Size-resolved measurements of ice-nucleating particles at six locations in North America and one in Europe

Abstract

Abstract. Detailed information on the size of ice-nucleating particles (INPs) may be useful in source identification, modeling their transport in the atmosphere to improve climate predictions, and determining how effectively or ineffectively instrumentation used for quantifying INPs in the atmosphere captures the full INP population. In this study we report immersion-mode INP number concentrations as a function of size at six ground sites in North America and one in Europe using the micro-orifice uniform-deposit impactor droplet freezing technique (MOUDI-DFT), which combines particle size-segregation by inertial impaction and a microscope-based immersion freezing apparatus. The lowest INP number concentrations were observed at Arctic and alpine locations and the highest at suburban and agricultural locations, consistent with previous studies of INP concentrations in similar environments. We found that 91 ± 9, 79 ± 17, and 63 ± 21 % of INPs had an aerodynamic diameter > 1 µm at ice activation temperatures of −15, −20, and −25 °C, respectively, when averaging over all sampling locations. In addition, 62 ± 20, 55 ± 18, and 42 ± 17 % of INPs were in the coarse mode (> 2.5 µm) at ice activation temperatures of −15, −20, and −25 °C, respectively, when averaging over all sampling locations. These results are consistent with six out of the nine studies in the literature that have focused on the size distribution of INPs in the atmosphere. Taken together, these findings strongly suggest that supermicron and coarse-mode aerosol particles are a significant component of the INP population in many different ground-level environments. Further size-resolved studies of INPs as a function of altitude are required since the size distribution of INPs may be different at high altitudes due to size-dependent removal processes of atmospheric particles.

Comparative measurements of ambient atmospheric concentrations of ice nucleating particles using multiple immersion freezing methods and a continuous flow diffusion chamber

“…4b), and the underestimate of INP concentrations due to the elimination of coarse-mode aerosols in CFDC sampling ranges from about 2 to 4 times (see MOUDI "all" vs. "size" in Fig. 4b), consistent with the estimates of coarse-mode INP fractions by Mason et al (2016). We may note similarly good agreement between INP concentrations measured by the CFDC and DFT methods across similar temperature ranges for marine aerosols .…”

Potential of polarization lidar to provide profiles of CCN- and INP-relevant aerosol parameters

“…Strong differences in the INP efficacy of different aerosol types is found in laboratory studies (see review of Murray et al, 2012). Furthermore, observations also indicate that particles with radii < 250 nm may be activated as well (Mason et al, 2016). The size effect was found to increase with decreasing temperature.…”

Characterization of free amino acids, bacteria and fungi in size-segregated atmospheric aerosols in boreal forest: seasonal patterns, abundances and size distributions

“…S7). There is some evidence that cloud-active particles larger than ∼ 1 µm are biological in origin (Haga et al, 2014;Hassett et al, 2015;Mason et al, 2016;Möhler et al, 2007), and in mixedphase cloud conditions, PBAPs may play an important role in triggering rainfall. Collectively, the different correlations observed between rainfall and PBAP components suggest that a potential feedback mechanism may persist at the boreal forest.…”