scholarly journals Glass formation and unusual hygroscopic growth of iodic acid solution droplets with relevance for iodine mediated particle formation in the marine boundary layer

2012 ◽  
Vol 12 (18) ◽  
pp. 8575-8587 ◽  
Author(s):  
B. J. Murray ◽  
A. E. Haddrell ◽  
S. Peppe ◽  
J. F. Davies ◽  
J. P. Reid ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Acid Solution ◽  
Marine Boundary Layer ◽  
Fine Particles ◽  
Cloud Condensation Nuclei ◽  
Amorphous Material ◽  
Amorphous State ◽  
Hygroscopic Growth ◽  
Condensation Nuclei ◽  
Iodic Acid

Abstract. Iodine oxide particles are known to nucleate in the marine boundary layer where gas phase molecular iodine and organoiodine species are produced by macroalgae. These ultra-fine particles may then grow through the condensation of other materials to sizes where they may serve as cloud condensation nuclei. There has been some debate over the chemical identity of the initially nucleated particles. In laboratory simulations, hygroscopic measurements have been used to infer that they are composed of insoluble I2O4, while elemental analysis of laboratory generated particles suggests soluble I2O5 or its hydrated form iodic acid, HIO3 (I2O5·H2O). In this paper we explore the response of super-micron sized aqueous iodic acid solution droplets to varying humidity using both Raman microscopy and single particle electrodynamic traps. These measurements reveal that the propensity of an iodic acid solution droplet to crystallise is negligible on drying to ~0% relative humidity (RH). On applying mechanical pressure to these droplets they shatter in a manner consistent with an ultra-viscous liquid or a brittle glass. Water retention in amorphous material at low RH is important for understanding the hygroscopic growth of aerosol particles and uptake of other condensable material. Subsequent water uptake between 10 and 20% RH causes their viscosity to reduce sufficiently that the cracked droplets flow and merge. The persistence of iodic acid solution in an amorphous state, rather than a crystalline state, suggests they will more readily accommodate other condensable material and are therefore more likely to grow to sizes where they may serve as cloud condensation nuclei. On increasing the humidity to ~90% the mass of the droplets only increases by ~20% with a corresponding increase in radius of only 6%, which is remarkably small for a highly soluble material. We suggest that the small growth factor of aqueous iodic acid solution droplets is consistent with the small aerosol growth factors observed in previous experiments.

scholarly journals Glass formation and unusual hygroscopic growth of iodic acid solution droplets with relevance for iodine oxide particles in the coastal marine boundary layer

2012 ◽  
Vol 12 (3) ◽  
pp. 7879-7908 ◽  
Author(s):  
B. J. Murray ◽  
A. E. Haddrell ◽  
S. Peppe ◽  
J. F. Davies ◽  
J. P. Reid ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Acid Solution ◽  
Field Experiments ◽  
Marine Boundary Layer ◽  
Cloud Condensation Nuclei ◽  
Amorphous State ◽  
Hygroscopic Growth ◽  
Mechanical Pressure ◽  
Iodic Acid ◽  
Oxide Particles

Abstract. Iodine oxide particles are known to nucleate in the marine boundary layer where gas phase molecular iodine and organoiodine species are produced by macroalgae. There has been some debate over the chemical identity of these particles. Hygroscopic measurements have been used to infer that they are composed of insoluble I2O4, while elemental analysis of laboratory generated particles suggests soluble I2O5 or its hydrated form iodic acid, HIO3 (I2O5 · H2O). In this paper we explore the response of super-micron sized aqueous iodic acid solution droplets to varying humidity using both Raman microscopy and single particle electrodynamic traps. These measurements reveal that the propensity of an iodic acid solution droplet to crystallise is negligible on drying to ~0% relative humidity (RH). On applying mechanical pressure to these droplets they shatter in a manner consistent with an ultra-viscous liquid or a brittle glass, but subsequent water uptake between 10 and 20% RH causes their viscosity to reduce sufficiently that the cracked droplets flow and merge. The persistence of iodic acid solution in an amorphous state, rather than a crystalline state, suggests they will more readily accommodate other condensable material and are therefore more likely to grow to sizes where they may serve as cloud condensation nuclei. On increasing the humidity to ~90% the mass of the droplets only increases by ~20% with a corresponding increase in radius of only ~6 %, which is remarkably small for a highly soluble material. We suggest that the small growth factor of aqueous iodic acid solution droplets is consistent with the small aerosol growth factors observed in field experiments.

