must be characterized. The clean periods in the summer can affect radiation in two ways: they can lead to new particle formation (NPF) events, followed by particle growth that allow the particles to become active as cloud condensation nuclei (CCN) at moderate supersaturations (<0.3%); and they can lead to CCN-limited periods, when not enough aerosol particles are present to allow clouds to form. This study characterizes the frequency of occurrence of these two regimes to better understand the contributions of aerosols on clouds, and ultimately radiation, in the Canadian Arctic. To accomplish this, aerosol size distributions measured by a scanning mobility particle sizer (10 – 500 nm) were analyzed from the Polar Environment Atmospheric Research Laboratory (PEARL) at Eureka, Nunavut on Ellesmere Island (80N, 86.5W) in the Canadian Arctic Archipelago from 2015 – 2023. Monthly frequency occurrence of days classified as NPF and CCN-limited will be presented, as well as related meteorological conditions (e.g. temperature, relative humidity, boundary layer height). These findings provide an understanding of the importance of these two unique aerosol regimes in the Arctic summer and their potential impact on clouds and radiation.