Submicron sulfate particles

Figure 1. An example of a time sequence of eddy flux measurements of submicron sulfate particles, obtained during a recent study over a deciduous forest at Oak Ridge, TN. Note that negative values indicate fluxes directed towards the ground, i.e., deposition.

One excellent example of a multiana-lytical laboratory study is the influence of submicron sized particles of ammonium sulfate ((NH4)2S04) on the atmospheric corrosion of selected metals [22]. These particles were aerosolized and deposited under dry conditions on the metal surface, whereby the deposited amounts corresponded to up to 10 years of exposure in indoor locations of USA. By introducing humidity into the exposure... 

The top-down approach involves size reduction by the application of three main types of force — compression, impact and shear. In the case of colloids, the small entities produced are subsequently kinetically stabilized against coalescence with the assistance of ingredients such as emulsifiers and stabilizers (Dickinson, 2003a). In this approach the ultimate particle size is dependent on factors such as the number of passes through the device (microfluidization), the time of emulsification (ultrasonics), the energy dissipation rate (homogenization pressure or shear-rate), the type and pore size of any membranes, the concentrations of emulsifiers and stabilizers, the dispersed phase volume fraction, the charge on the particles, and so on. To date, the top-down approach is the one that has been mainly involved in commercial scale production of nanomaterials. For example, the approach has been used to produce submicron liposomes for the delivery of ferrous sulfate, ascorbic acid, and other poorly absorbed hydrophilic compounds (Vuillemard, 1991 ... 

The tropospheric air always contains a considerable amount of small submicron particles, the so-called Aitken particles (AP), which are widely spread. Experimental data show that, on the average, not less than 50-75% of the total mass concentration of AP fall on sulfates [43]. The average percentage of the mass concentration of organic and nitrate components in the aerosol of the sub-micron range is estimated at 20-25% [2, 22]. Undoubtedly, nuclear explosions (with a yield of about 10 NO molecules per 1 Mt of trinitrotoluene equivalent [12] should generate great amounts of nitrate and sulfate aerosols, but there are no estimates so far. 

The hygroscopic properties of sulfate aerosols largely determine their specific weight. Depending on size, it varies from 1 to 2 g/cm . So, for instance, the mean bulk density of submicron particles substance is estimated in [41] at 1.37 g/cm and in [17] at (1.82-1.93) g/cm . 

Dimethylsulfoxide can readily be removed onto particles and there it can undergo an efficient oxidation through to methanesulfonate. This adds a significant pathway to the gas-phase production of methanesulfonic acid, which is present largely in the submicron aerosol fraction. Peak summer concentrations are 0.6 0.3 nmol m and at times this can amount to almost a quarter of the non-seasalt sulfate in the remote marine atmosphere (Jourdain and Legrand, 2001). 

What is the percentage of gas-to-particle sulfate formation in the very low submicron range ... 

This is in an unscrubbed plume. Now, concerning ammonia, you ae not really talking about ammonia as a catalyst for sulfate formation. The actual process is SO2 to sulfuric acid, followed by ammonia neutralization. The theory about SO2, water, ammonia catalysis is being questioned. The real process seems to be SO2 to sulfuric acid, then reaction with ammonia to form ammonium sulfate or ammonium bisulfate. In fact, in scavenging the sulfate, as the particle size increases, the scavenging efficiency also increases. Sulfuric acid aerosols are submicron particulates for which scavenging is very inefficient (Marsh, Atmos. Environ. 12 401-406, 1978). So what you are finding in a rain droplet is perhaps what is below the cloud or before the condensation nucleus stabilizes. 

More recently, ZnS-coated PS nanocomposite colloids were synthesized by the chemical bath deposition technique of thioacetamide in the presence of PS seed particles and metal salt [197], It allowed deposition of high refractive index ZnS shells of controlled thickness onto sulfate-modified and plain PS cores of size of about 200-500 nm. In order to prevent aggregations of PS particles, PVP was added during the reaction. The effective refractive index of the ZnS shell-PS core (PS/ZnS) composite particles varied between 1.73 and 1.98 at wavelengths above the optical absorption edge of ZnS. The porosity of the shells was between 12 and 19%, and the core-shell colloids served as building blocks for self-assembly at the submicron length scale [197]. 

In general, the levels of U.S. population exposure to acid aerosols are quite modest in comparison with the levels at which health effects have been demonstrated. The most likely acid sulfate species appears to be NH HSO particle sizes depend on the age of the aerosol but are in the submicron range. Elevated concentrations of acidity are likely to persist at a given location for a few days, at most. Gaseous acidity levels are likely to equal or exceed particulate acidity levels in most locations. 

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