Abstract. Ice-nucleating particles (INPs) influence the formation of ice crystals in clouds and many types of precipitation. This study reports unique properties of INPs collected from 42 precipitation samples in the Texas Panhandle region from June 2018 to July 2019. We used a cold stage instrument called the West Texas Cryogenic Refrigerator Applied to Freezing Test system to estimate INP concentrations per unit volume of air (nINP) through immersion freezing in our precipitation samples with our detection capability of > 0.006 INP L−1. A disdrometer was used for two purposes: (1) to characterize the ground-level precipitation type and (2) to measure the precipitation intensity as well as size of precipitating particles at the ground level during each precipitation event. While no clear seasonal variations of nINP values were apparent, the analysis of yearlong ground-level precipitation observation as well as INPs in the precipitation samples showed some INP variations, e.g., the highest and lowest nINP values at −25 ∘C both in the summer for hail-involved severe thunderstorm samples (3.0 to 1130 INP L−1), followed by the second lowest at the same temperature from one of our snow samples collected during the winter (3.2 INP L−1). Furthermore, we conducted bacteria community analyses using a subset of our precipitation samples to examine the presence of known biological INPs. In parallel, we also performed metagenomics characterization of the bacterial microbiome in suspended ambient dust samples collected at commercial open-lot livestock facilities (cattle feedyards hereafter) in the Texas Panhandle (i.e., the northernmost counties of Texas, also known as “West Texas”) to ascertain whether local cattle feedyards can act as a source of bioaerosol particles and/or INPs found in the precipitation samples. Some key bacterial phyla present in cattle feedyard samples appeared in precipitation samples. However, no known ice nucleation active species were detected in our samples. Overall, our results showed that cumulative nINP in our precipitation samples below −20 ∘C could be high in the samples collected while observing > 10 mm h−1 precipitation with notably large hydrometeor sizes and an implication of cattle feedyard bacteria inclusion.

Abstract. In this study, we present atmospheric ice-nucleating particle (INP) concentrations from the Gruvebadet (GVB) observatory in Ny-Ålesund (Svalbard). All aerosol particle sampling activities were conducted in April–August 2018. Ambient INP concentrations (nINP) were measured for aerosol particles collected on filter samples by means of two offline instruments: the Dynamic Filter Processing Chamber (DFPC) and the West Texas Cryogenic Refrigerator Applied to Freezing Test system (WT-CRAFT) to assess condensation and immersion freezing, respectively. DFPC measured nINPs for a set of filters collected through two size-segregated inlets: one for transmitting particulate matter of less than 1 µm (PM1), the other for particles with an aerodynamic diameter of less than 10 µm aerodynamic diameter (PM10). Overall, nINPPM10 measured by DFPC at a water saturation ratio of 1.02 ranged from 3 to 185 m−3 at temperatures (Ts) of −15 to −22 ∘C. On average, the super-micrometer INP (nINPPM10-nINPPM1) accounted for approximately 20 %–30 % of nINPPM10 in spring, increasing in summer to 45 % at −22 ∘C and 65 % at −15 ∘C. This increase in super-micrometer INP fraction towards summer suggests that super-micrometer aerosol particles play an important role as the source of INPs in the Arctic. For the same T range, WT-CRAFT measured 1 to 199 m−3. Although the two nINP datasets were in general agreement, a notable nINP offset was observed, particularly at −15 ∘C. Interestingly, the results of both DFPC and WT-CRAFT measurements did not show a sharp increase in nINP from spring to summer. While an increase was observed in a subset of our data (WT-CRAFT, between −18 and −21 ∘C), the spring-to-summer nINP enhancement ratios never exceeded a factor of 3. More evident seasonal variability was found, however, in our activated fraction (AF) data, calculated by scaling the measured nINP to the total aerosol particle concentration. In 2018, AF increased from spring to summer. This seasonal AF trend corresponds to the overall decrease in aerosol concentration towards summer and a concomitant increase in the contribution of super-micrometer particles. Indeed, the AF of coarse particles resulted markedly higher than that of sub-micrometer ones (2 orders of magnitude). Analysis of low-traveling back-trajectories and meteorological conditions at GVB matched to our INP data suggests that the summertime INP population is influenced by both terrestrial (snow-free land) and marine sources. Our spatiotemporal analyses of satellite-retrieved chlorophyll a, as well as spatial source attribution, indicate that the maritime INPs at GVB may come from the seawaters surrounding the Svalbard archipelago and/or in proximity to Greenland and Iceland during the observation period. Nevertheless, further analyses, performed on larger datasets, would be necessary to reach firmer and more general conclusions.

