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 6-week measurement period was 13 L−1. The [INP] spanned 3 orders of magnitude and showed a general increase from mid-February until early April. No single dominant local or regional sources of INPs in the boreal environment of southern Finland could be identified. Rather, it is hypothesised that the INPs detected at SMEAR II are a result of long-range transport and dilution of INPs sourced far from the measurement site. Despite high variability, the measured [INP] values fall within the range expected for the [INP] measured elsewhere under similar thermodynamic conditions. The [INP] did not correlate with any of the examined parameters during the entire field campaign, indicating that no one single parameter can be used to predict the [INP] at the measurement location during the examined time period. The absence of a correlation across the entire field campaign also suggests that a variety of particles act as INPs at different times, although it was indirectly determined that ambient INPs are most likely within the size range of 0.1–0.5 µm in diameter on average. On shorter timescales, several particle species correlated well with the [INP]. Depending on the meteorological conditions, black carbon (BC), supermicron biological particles and sub-0.1 µm particles, most likely nanoscale biological fragments such as ice-nucleating macromolecules (INMs), correlated with the INP signal. However, an increase in the concentration of any of these particle species may not necessarily lead to the increase in the [INP]; the reasons for this remain unknown. Limitations of the instrumental set-up and the necessity for future field INP studies are addressed.

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

“…The first comprehensive ice nucleation campaign at 80 SMEARII called HyICE-2018 took place from February 2018 to June 2018. First results from HyICE-2018 are published in Paramonov et al (2020), who show INP measurements with a continuous flow diffusion chamber (CFDC) during the first part of the HyICE-2018 campaign from 19 February 2018 to 2 April 2018. In this paper, we present the results of filter-based INP https://doi.org/10.5194/acp-2020-683 Preprint.…”

“…A detailed description of the set-up and working principle of the L-Tof-AMS during the HyICE-2018 campaign can be found in Paramonov et al (2020).…”

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

“…The excitation pulses are fired into the sample volume at different times, and both detection channels record the emission(s) from both excitations, leading to three distinguishable excitation-emission combinations (the 370 nm light saturates the 310-400 nm detection channel and, therefore, does not provide any information). Thus, the fluorescence can be divided into the following seven unique fluorescence groups based on the excitation-emission wavelength pairs and their combinations after Perring et al (2015) and Savage et al 2017: A (only FL1 -excitation 280 nm; emission 310-400 nm), B (only FL2 -excitation 280 nm; emission 420-650 nm), C (only FL3 -excitation 370 nm; emission 420-650 nm), AB (FL1 and FL2), BC (FL2 and FL3), AC (FL1 and FL3) and ABC (FL1 and FL2 and FL3). The WIBS performs an empty chamber background signal check every 8 h, during which the excitation pulses are fired into the optical chamber without any present particles.…”

“…Furthermore, the stricter threshold only marginally affects the detection efficiency of biological particles because they tend to have stronger fluorescence (Savage et al, 2017). More detailed descriptions on the WIBS are also available in Savage et al (2017) and Perring et al (2015). Daily size distributions measured by the DMPS and APS combination are compared with the size distributions measured by the WIBS from 11 March to 13 May 2018 and are shown in Fig.…”

“…The first comprehensive ice nucleation campaign at SMEARII, called HyICE-2018, took place from February to June 2018. The first results from HyICE-2018 are published in Paramonov et al (2020), who show INP measurements with a continuous flow diffusion chamber (CFDC) during the first part of the HyICE-2018 campaign from 19 February to 2 April 2018. Here, we present the results of filter-based INP measurements, which provide a continuous record from 11 March to 13 May 2018, with a consistent time resolution of 24 h. After these 2 intensive sampling months during the HyICE-2018 campaign, the INP measurements were continued until 31 May 2019 with a time resolution of mostly 48 or 72 h, and only in a few cases with sample time intervals of up to 144 h. By this, we obtained a continuous long-term record of INP temperature spectra from 11 March 2018 to 31 May 2019.…”