Part per hundred million

Parts per billion (ppb) Parts of a contaminant in a billion parts of air or water. Care has to be taken in ensuring the term billion is the correct one. In the past in the UK, a billion was 10 -, but in the U.S, a billion is 10 , It is now assumed that current practice relates to the latter. Other terms encountered are parts per hundred million (pphm) and parts per million (ppm). 

Toxicity and Hazards. The odor cf ozone can be detected in concn as low as several parts per hundred million by vol (pphm). The threshold limit value (TLV) is O.lppmor 0.2mg/m3 its toxic dose level (TDL), 50% kill concn is 2ppm (Ref 6) Pure 100% liq ozone may be kept safely at 90°K (cooled by liq oxygen) for indefinite periods of time, but the smallest provocation, such as a spark or fast warming, even only up to bp (161°K), causes detonation. The evapn of liq ozone, for example, in the process of the prepn of pure gaseous ozone is, therefore, a dangerous procedure (Ref 3, p 224)... 

Less than 1 pphm (parts per hundred million) of ozone in the atmosphere can severely attack non-resistant rubbers. However, there is far less, if any, problem with plastics and tests are rarely made. If required, the methods standardised for rubbers in ISO 1431 [24] could be used, which involve exposure in a special cabinet with controlled levels of ozone. 

Threshold concentrations for Ct+ alkenes are in the parts-per-hundred-million to parts-per-million range. Determination of their gas-phase concentration is required for assessing their contribution to atmospheric organic aerosol. 

For gas-phase species, the most commonly used units are parts per million (ppm), parts per hundred million (pphm), parts per billion (ppb), and parts per trillion (ppt). These units express the number of molecules of pollutant found in a million (10fi), a hundred million (10x), a billion (an American billion (109)), or a trillion (1012) molecules of air, respectively. It should be noted that, although these are commonly used, confusion may arise in that in some European countries a billion means 1012 and a trillion means 10l8. As a result, in some journals when these units are used, they are accompanied by a definition, e.g., ppb (parts in 109). Care must also be taken to ensure that ppt means parts per trillion and not parts per thousand. The latter unit is often used in isotope studies and is denoted parts per mille, or %o. 

The ozone concentration in the atmosphere is only a few pphm. In certain chemical plants as in electrolytic mercury cell houses in the chloralkali industry, the ozone concentration is higher. Although the atmospheric ozone level is low, it reacts with rubber double bonds rapidly and causes cracking of rubber products. Especially when rubber is under stress (stretching and bending as in the case of flexible cell covers), the crack development is faster. Neoprene products resist thousands of parts per hundred million of ozone for hours without surface cracking. This nature of neoprene is quite suitable for cell house application in chlor-alkali industries. Natural rubber will crack within minutes when subjected to ozone concentration of only 50 pphm. 

Ozone. 03 is the principal oxidizing component in photochemically produced air pollutants. Ozone probably causes more injury to vegetation than any other pollutant in the United States (6). Phytotoxic levels frequently occur near industrial complexes and densely populated urban areas. Exposure for two or more hours to concentrations of 10 parts per hundred million (pphm) of air may cause acute injury to several of the most sensitive species of plants. 

Sensitivity Studies on 1969 Trajectories with the Expanded Model. Based on the semi-Lagrangian formulation of the photochemical/diffusion model, the computed endpoint composition of the air masses depends on initial conditions, flux from the ground along the trajectories, and reaction rates. For our tests we concentrate on El Monte data because much of the polluted air there comes from somewhere else. This is believed to be a more severe test of the model than that at Huntington Park. The initial conditions are based on measurements insofar as possible. The principal initial values for the 1030 trajectory are as follows for 0730 PST (given in parts per hundred million) ... 

Atmospheric pollution cannot be controlled so long as the nature and the mechanism of formation of its deleterious constituents remain unknown. While many chemical constituents of polluted atmospheres have been identified, their presence or concentration does not seem to follow a regular pattern. On the other hand, ozone is always present in polluted outdoor atmospheres. Its concentration consistently rises from a normal value of a few parts per hundred million to many times this value during periods of severe contamination. Whether ozone is the primary cause of pollution or is a secondary effect of the reaction of other substances is not entirely clear, but it appears to be an important link in the chain of chemical reactions which produce atmospheric pollution. Very likely, a knowledge of the variations of ozone concentration in atmospheres would permit a study of the influence of the various parameters, and this knowledge may eventually furnish a lead to an explanation of the mechanism of formation and the effects of pollutants. 

Lyles, G. Dowling, F. Blanchard, V. "Quantitative Determination of Formaldehyde in the Parts Per Hundred Million Concentration Level" J. Air Pollution Control Association,... 