No abstract

Abstract. The current inadequate understanding of ice nucleating particle (INP) sources in the Arctic region affects the uncertainty in global radiative budgets and in regional climate predictions. In this study, we present atmospheric INP concentrations by offline analyses on samples collected at ground level in Ny-Ålesund (Svalbard), in spring and summer 2018. The ice nucleation properties of the samples were characterized by means of two offline instruments: the Dynamic Filter Processing Chamber (DFPC), detecting condensation freezing INPs, and the West Texas Cryogenic Refrigerator Applied to Freezing Test system (WT-CRAFT), measuring INPs by immersion freezing. Both measurements agreed within an order of magnitude although with some notable offset. INP concentration measured by DFPC ranged 33–185 (median 88), 5–107 (50) and 3–66 (20) m−3, for T = −22, −18 and −15 °C, respectively, while at the same activation temperatures WT-CRAFT measured 3–199 (26), 1–34 (6) and 1–4 (2) m−3, with an offset apparently dependent on the INP activation temperature. This observation may indicate a different sensitivity of Arctic INPs to different ice nucleation modes, even though a contribution from measurement and/or sampling uncertainties cannot be ruled out. An increase in the coarse INP fraction was observed from spring to summer, particularly at the warmest temperature (up to ~ 70 % at −15 °C). This suggests a non-negligible contribution from local sources of biogenic aerosol particles. This conclusion is also supported by the INP temperature spectra, showing ice-forming activity at temperatures higher than −15 °C. Contrary to recent works (e.g., INP measurements from Ny-Ålesund in 2012), our results do not show a sharp spring-to-summer increase of the INP concentration, with distinct behaviors for particles active in different temperature ranges. This likely indicates that the inter-annual variability of conditions affecting the INP emission by local sources may be wider than previously considered and suggests a complex interplay between INP sources. This demonstrate the necessity of further data coverage. Analysis of INP concentrations, active site density, low-travelling back-trajectories (

In this study, we have segregated our precipitation samples into four different categories, such as (1) snows, (2) hails/thunderstorms, (3) long-lasted rains, and (4) weak rains. For this categorization, we have considered both our observation-based as well as the disdrometer-assigned National Weather Service (NWS) code. Initially, the precipitation samples had been assigned one of the four categories based on our manual observation. In the next step, we have used each NWS code and its occurrence in each precipitation sample to finalize the precipitation category. During this step, a precipitation sample was categorized into snow, only when we identified a snow type NWS code (Snow: S-, S, S+ and/or Snow Grains: SG). Likewise, a precipitation sample was categorized into hail/thunderstorm, only when the cumulative sum of NWS codes for hail was counted more than five times (i.e., A + SP ≥ 5; where A and SP are the codes for soft hail and hail, respectively). This limit of five was chosen arbitrarily. If there existed no snow and/or hail type NWS codes, we defined the category as we observed, thus falling in either long-lasted or weak rain category. Overall, in this study we acquired 6 snow, 18 hail/thunderstorm, 13 long-lasted, and 5 weak rain samples for the sampling period of June 2018-July 2019. Table S1-1 gives the detailed information about the collected precipitation samples. The ID # column goes from 1-42. The column of 'Sample#' is the precipitation sample number in the chronological order. The missing precipitation sample numbers are the ones collected negligible amount of precipitation (typically < 1 ml). This amount is too small to carry out the West Texas Cryogenic Refrigerator Applied to Freezing Test (WT-CRAFT) ice-nucleating particle (INP) measurements. The amount of precipitation collected (in ml) is presented in Table S1-1. Table S1-1 also includes the season in which each precipitation was observed and collected. Table S1-1. Summary of the Precipitation Categories and sampling periods. ID# Sample# Start Date (Local Time) End Date (Local Time) Season Volume Collected (ml) NWS Code* Precipitation Type 1