Atmos. Chem. Phys., 13, 245–267, 2013 www.atmos-chem-phys.net/13/245/2013/ Atmospheric doi:10.5194/acp-13-245-2013 Chemistry © Author(s) 2013. CC Attribution 3.0 License. and Physics Ice nuclei in marine air: biogenic particles or dust? S. M. Burrows1,*, C. Hoose2, U. Poschl¨ 1, and M. G. Lawrence1,** 1Max Planck Institute for Chemistry, Mainz, Germany 2Institute for Meteorology and Climate Research – Atmospheric Aerosol Research, Karlsruhe Institute of Technology, Karlsruhe, Germany *now at: Pacific Northwest National Laboratory, Richland, Washington, USA **now at: Institute for Advanced Sustainability Studies e.V., Potsdam, Germany Correspondence to: S. M. Burrows ([email protected]) Received: 11 January 2012 – Published in Atmos. Chem. Phys. Discuss.: 7 February 2012 Revised: 21 November 2012 – Accepted: 27 December 2012 – Published: 11 January 2013 Abstract. Ice nuclei impact clouds, but their sources and 1 Introduction distribution in the atmosphere are still not well known. Par- ticularly little attention has been paid to IN sources in ma- The formation of ice is a crucial process in cloud develop- rine environments, although evidence from field studies sug- ment, with most precipitation globally originating in clouds gests that IN populations in remote marine regions may be containing ice. Because pure water droplets cannot freeze at ◦ dominated by primary biogenic particles associated with sea temperatures above about −40 C, ice formation in warmer spray. In this exploratory model study, we aim to bring at- clouds is initiated by airborne particles that serve as ice nu- tention to this long-neglected topic and identify promising clei (IN). Particles that are effective IN are rare, often fewer target regions for future field campaigns. We assess the likely than one out of one million airborne particles (Rosinski et al., global distribution of marine biogenic ice nuclei using a com- 1988). Current approaches to understanding global IN dis- bination of historical observations, satellite data and model tributions consider only desert dust and other continental output. By comparing simulated marine biogenic immersion sources (DeMott et al., 2010). However, certain biological IN distributions and dust immersion IN distributions, we pre- particles are also known to nucleate ice efficiently and have dict strong regional differences in the importance of marine been hypothesized to influence cloud development (Mohler¨ biogenic IN relative to dust IN. Our analysis suggests that et al., 2007). Evidence from a limited number of field stud- marine biogenic IN are most likely to play a dominant role ies suggests that a marine source of biogenic particles deter- in determining IN concentrations in near-surface-air over the mines IN abundance in air over remote, biologically active Southern Ocean, so future field campaigns aimed at investi- regions of the ocean. gating marine biogenic IN should target that region. Climate- related changes in the abundance and emission of biogenic 1.1 Evidence for a possible marine biogenic IN source marine IN could affect marine cloud properties, thereby in- troducing previously unconsidered feedbacks that influence There are two distinct lines of evidence for the existence the hydrological cycle and the Earth’s energy balance. Fur- of marine biogenic atmospheric ice nuclei, evidence coming thermore, marine biogenic IN may be an important aspect to from IN counts in the atmosphere and from laboratory testing consider in proposals for marine cloud brightening by artifi- of source material. cial sea spray production. 1. IN counts in the atmosphere: evidence from in situ observations reported in a number of studies scattered over four decades suggests that in remote, biologically active ar- eas of the ocean, the background atmospheric IN concentra- tions measured on ships are highly influenced by local ma- rine biological activity and sea spray production. Early ev- idence was provided by Bigg in 1973 (hereafter B73), who Published by Copernicus Publications on behalf of the European Geosciences Union. 246 S. M. Burrows et al.: Marine ice nuclei: biogenic particles or dust? Fig. 1. Number densities of atmospheric ice nuclei (m−3) in the marine boundary layer. Measurements by condensation-followed-by-freezing, ship-based and coastal: Australia (italic text): −15 ◦C and water saturation (Bigg, 1973). Pacific Ocean: 29 May–16 June 1985: Rosinski et al. (1987). 17 February–29 March 1984: Rosinski et al. (1987). Gulf of Mexico: Rosinski et al. (1988). East China Sea: Rosinski et al. −3 (1995). Arctic:Fig.Bigg 1. (Number1996). Antarctica: densities ofSaxena atmospheric(1983). ice Nova nuclei Scotia: (m Schnell) in the(1977 marine). Airborne boundary measurements layer. Measurements by drop freezing: by Hawaii: Schnell (1982).condensation-followed-by-freezing,Airborne measurements by continuous ship-based flow diffusion and coastalchamber:: AustraliaArctic: Rogers (italic ettext): al. ( -152001◦C); andPrenni water et al. satura-(2009b). tion (Bigg, 1973). Pacific Ocean: 29 May – 16 Jun, 1985: Rosinski et al. (1987). 