Condensation/immersion mode ice nucleating particles in a boreal environment

Abstract

Abstract. Ice nucleating particle (INP) measurements were performed in the boreal environment of southern Finland at the Station for Measuring Ecosystem-Atmosphere Relations SMEAR II in the winter-spring of 2018. Measurements with the Portable Ice Nucleation Chamber (PINC) were conducted at 242 K and 105 % relative humidity with respect to water. The median INP number concentration [INP] during a six-week measurement period was found to be 13 L−1. [INP] spanned 3 orders of magnitude and showed a general increase from mid-February until early April. No persistent local or regional sources of INPs in the boreal environment of southern Finland could be identified. Rather, it is hypothesised that the INPs at SMEAR II are a result of dilution during long-range transport. Despite high variability, the measured [INP] values fall within the range expected for INP number concentrations measured elsewhere at similar thermodynamic conditions. [INP] did not correlate with any of the examined relevant parameters during the entire field campaign, indicating that no one single parameter can be used to predict the INP number concentration at the measurement location during the examined time period. The absence of correlation across the entire field campaign also suggests that a variety of particles are acting as INPs at different times, although it was indirectly determined that, on average, ambient INPs are most likely in the size range of 0.1–0.5 μm in diameter. On shorter time scales, several particle species correlated well with [INP] implying their potential role as INPs. Depending on the meteorological conditions, signatures of black carbon (BC), supermicron biological particles and sub-0.1 μm particles, most likely nanoscale biological fragments such as ice nucleating macromolecules (INMs), have been found in the INP signal. However, an increase in the concentration of any of these particle species may not necessarily lead to the increase in [INP], reasons for which remain unknown. Limitations of the instrumental setup and the necessity of the future field INP studies are addressed.

Sources and nature of ice-nucleating particles in the free troposphere at Jungfraujoch in winter 2017

“…Recent studies indicate the regional importance of BC particles from biomass burning events (Schill et al, 2020) and are related to mineral phases of the biomass burning particles (Jahn et al, 2020). Interestingly, BC being a tracer with appreciable correlation with [INP] has also been reported for measurements conducted in the winter in the boreal forest at Hyytiäla (Paramonov, 2020). Thus, our findings do not necessarily suggest that EC-containing particles are ice nucleation active, but other internally or externally mixed particles could potentially be the INPs, revealing that there was an anthropogenic impact on ice nucleation during this observation.…”

“…3.3.7). Laboratory studies of BC particles produced from synthetic fossil fuel are shown to be poor INPs in the immersion freezing mode for temperatures above −38 • C (Mahrt et al, 2018;Kanji et al, 2020, Friedman et al, 2011Chou et al, 2013), which questions the role of pure fossil fuel BC in ice nucleation in MPCs.…”

“…Also, primary biological particles might contribute significantly to the INP population, especially at temperatures warmer than −15 • C (Pratt et al, 2009;Schmidt et al, 2017;O'Sullivan et al, 2018), but their atmospheric contribution on a global scale is still unclear (Hoose et al, 2010;Burrows et al, 2013;Sesartic et al, 2013). Moreover, metallic particles might act as ambient INPs at MPC conditions (Cziczo et al, 2009;Kamphus et al, 2010;Ebert et al, 2011;Worringen et al, 2015) as well as aerosol particles emitted by anthropogenic sources, such as from combustion processes; however, contradictory results exist (Cozic et al, 2008;Kupiszeswski et al, 2016;Mahrt et al, 2018;Kanji et al, 2020).…”

Toward elemental analysis of ambient single particles using electrodynamic balance and laser-induced breakdown spectroscopy

“…Determining elemental composition provides crucial information about the aerosol species, sources and toxicity potential (Calvo et al 2013;Schleicher et al 2011). Thus, several studies have concluded the importance of elemental characterization of PM (e.g., Hoose and M€ ohler 2012;Kim, Kabir, and Kabir 2015;Knopf, Alpert, and Wang 2018;Paramonov et al 2019). An extensive range of analysis methods have been established for particles collected on filters or impactors, capable of analyzing a broad variety of chemical properties up to the spatial distribution of molecular composition (see, e.g., Fletcher et al 2011;Laskin et al 2003).…”

Towards parametrising atmospheric concentrations of ice nucleating particles active at moderate supercooling

“…Ice nucleating particles (INPs) affect clouds and their development by generating primary ice at temperatures between 0 and −38°C. The difficulty of understanding and thus predicting atmospheric INP concentrations ([INP]) originates from the complex interplay of their rarity, their various sources, and nucleation temperatures (Paramonov et al, 2019). A current empirical parametrisation established by DeMott et al (2015), hereafter D15, predicts [INP] based on nucleation temperature and number concentration of aerosol particles with diameters >0.5 µm ([n 0.5 ]) (DeMott et al, 2015).…”