scholarly journals Manipulating marine stratocumulus cloud amount and albedo: a process-modelling study of aerosol-cloud-precipitation interactions in response to injection of cloud condensation nuclei

2011 ◽  
Vol 11 (1) ◽  
pp. 885-916 ◽  
Author(s):  
H. Wang ◽  
P. J. Rasch ◽  
G. Feingold
Keyword(s):  
Boundary Layer ◽  
Liquid Water ◽  
Marine Boundary Layer ◽  
Cloud Condensation Nuclei ◽  
Cloud Amount ◽  
Number Concentration ◽  
Condensation Nuclei ◽  
Liquid Water Path ◽  
Water Path ◽  
Injection Method

Abstract. We use a cloud-system-resolving model to study marine-cloud brightening. We examine how injected aerosol particles that act as cloud condensation nuclei (CCN) are transported within the marine boundary layer and how the additional particles in clouds impact cloud microphysical processes, and feedback on dynamics. Results show that the effectiveness of cloud brightening depends strongly on meteorological and background aerosol conditions. Cloud albedo enhancement is very effective in a weakly precipitating boundary layer and in CCN-limited conditions preceded by heavy and/or persistent precipitation. The additional CCN help sustain cloud water by weakening the precipitation substantially in the former case and preventing the boundary layer from collapse in the latter. For a given amount of injected CCN, the injection method (i.e., number and distribution of sprayers) is critical to the spatial distribution of these CCN. Both the areal coverage and the number concentration of injected particles are key players but neither one always emerges as more important than the other. The same amount of injected material is much less effective in either strongly precipitating clouds or polluted clouds, and it is ineffective in a relatively dry boundary layer that supports clouds of low liquid water path. In the polluted case and "dry" case, the CCN injection increases drop number concentration but lowers supersaturation and liquid water path. As a result, the cloud experiences very weak albedo enhancement, regardless of the injection method.

scholarly journals Fast sulfur dioxide measurements correlated with cloud condensation nuclei spectra in the marine boundary layer

2011 ◽  
Vol 11 (22) ◽  
pp. 11511-11519 ◽  
Author(s):  
D. C. Thornton ◽  
A. R. Bandy ◽  
J. G. Hudson
Keyword(s):  
Boundary Layer ◽  
Sulfur Dioxide ◽  
Marine Boundary Layer ◽  
Cloud Condensation Nuclei ◽  
High Rate ◽  
Condensation Nuclei ◽  
Convective Boundary ◽  
Shallow Cumulus ◽  
First Time ◽  
Linear Correlations

Abstract. During the Rain in (shallow) Cumulus over the Ocean (RICO) project simultaneous high rate sulfur dioxide (SO2) measurements and cloud condensation nuclei (CCN) spectra were made for the first time. For research flight 14 (14 January 2005) the convective boundary layer was impacted by precipitation and ship plumes for much of the midday period but not in the late afternoon. Number densities of accumulation mode aerosols (0.14 to 0.2 μm diameter) were a factor of two greater in the later period while CCN were 35% to 80% greater for aerosols that activate at supersaturations >0.1%. Linear correlations of SO2 and CCN were found for SO2 concentrations ranging from 20 to 600 parts-per-trillion (pptv). The greatest sensitivities were for SO2 and CCN that activate at supersaturations >0.1% for both clean and polluted air. In a region unaffected by pollution SO2 was linearly correlated only with CCN at >0.2% supersaturation. These correlations imply that the smallest CCN may be activated by SO2 through heterogeneous conversion. Evidence for entrainment of CCN from the cloud layer into the CBL was found.

