Biological residues define the ice nucleation properties of soil dust

Abstract

Soil dust is a major driver of ice nucleation in clouds leading to precipitation. It consists largely of mineral particles with a small fraction of organic matter constituted mainly of remains of micro-organisms that participated in degrading plant debris before their own decay. Some micro-organisms have been shown to be much better ice nuclei than the most efficient soil mineral. Yet, current aerosol schemes in global climate models do not consider a difference between soil dust and mineral dust in terms of ice nucleation activity. Here, we show that particles from the clay and silt size fraction of four different soils naturally associated with 0.7 to 11.8 % organic carbon (w/w) can have up to four orders of magnitude more ice nuclei per unit mass active in the immersion freezing mode at −12 °C than montmorillonite, the most efficient pure clay mineral. Most of this activity was lost after heat treatment. Removal of biological residues reduced ice nucleation activity to, or below that of montmorillonite. Desert soils, inherently low in organic content, are a large natural source of dust in the atmosphere. In contrast, agricultural land use is concentrated on fertile soils with much larger organic matter contents than found in deserts. It is currently estimated that the contribution of agricultural soils to the global dust burden is less than 20 %. Yet, these disturbed soils can contribute ice nuclei to the atmosphere of a very different and much more potent kind than mineral dusts

Biogenic ice nuclei in boundary layer air over two U.S. High Plains agricultural regions

“…At Grant Family Farms, IN concentrations were lower, and bacteria with the ina gene were at or below the detection limit, and below the concentration of IN at −12°C for the four cases studied. Despite the relative absence of INA bacteria, the data suggest the abundant presence of apparent biological IN [ Conen et al , 2011; Schnell and Vali , 1976]. These biological particles remain to be completely identified.…”

“…as IN also lose all activity above −12°C when heated to 90°C for 10 min [ Pouleur et al , 1992], and lichen as IN are sensitive to heating to >70°C [ Kieft and Ruscetti , 1990], suggesting their ice nucleating proteins are similarly heat labile. While heat treatment is expected to inactivate biological IN [ Christner et al , 2008], it is not expected to affect the ice nucleation activity of inorganic materials, such as mineral dust [e.g., Conen et al , 2011]. Cumulative numbers of IN per milliliter Biosampler water were estimated using the formula where f is the proportion of droplets not frozen and V the volume of each aliquot [ Vali , 1971], and using the total water volume and volume of air sampled converted to IN per standard liter of air.…”

“…Soil dust generated by agricultural activities contains aerosolized minerals, microorganisms, and organic matter. The contribution of nonmicrobial soil organic matter as a potential atmospheric IN source has long been postulated [ Schnell and Vali , 1972] but surprisingly remains unresolved, though recently implicated [ Conen et al , 2011]. Although mineral dust is known to impact atmospheric ice nucleation [ Cziczo et al , 2004; DeMott et al , 2003; Richardson et al , 2007], laboratory [ Broadley et al , 2012; Connolly et al , 2009; DeMott et al , 2011] and field measurements [ Ansmann et al , 2008] suggest that colder temperatures are required for significant ice nucleation to occur on dust, compared to ice nucleation by certain biological particles.…”

Marine and terrestrial influences on ice nucleating particles during continuous springtime measurements in an Arctic oilfield location

“…Immersion freezing is the most relevant to MPC formation and requires that INPs initially serve as CCN. Aerosols such as mineral dust, soil dust, sea salt, volcanic ash, black 10 carbon from wildfires, and primary biological aerosol particles (PBAPs) have been shown to serve as INPs (Coluzza et al, 2017;Conen et al, 2011;DeMott et al, 1999;Hoose and Möhler, 2012;McCluskey et al, 2014;Murray et al, 2012;Petters et al, 2009). Among these, dust and PBAPs are the most adroit INPs found in the atmosphere (Coluzza et al, 2017;Murray et al, 2012).…”

“…PBAPs originating from certain bacteria and vegetative detritus are the most efficient INPs known, capable of initiating freezing near −1°C, while most PBAPs (e.g., pollen, fungal spores, algae, and diatoms) tend to nucleate ice at 15 temperatures similar to those of mineral dust but warmer than sea salt or volcanic ash (Alpert et al, 2011;Creamean et al, 2014;Creamean et al, 2013;Despres et al, 2012;Durant et al, 2008;Fröhlich-Nowoisky et al, 2015;Hader et al, 2014b;Hill et al, 2016;Hoose and Möhler, 2012;Knopf et al, 2010;McCluskey et al, 2014;Murray et al, 2012;O'Sullivan et al, 2014;Tesson et al, 2016;Tobo et al, 2014;Umo et al, 2015). However, dusts can serve as atmospheric shuttles for small microbes, enabling these particle mixtures to behave more efficiently as INPs compared to the dust alone (Conen et al, 2011;20 Creamean et al, 2013;O'Sullivan et al, 2014). Consequently, PBAPs have the potential to play a crucial role in cloud ice formation (Creamean et al, 2014;Creamean et al, 2013;Pratt et al, 2009) and precipitation enhancement (Bergeron, 1935;Christner et al, 2008;Morris et al, 2014;Morris et al, 2004;Morris et al, 2017;Stopelli et al, 2014), particularly in the presence of supercooled water or large cloud droplets.…”