Atmospheric particle levels

Nevertheless, considerable evidence snggests that particulate pollution contributes to exacerbations of asthma. Atmospheric particle levels have been linked with worsening of symptoms, decrements in limg function, increased hospital admissions for asthma, and increased medication use (31-33). Recent clinical studies demonstrate that exposure to ozone increases airway inflammation in patients with mild asthma (34,35). Whether exposure to ambient particles also exacerbates airway inflammation in asthma has not been demonstrated. However, two recent studies suggest that exposure to acid aerosols either followed by (36), or in combination with (37), ozone exposure may increase airway responsiveness to ozone in subjects with asthma, at concentrations of acid aerosol well below those known to cause changes in lung function or airway inflammation in the absence of ozone (38). 

Given the complexity of particle size distributions in the atmosphere (see Chapter 9.A), as well as the large number of chemical components (Chapter 9.C) that are not distributed equally throughout the various sizes, characterizing a typical collection of particles in the atmosphere is not possible. However, some indication of particle levels in the atmosphere is provided by mass measurements of PMm (i.e., total mass less than 10 gm in diameter), for which extensive measurements have been made for regulatory purposes. 

The exchange of chemical compounds from the gas phase to a surface, e.g. atmospheric particles, soil, water, vegetation or other surfaces, is controlled by the affinity of the compound to this surface. The ratio of vapour pressure to water solubility can be used as indicator between levels in the atmosphere and water surface (Henry s law H constant). In many model calculations, the ratio between POP levels in octanol and water, the octanol-water partitioning coefficient (Kow), is used as reference for the distribution of POP in organic material [14]. Consequently, the expression ///RT (Cair/Cwalcr) and Kow (Coctanoi/Cwater) provide the octanol-air partitioning coefficient (Koa) ... 

The size distribution of air particles not only influences the distribution and partitioning dynamics of POPs, but also determines dry and wet deposition flux of POPs. An interesting phenomenon was observed for relationship among atmospheric PAHs, particle size distribution, and the levels of PAHs in soil (Kim, 2004). For urban sites, the composition pattern and absolute concentrations of PAHs in soil were well correlated with those in air where the atmospheric particles size was distributed evenly among seasons with predominant amount of fine particles < 3 pm. Dry deposition flux of PAHs followed seasonal variation in atmospheric concentration in urban site. However, at a suburban site with large seasonal variation in particle size distribution, dry deposition flux and soil residue did not reflect the seasonal variation of atmospheric PAHs. From this result, site-specificity in atmospheric particle distribution may also influence the distribution and residues in the underlying soil. 

The corrections made by van der Waals to the kinetic molecular theory make physical sense, which makes us confident that we understand the fundamentals of gas behavior at the particle level. This is significant because so much important chemistry takes place in the gas phase. In fact, the mixture of gases called the atmosphere is vital to our existence. In the next section we consider some of the important reactions that occur in the atmosphere. 

Despite the clear evidence of a subpopulation of individuals sensitive to near-ambient peak levels of sulfur dioxide, the two-decade-old NAAQS for sulfur dioxide has not been changed nor has a short-term peak standard been instituted. A considerably greater amount of attention has been placed on the contribution of airborne particulates, particularly those associated with sulfur oxides, to adverse health effects. The carbon-, mineral-, and heavy metal-based particles produced during fossil fuel combustion and smelting promote the conversion of sulfur dioxide to sulfuric acid. Recognition of sulfur dioxide-particle interactions comes as a result of findings garnered from a number of animal studies and the characterization of sulfuric acid, ammonium sulfate, and ammonium bisulfate associated with atmospheric particles. The importance of the coexistence of sulfur oxides and particulate matter is reflected in the... 

Wood combustion has been identified as a source that can contribute significantly to atmospheric particulate levels (Core et al. 1984 Ramdahl et al. 1984b Sexton et al. 1984 Standley and Simoneit 1987 Hawthorne et al. 1992). Fine-particle emission rates reported by Hildemann et al. (1991a) are shown in Table 14.7. 

Polychlorinated biphenyls (PCBs 13) as well as DDT (14) and related compounds have been detected in air and atmospheric particle samples (Harvey and Steinhauer, 1974 Bidleman and Olney, 1974). Indoor air may contain rather high levels of... 

The distribution of chemical between environmental phases is at the core of understanding enviromnental fate. Examples of environmental phase distribntions are those between air and water, between atmospheric particles and the gas phase, between plants and air, between soil and air, between suspended matter and the dissolved phase in water, and between groundwater and snbsnrface solids. On a fundamental level, the distribntion behavior of a chemical determines where a chemical is residing in the environment. It further influences the natnre and extent of the transport and transformation processes it will experience. The distribution of a chemical between gas phase and particle phase in the atmosphere not only determines by which mechanism and how fast the chemical is being deposited to the Earth s sitrface, bnt also further determines the type and rate of reactions that it will experience in the atmosphere. A chemical in a water body experiences very different behavior depending on whether it is dissolved in water or whether it sorbs to colloidal or sohd matter suspended in the water colimm. Similarly, the mobility and reactivity of a contaminant in the snbsnrface enviromnent depend strongly on its distribution between water and solids. 

Colloidal-sized atmospheric particle Famed by condensation of vapors or reactions of gases Famed by grinding of solids, atomization of liquids, or dispersion of dust Tam denoting a high level of water droplets Denotes decreased visibility due to the presence of particles Liquid particles... 

Ohura, T. Fujima, S. Amagai, T. Shinomiya, M. (2008) Chlorinated Polycyclic Aromatic Hydrocarbons in the Atmosphere Seasonal Levels, Gas-Particle Partitioning, and Origin. Environ. Sci. Technol. 42, 3296-3302. 

Gas-phase reactions play a fundamental role in nature, for example atmospheric chemistry [1, 2, 3, 4 and 5] and interstellar chemistry [6], as well as in many teclmical processes, for example combustion and exliaust fiime cleansing [7, 8 and 9], Apart from such practical aspects the study of gas-phase reactions has provided the basis for our understanding of chemical reaction mechanisms on a microscopic level. The typically small particle densities in the gas phase mean that reactions occur in well defined elementary steps, usually not involving more than three particles. 

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