Heterogeneous ice nucleation and water uptake by field‐collected atmospheric particles below 273 K

Abstract

Ice formation induced by atmospheric particles through heterogeneous nucleation is not well understood. Onset conditions for heterogeneous ice nucleation and water uptake by particles collected in Los Angeles and Mexico City were determined as a function of temperature (200–273 K) and relative humidity with respect to ice (RHice). Four dominant particle types were identified including soot associated with organics, soot with organic and inorganics, inorganic particles of marine origin coated with organic material, and Pb/Zn‐containing particles apportioned to emissions relevant to waste incineration. Single particle characterization was provided by micro‐spectroscopic analyses using computer controlled scanning electron microscopy with energy dispersive analysis of X‐rays (CCSEM/EDX) and scanning transmission X‐ray microscopy with near edge X‐ray absorption fine structure spectroscopy (STXM/NEXAFS). Above 230 K, significant differences in onsets of water uptake and immersion freezing of different particle types were observed. Below 230 K, particles exhibited high deposition ice nucleation efficiencies and formed ice atRHicewell below homogeneous ice nucleation limits. The data suggest that water uptake and immersion freezing are more sensitive to changes in particle chemical composition compared to deposition ice nucleation. The data demonstrate that anthropogenic and marine influenced particles, exhibiting various chemical and physical properties, possess distinctly different ice nucleation efficiencies and can serve as efficient IN at atmospheric conditions typical for cirrus and mixed‐phase clouds.

Direct observation of ice nucleation events on individual atmospheric particles

“…The ambient particle sample was collected with a MOUDI (8th stage with 50% cut-off diameter of 0.32 mm) at the ground sampling site during the California Research at the Nexus of Air Quality and Climate Change (CalNex) campaign on May 19, 2010 (12 am to 6 am). 20 …”

“…The onset values are consistent with our previous OM observations over particles collected at the same location, time, and with similar total particle surface areas for ice nucleation (0.15 vs. 0.26 mm 2 ). 20 Fig. 8 illustrates the identification of the INPs in the field-collected sample.…”

“…ESEM, equipped with an EDAX X-ray spectrometer with a Si(Li) detector with a 10 mm 2 active area and an ATW2 window, was used to determine the size, surface area, morphology, and elemental composition of individual particles including the INPs. [19][20][21] X-ray analysis of the identified INPs was acquired at an acceleration voltage of 20 kV and a beam current of 430 pA. Elemental compositions of INPs were determined from the recorded X-ray spectra. More details on the SEM/ EDX analysis and X-ray mapping of individual particles are reported elsewhere.…”

“…[12][13][14][15][16][17][18] Hence, it represents a significant improvement over more commonly used optical microscopy (OM) approaches. [19][20][21][22][23][24][25] Complemented with X-rays microanalysis, ESEM has the potential to conduct microscopy studies of ice nucleation along with chemical characterization of the INPs. Currently, the limiting factor for ESEM ice nucleation experiments is the ability to accurately control temperature and relative humidity (RH) above the sample over a broad range of freezing temperatures.…”

Facile Method for Determining the Aspect Ratios of Mineral Dust Aerosol by Electron Microscopy

“…Mineral dust is one of the most common ice nuclei, and aluminosilicate clay minerals are one of the most ice-active types of mineral dust (Broadley et al 2012;Pinti et al 2012). Ice nuclei from field samples have been studied in great detail using scanning electron microscopy (SEM) and scanning transmission X-ray microscopy (STXM; Wang et al 2012;Hiranuma et al 2013). Among mineral dust components, clay minerals have the largest aspect ratios, with disklike shapes and measured aspect ratios of approximately 4 to 500 (Nadeu 1985;Inoue and Kitagawa 1994).…”