Abstract
Abstract. Ice nucleation in the atmosphere is central to the understanding the microphysical properties of mixed-phase and cirrus clouds. Ambient conditions such as temperature (T) and relative humidity (RH), as well as aerosol properties such as chemical composition and mixing state play an important role in predicting ice formation in the troposphere. Previous field studies have reported the absence of sulfate and organic compounds on mineral dust ice crystal residuals sampled at mountain top stations or aircraft based measurements despite the long-range transport mineral dust is subjected to. We present laboratory studies of ice nucleation for immersion and deposition mode on ozone aged mineral dust particles for 233 < T < 263 K. Heterogeneous ice nucleation of untreated kaolinite (Ka) and Arizona Test Dust (ATD) particles is compared to corresponding aged particles that are subjected to ozone concentrations of 0.4–4.3 ppmv in a stainless steel aerosol tank. The portable ice nucleation counter (PINC) and immersion chamber combined with the Zurich ice nucleation chamber (IMCA-ZINC) are used to conduct deposition and immersion mode measurements, respectively. Ice active fractions as well as ice active surface site densities (ns) are reported and observed to increase as a function of decreasing temperature. We present first results that demonstrate enhancement of the ice nucleation ability of aged mineral dust particles in both the deposition and immersion mode due to ageing. We also present the first results to show a suppression of heterogeneous ice nucleation activity without the condensation of a coating of (in)organic material. In immersion mode, low ozone exposed Ka particles showed enhanced ice activity requiring a median freezing temperature of 1.5 K warmer than that of untreated Ka, whereas high ozone exposed ATD particles showed suppressed ice nucleation requiring a median freezing temperature of 3 K colder than that of untreated ATD. In deposition mode, low exposure Ka had ice active fractions of an order of magnitude higher than untreated Ka, whereas high ozone exposed ATD had ice active fractions up to a factor of 4 lower than untreated ATD. From our results, we derive and present parameterizations in terms of ns(T) that can be used in models to predict ice nuclei concentrations based on available aerosol surface area.
Highlights
Previous field studies have reported the absence of sulfate and organic compounds on mineral dust ice crystal residuals sampled at mountain top stations or aircraft based measureour results, we derive and prMeseentthpoadrasmeatenridzations in terms of ns(T ) that can centrations based boenuasveadiliaDnbmlaeotaadeerloSssytoolspstureerfdmaiccset iacreean.uclei conments despite the long-range transport mineral dust is subjected to
Uptake coefficients (γ ) determined for the above ageing experiments were found to be of the order of 10−5 and 10−4 for kaolinite and Arizona Test Dust, respectively which are in agreement with previous values reported in the literature
We present parameterizations of ice-active fractions and surface densities as a function of temperature for both ice nucleation modes that can be used for comparison to other studies and for implementation in ice nucleation modelling
Summary
Previous field studies have reported the absence of sulfate and organic compounds on mineral dust ice crystal residuals sampled at mountain top stations or aircraft based measureour results, we derive and prMeseentthpoadrasmeatenridzations in terms of ns(T ) that can centrations based boenuasveadiliaDnbmlaeotaadeerloSssytoolspstureerfdmaiccset iacreean.uclei conments despite the long-range transport mineral dust is subjected to. We present laboratory studies of ice nucleation for immersion and deposition mode on ozone aged mineral dust particles for 233 < T < 263 K. M of untreated kaolinite (Ka) and Arizona Test Dust (ATD) particles is compared to corresponding aged particles that are Ice crystals form in tropospheric clouds through homogesubjected to ozone concentrations of 0.4–4.3 ppmv in a stain- neous and heterogeneous nucleation mechanisms. We present first results that demon- is necessary in order to appropriately treat the process in strate enhancement of the ice nucleation ability of aged mineral dust particles in both the deposition and immersion mode gtiloonbsalincitrhceultartoipoonsmphoedrOeelscfoaernaad nnpuremSdbiccetireiocnef crcereayssotanls.coFnircsetn, tarac--. In immer- sphere since ice is an important sink of gas phase water, an sion mode, low ozone exposed Ka particles showed enhanced especially active green-house gas in the upper troposphere ice activity requiring a median freezing temperature of 1.5 K (Lindzen, 1990). IcSe aocltisdasEaasrutrhface for heterowarmer than that of untreated Ka, whereas high ozone ex- geneous chemistry through the uptake of many trace gases (Kolb et al, 2010; Abbatt, 2003), for example, SO2 and O3, Published by Copernicus Publications on behalf of the European Geosciences Union
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