The study of atmospheric ice-nucleating particles via microfluidically generated droplets

Abstract

Ice-nucleating particles (INPs) play a significant role in the climate and hydrological cycle by triggering ice formation in supercooled clouds, thereby causing precipitation and affecting cloud lifetimes and their radiative properties. However, despite their importance, INP often comprise only 1 in 103–106 ambient particles, making it difficult to ascertain and predict their type, source, and concentration. The typical techniques for quantifying INP concentrations tend to be highly labour-intensive, suffer from poor time resolution, or are limited in sensitivity to low concentrations. Here, we present the application of microfluidic devices to the study of atmospheric INPs via the simple and rapid production of monodisperse droplets and their subsequent freezing on a cold stage. This device offers the potential for the testing of INP concentrations in aqueous samples with high sensitivity and high counting statistics. Various INPs were tested for validation of the platform, including mineral dust and biological species, with results compared to literature values. We also describe a methodology for sampling atmospheric aerosol in a manner that minimises sampling biases and which is compatible with the microfluidic device. We present results for INP concentrations in air sampled during two field campaigns: (1) from a rural location in the UK and (2) during the UK’s annual Bonfire Night festival. These initial results will provide a route for deployment of the microfluidic platform for the study and quantification of INPs in upcoming field campaigns around the globe, while providing a benchmark for future lab-on-a-chip-based INP studies.Electronic supplementary materialThe online version of this article (10.1007/s10404-018-2069-x) contains supplementary material, which is available to authorized users.

Development of the DRoplet Ice Nuclei Counter Zurich (DRINCZ): validation and application to field-collected snow samples

“…In contrast bulk methods such as drop-freezing assays (Hill et al, 2014;Stopelli et al, 2014;Vali, 1971), differential scanning calorimetry (Kaufmann et al, 2016;Pinti et al, 2012) and microfluidic devices (Reicher et al, 2018;Riechers et al, 2013;Stan et al, 2009;Tarn et al, 2018) immerse the samples in water and can be used to detect lower atmospheric INP concentrations. The majority of atmospheric INP concentrations at temperatures above −15 • C have been quantified using drop-freezing assays.…”

“…The majority of atmospheric INP concentrations at temperatures above −15 • C have been quantified using drop-freezing assays. To retrieve the concentrations of INP from such bulk suspensions, Vali (1971Vali ( , 2019 showed that by dividing a sample into several aliquots, it is possible to calculate the number of INPs present in the sample as a function of temperature. The probability for more than one INP in an aliquot that freezes at the same temperature can be predicted using Poisson's law (Vali, 1971).…”

“…To retrieve the concentrations of INP from such bulk suspensions, Vali (1971Vali ( , 2019 showed that by dividing a sample into several aliquots, it is possible to calculate the number of INPs present in the sample as a function of temperature. The probability for more than one INP in an aliquot that freezes at the same temperature can be predicted using Poisson's law (Vali, 1971). Following Vali (1971), the cumulative number of INPs in a given sample for each temperature can be calculated as…”

“…The probability for more than one INP in an aliquot that freezes at the same temperature can be predicted using Poisson's law (Vali, 1971). Following Vali (1971), the cumulative number of INPs in a given sample for each temperature can be calculated as…”

“…Studies have investigated the concentrations of INPs in the atmosphere over the last 50 years and show that the concentration in the atmosphere spans several orders of magnitude (Fletcher, 1962;Kanji et al, 2017;Petters and Wright, 2015;Welti et al, 2018). Some of the original studies investigated the INP concentrations in melted hail and snow samples (e.g., Vali, 1971). Since then, studies have diversified to sample INPs directly from the air (Boose et al, 2016b;Creamean et al, 2013;DeMott et al, 2003;Lacher et al, 2017;Richardson et al, 2007;Welti et al, 2018) and from precipitation (Christner et al, 2008;Hill et al, 2014;Petters and Wright, 2015;Stopelli et al, 2015) and investigated potential types of INPs in the laboratory from commercial and naturally occurring samples as well as field-collected samples (Atkinson et al, 2013;Boose et al, 2016a;Broadley et al, 2012;Felgitsch et al, 2018;Hill et al, 2014;Hiranuma et al, 2015Hiranuma et al, , 2019Kaufmann et al, 2016;Murray et al, 2012;Pummer et al, 2012;Wex et al, 2015).…”