scholarly journals Properties of cloud condensation nuclei (CCN) in the trade wind marine boundary layer of the western North Atlantic

2016 ◽  
Vol 16 (4) ◽  
pp. 2675-2688 ◽  
Author(s):  
Thomas B. Kristensen ◽  
Thomas Müller ◽  
Konrad Kandler ◽  
Nathalie Benker ◽  
Markus Hartmann ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Long Range ◽  
North Atlantic ◽  
Particle Number ◽  
Marine Boundary Layer ◽  
Mineral Dust ◽  
Cloud Condensation Nuclei ◽  
Sea Salt ◽  
Condensation Nuclei ◽  
Accumulation Mode

Abstract. Cloud optical properties in the trade winds over the eastern Caribbean Sea have been shown to be sensitive to cloud condensation nuclei (CCN) concentrations. The objective of the current study was to investigate the CCN properties in the marine boundary layer (MBL) in the tropical western North Atlantic, in order to assess the respective roles of inorganic sulfate, organic species, long-range transported mineral dust and sea-salt particles. Measurements were carried out in June–July 2013, on the east coast of Barbados, and included CCN number concentrations, particle number size distributions and offline analysis of sampled particulate matter (PM) and sampled accumulation mode particles for an investigation of composition and mixing state with transmission electron microscopy (TEM) in combination with energy-dispersive X-ray spectroscopy (EDX). During most of the campaign, significant mass concentrations of long-range transported mineral dust was present in the PM, and influence from local island sources can be ruled out. The CCN and particle number concentrations were similar to what can be expected in pristine marine environments. The hygroscopicity parameter κ was inferred, and values in the range 0.2–0.5 were found during most of the campaign, with similar values for the Aitken and the accumulation mode. The accumulation mode particles studied with TEM were dominated by non-refractory material, and concentrations of mineral dust, sea salt and soot were too small to influence the CCN properties. It is highly likely that the CCN were dominated by a mixture of sulfate species and organic compounds.

Formation Pathways and Composition of Iodine Oxide Ultra-Fine Particles

2005 ◽  
Vol 2 (4) ◽  
pp. 299 ◽  
Author(s):  
Russell W. Saunders ◽  
John M. C. Plane
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Fine Particles ◽  
Cloud Condensation Nuclei ◽  
Rate Coefficients ◽  
Particle Nucleation ◽  
Major Pathway ◽  
Coastal Marine ◽  
Transmission Electron ◽  
Ultra Fine Particles

Environmental Context.Bursts of ultra-fine particles (diameter < 10 nm) in the daytime coastal marine boundary layer at low tide coincide with the observation of iodine oxide radicals. The detection of iodine in the particles suggests a direct link between the biogenic emission of iodine-containing vapours and subsequent particle nucleation and growth. These coastal aerosols are therefore most likely iodine oxide polymers. However, the reaction pathways leading to the homogeneous nucleation of these particles are currently an area of uncertainty, as is their final composition. These ultra-fine particles are potentially important as a source of cloud condensation nuclei, and as a major pathway for enriching iodine in marine aerosol. Abstract.Iodine oxide nanoparticles were generated photochemically from I2 in the presence of O3, and their morphology and composition analyzed by transmission electron microscopy (TEM). The particles exhibit fractal morphologies consistent with agglomerative coagulation, and have an O/I ratio of 2.45 ± 0.08, indicating that they are composed of I2O5. Quantum calculations show that gas-phase I2O5 could be formed by a series of exothermic reactions involving the oxidation of I2O2, I2O3 and I2O4 by O3. In order to form pure I2O5 particles, modelling calculations indicate that the rate coefficients for these reactions probably need to be faster than 6 × 10−13 cm3 molecule−1 s−1 at 295 K. Applying this model to the atmosphere shows that ultra-fine iodine oxide particles formed in the coastal marine boundary layer would then consist of I2O5.

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