In the case of smaller concentrations pphm (parts per hundred million) and ppb (parts per billion where billion = I09) can also be used. Another possibility to express the atmospheric level of trace gases and aerosol particles is the mass concentration", which gives the mass of a substance per unit volume of air. The dimension of the mass concentration is g cm-3 or more frequently /ig m 3. This quantity is a function of the temperature and pressure since the air volume in the denominator depends upon these physical parameters. Thus, it is reasonable to express its values in /rg m 3 STP (standard temperature and pressure). In this book we will use concentrations expressed mainly in ppm and in ng m-3 STP. Table 4... 

The ozone concentration in the troposphere during the daytime is typically about 1 pphm (parts per hundred million parts of air by volume) [20], Values up to 100 pphm were measured in some photochemical smog areas. The molecular mechanism of the ozone aging of diene based elastomers was studied in detail and is well understood [19,21], Products or intermediates different from those arising in autoxidation or photo-oxidation of polymers were identified ozonides (3), zwitterions (4), diperoxides (5), polyperoxides (6), polymeric ozonides (7) and terminal aldehydes (8). Reactivity of aminic antiozonants (AOZ) with these species accounts for the protection of rubbers against atmospheric 03. AOZ must also possess antioxidant properties, because the free radical processes are concerted with ozonation due to the permanent presence of oxygen. 

As an example, we consider the fitting of a Weibull distribution to 1971 hourly average ozone data from Pasadena, California. The data consist of 8303 hourly values (there are 8760 h in a year). The maximum hourly value reported was 53 parts-per-hundred million (pphm). The arithmetic mean and standard deviation of the data are M = 4.0 pphm and M2 2 = 5.0 pphm, and the geometric mean and geometric standard deviation are 2.4 and 2.6 pphm, respectively. If one assumes that the hourly average ozone mixing ratios fit a Weibull distribution, the parameters of the distribution can be estimated from (26.51) and (26.52) to give X = 0.808 and a = 3.555 pphm. 

The notable exception is the exposure of rubber, including relex ant foams and coated fabrics, to ozone. Many rubbers are susceptable to cracking when exposed in the strained condition to ozone in very small quantities—this is in fact a case of environmental stress cracking discussed above for plastics. Ozone levels in the atmosphere arc generalK no more than the odd part per hundred million, but this is quite sufficient to cause severe damage. Accelerated tests are usually carried out in special ozone cabinets at levels between 25 and 200 parts per hundred million, and the procedures are described in Chapter 15. 

The rubber industry expresses ozone concentration as parts per hundred million parts of air. whereas environmental agencies have traditionally used parts per billion (thousand million). ASTM Dl 149 (the corresponding American test method to ISO 1431/1) expresses and specifies ozone concentration in terms of partial pressure to accommodate differences in barometric pressure between test laboratories. 50 mPa is equivalent to 50 pphm ozone... 

Specimens were exposed to an ozone concentration of 50+5 parts per hundred million at 4O+2°0 and relative humidity of 55+5%. During the ozone resistance tests, specimens were under a strain of 20+2%. 

Cut quartz crystals have characteristic modes of vibration that can be induced by painting electrodes on the opposite surfaces and applying a megaHertz ac voltage. The frequency is searched until the crystal goes into a resonance. The resonant frequency is very stable. It is a property of the material and maintains a value to a few parts per hundred million. When the surface is coated with a stiff mass, the frequency is altered. The shift in frequency is directly related to the surface mass for thin, stiff layers. The reaction of a substrate with this layer changes the constants of the film and further shifts the resonant frequency. These devices can be used in air, in vacuum, or in electrolyte solutions. 

Parts Per Hundred Million A relative unit of concentration, parts of one substance per 100 million parts of another. Parts can be measured by weight, volume, count, or any other suitable unit of measure. Used often to denote very small concentration of a substance, such as impurity or toxin, or in a medium, such as air. Also called pphm. 

The term antiozonant denotes any additive that protects rubber against ozone deterioration. Most frequently, the protective effect results from a reaction with ozone, in which case the term used is chemical antiozonant. Ozone is generated naturally by electrical discharge and also by solar radiation in the stratosphere. These sources produce ground-level ozone concentrations of 1-5 parts per hundred million (pphm). In urban environments, however, ozone reaches much higher levels, up to 25 (pphm) due to the ultraviolet photolysis of pollutants. Only a few parts per hundred million of ozone in air can cause rubber cracking, which may destroy the usefulness of elastomer products. Some desirable properties of an antiozonant additive are as follows ... 

Part per hundred million pphm 10-3/ 10- 7%o (or 7 ppt) relative to ocean water The mass fraction of impurity in the metal was less than 5 pphm... 

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