Long-term INP measurements from four stations across the globe

Abstract

Abstract. Ice particle activation and evolution have important atmospheric implications for cloud formation, initiation of precipitation and radiative interactions. In many cases the initial formation of atmospheric ice requires the presence of a nucleating seed, an ice nucleating particle (INP), to facilitate its first emergence. Unfortunately, few long-term measurements of INPs exist and as a result, knowledge about geographic and seasonal variations of INP concentrations is sparse. Here we present data from nearly two years of INP measurements from four stations in different regions of the world: the Amazon, the Caribbean, Central Europe and the Norwegian Arctic. The sites feature diverse geographical climates and ecosystems that are associated with dissimilar transport patterns, aerosol characteristics and levels of anthropogenic impact (ranging from near pristine to mostly rural). Interestingly, observed INP concentrations do not differ greatly from site to site, but usually fall well within the same order of magnitude. Moreover, short-term variability overwhelms all long-term trends and/or seasonality in the INP concentration at all locations. An analysis of the frequency distributions of INP concentrations suggests that INPs tend to be well-mixed and reflective of large-scale air mass movements. No universal physical or chemical parameter could be identified to be a causal link driving INP climatology, highlighting the complex nature of the ice nucleation process. Amazonian INP concentrations were mostly unaffected by the biomass burning season, even though aerosol concentrations increase by a factor of 10 from the wet to dry season. Caribbean INPs were positively correlated to parameters related to transported mineral dust, which is known to increase during the northern hemispheric summer. A wind sector analysis revealed the absence of an anthropogenic impact on average INP concentrations at the Central European site. Likewise, no Arctic Haze influence was observed on INPs at the Norwegian site, where low concentrations were generally measured. We consider the collected data to be a unique resource for the community that illustrates some of the challenges and knowledge gaps of the field in general, while specifically highlighting the need for more long-term observations of INPs worldwide.

The seasonal cycle of ice-nucleating particles linked to the abundance of biogenic aerosol in boreal forests

“…However, that observation may not represent the full picture of INP in those locations. The short sampling times (low volumes; 1 h per day) and/or colder activation temperatures may serve to maximize sampling variability and mask any potential biological signal (Schrod et al 2020). To date, these studies present the first observations and indications of the seasonal variability of INP concentrations, addressing the need for more long-term INP observations.…”

“…The authors suggest these maxima are related to a Saharan dust event and a cold front passage. Schrod et al (2020) describe a global network of four INP sampling stations, at a range of Northern Hemisphere latitudes, where atmospheric aerosol samples were collected on substrates for 2 years from September 2014. The substrates were analysed for deposition and condensation mode INPs using the FRIDGE (FRankfurt Ice nucleation Deposition freezinG Experiment) isothermal static diffusion chamber (Schrod et al, 2020).…”

“…Schrod et al (2020) describe a global network of four INP sampling stations, at a range of Northern Hemisphere latitudes, where atmospheric aerosol samples were collected on substrates for 2 years from September 2014. The substrates were analysed for deposition and condensation mode INPs using the FRIDGE (FRankfurt Ice nucleation Deposition freezinG Experiment) isothermal static diffusion chamber (Schrod et al, 2020). The Schrod et al (2020) results do not yield a clear seasonality but instead show that short-term variability overwhelms long-term trends.…”

“…The substrates were analysed for deposition and condensation mode INPs using the FRIDGE (FRankfurt Ice nucleation Deposition freezinG Experiment) isothermal static diffusion chamber (Schrod et al, 2020). The Schrod et al (2020) results do not yield a clear seasonality but instead show that short-term variability overwhelms long-term trends. However, that observation may not represent the full picture of INP in those locations.…”

“…None of these studies presents a comprehensive analysis of continuously recorded INP data for a full seasonal cycle at one location without interruptions. Moreover, the focus of most of the previous studies, except for the Schrod et al (2020) study was especially at Arctic INPs.…”