17 Feb – 29 Mar, 1984: presented long-termRosinski measurementset al. (1987). Gulf of of IN Mexico: concentrations Rosinski et in al. (1988).2. EastLaboratory China Sea: testing Rosinski of source et al. (1995). material: Arctic:samples of pos- the marine boundaryBigg (1996). layer Antarctica: south of and Saxena around (1983). Australia Nova and Scotia:sible Schnell source (1977). materialAirborne can bemeasurements tested for ice by nucleation drop activity New Zealand (Bigg, 1973). Since that time, only a handful of under controlled conditions in the laboratory. Results of such freezing: Hawaii: Schnell (1982). Airborne measurements by continuous flow diffusion chamber: Arctic: further observations of marine IN concentrations have been studies for marine biogenic particles are discussed in more published (Fig.Rogers1). et In al. the (2001); B73 Prenniobservations, et al. (2009b). mean concen- detail in Sect. 1.2. Such studies can characterize the IN ac- trations of IN were generally highest around 40◦ S, a region tivity of particular species or types of particles in detail over in which rough seas are common, marine biological activ- the full temperature range of interest, however, they provide (IN). Particles that are effective IN are rare, often fewer than one out of one million airborne par- ity is strong, and large amounts of sea spray containing or- no information on which particles are present in the atmo- ganic matterticles are produced. (Rosinski It et was al., 1988). later suggested Current approaches that the tosphere, understanding their concentrations, global IN distributions distribution, consider or IN activity under source of INonly might desert be associated dust and with other the continental plankton growing sources (DeMottatmospheric et al., 2010). conditions. However, certain biological in this nutrient-rich upwelling region of the ocean (Schnell Another open question is how marine biogenic IN might and Vali, 1976particles). Further are evidence also known for ato connection nucleate ice between efficiently andbe affected have been by condensationhypothesized ofto volatileinfluence gases cloud in the marine marine biologicaldevelopment activity and(Mohler¨ marine et al.,IN concentrations 2007). Evidence was from aboundary limited number layer environement. of field studies Little suggests is known that a about the ef- uncovered in later studies: ship-based measurements in re- fects of such coating on biogenic particles, but it may dif- mote marinemarine regions source found of that biogenic atmospheric particles IN determines concentra- IN abundancefer from the in air effects over of remote, coating biologically on mineral active dust IN activity: tions were higherregions in of ocean the ocean. upwelling regions, or were asso- in one laboratory study, Chernoff and Bertram (2010) found ciated with high concentrations of biogenic materials in sam- that sulfate coatings reduced the ice nucleation activity of ples of ocean1.1 water. Evidence Physical for and a possible chemical marine analyses biogenic of IN IN sourceseveral types of mineral dust particles, but did not reduce the collected in the remote marine boundary layer of the equa- IN activity of SNOMAX, a well-known biological IN. torial Pacific Ocean showed that they were submicron-sized, There are two distinct lines of evidence for the existence of marine biogenic atmospheric ice nuclei, probably carbonaceous particles (Rosinski et al., 1987). 1.2 Candidates for marine biogenic IN It should beevidence noted that coming these historical from IN counts measurements in the atmosphere suffer and from laboratory testing of source material. from several limitations.1. IN counts Most in importantly, the atmosphere: the filterEvidence mem- fromFor in the situ purposes observations of this reported study, in we a number hypothesize of a marine brane method used at the time of those observations had sig- source of IN from “biogenic particles”. This class of parti- studies scattered over four decades suggests that in remote, biologically active areas of the ocean, nificant systematic errors; these are discussed in Sect. 3.6. cles includes “primary biological aerosol particles” (primar- Also, the link to biological acitivity is inferred primarily from ily cellular matter such as microorganisms and fungal spores, temporal or spatial correlations with biological activity in the Despres´ et al., 2012). In addition, it also includes other, non-