Coarse particles atmosphere

Zhuang, H., C. K. Chan, M. Fang, and A. S. Wexler (1999) Formation of nitrate and non-seasalt sulfate on coarse particles. Atmospheric Environment 33, 4223-4233... 

The StabUity or persistence of a poUutant in the atmosphere depends on the poUutant s atmospheric residence time. Mean residence times and principal atmospheric sinks for a variety of species are given in Table 2. Species like SO2, (NO and NO2), and coarse particles have lifetimes less than... 

Impurities in mineral fillers can have serious effects. Coarse particles (grit) will lead to points of weakness in soft polymers which will therefore fail under stresses below that which might be expected. Traces of copper, manganese and iron can affect the oxidative stability whilst lead may react with sulphur-containing additives or sulphurous fumes in the atmosphere to give a discoloured product. 

Airborne particulate matter, which includes dust, dirt, soot, smoke, and liquid droplets emitted into the air, is small enough to be suspended in the atmosphere. Airborne particulate matter may be a complex mixture of organic and inorganic substances. They can be characterized by their physical attributes, which influence their transport and deposition, and their chemical composition, which influences their effect on health. The physical attributes of airborne particulates include mass concentration and size distribution. Ambient levels of mass concentration are measured in micrograms per cubic meter (mg/m ) size attributes are usually measured in aerodynamic diameter. Particulate matter (PM) exceeding 2.5 microns (/i) in aerodynamic diameter is generally defined as coarse particles, while particles smaller than 2.5 mm (PMj,) are called fine particles. 

Studies of atmospheric particles show that their distribution is often birno-dal i.e., the particles are made up of rwo separate fractions, one with fine and one with coarse particles (Fig. 9.1). The coarse particles, from about 2.5 pm upward, are made up of natural dust from the effect of wind, erosion, plants, volcanoes, etc. The finer fraction is made up of particles smaller than 2.5 pm and consists primarily of particles from human activity, combustion, traffic, and processes. 

The atmospheric aerosols were filtered by a two-stage sampler that classified them into fine (< 1.2 pm) and coarse (> 1.2 pm) fractions, which were then further classified into 13 size ranges between 0.01 to 30 pm. An example of a PIXE spectrum of a coarse particle is illustrated in Figure 4.21. 

To find answers to these crucial questions and to establish if the occurrence of psychotropic substances in the atmospheric aerosols is just a curiosity or rather a potential problem for the community, a series of investigations have been carried out both in the laboratory and in the field. Dedicated procedures have been optimised, for instance, for cocaine and cannabinoids (see sections below), and the chemical stability of cocaine in airborne particulates and its partition between gas and aerosol phases were estimated, as well as its accumulation in fine rather than coarse particles. Furthermore, cocaine and cannabinoids concentrations have been measured in several cities over the world through field studies. After the first detection of cocaine in ambient air by Hannigan et al. [1] in Los Angeles, measurements were performed more extensively in Italy (for instance over 10 consecutive months in downtown Rome, or in 38 Italian localities) and Spain... 

The average particle size distributions for four predominantly crustal elements, Al, Si, Ca, and Ti, are shown in Figure 3. They are essentially identical. It should be pointed out that the downturn of the relative concentrations above 8 ymad (impactor stage 6) is the combined result of the actual distribution of particle sizes in the atmosphere and the efficiency with which these very coarse particles can enter (upward) into the cascade impactor. This efficiency must decrease with increasing particle size and generally depend on inlet design and wind speed. Nevertheless, it is important to note here that the patterns of the four elements are similar, implying a common aerosol source. 

Indeed, based on the number, surface, and volume distributions shown in Fig. 9.6, Whitby and co-workers suggested that there were three distinct groups of particles contributing to this atmospheric aerosol. Particles with diameters >2.5 yu,m are identified as coarse particles and those with diameters 2.5 pm are called fine particles. The fine particle mode typically includes most of the total number of particles and a large fraction of the mass, for example, about one-third of the mass in nonurban areas and about one-half in urban areas. The fine particle mode can be further broken down into particles with diameters between 0.08 and 1-2 yxm, known as the accumulation range, and those with diam-... 

Particles in the accumulation range tend to represent only a small portion of the total particle number (e.g., 5%) but a significant portion (e.g., 50%) of the aerosol mass. Because they are too small to settle out rapidly (see later), they are removed by incorporation into cloud droplets followed by rainout, or by washout during precipitation. Alternatively, they may be carried to surfaces by eddy diffusion and advection and undergo dry deposition. As a result, they have much longer lifetimes than coarse particles. This long lifetime, combined with their effects on visibility, cloud formation, and health, makes them of great importance in atmospheric chemistry. 

Harrison J, Yin J, Mark D, Stedman J, Appleby RS, Booker J, Moorcroft S (2001) Studies of the coarse particle (2.5-10um) component in UK urban atmospheres. Atmos Environ 35 3667-3679... 

Carbonaceous aerosols in the atmosphere are complex in nature and are found in both coarse particles (> about 2.5 pm) and fine particles (< about 2.5 pm). Sources of carbon-containing particles are varied and include resuspended soil particles, pollen, plant waxes, etc. in the coarse fraction, and soot particles, sorbed organics including PAHs, and secondary aerosols resulting from... 

The stability or persistence of a pollutant in the atmosphere depends on the pollutant s atmospheric residence time. Mean residence times and principal atmospheric sinks for a variety of species are given in Table 2. Species like S02, NO (NO and N02), and coarse particles have lifetimes less than a day thus important environmental impacts from these as primary pollutants are usually within close proximity to the emissions sources. In the presence of high concentrations of NO, the residence time of 03 is on the order of seconds to hours. In the relatively nonpolluted environment of the free troposphere, from approximately 1500 m to the top of the troposphere ( 12 km), the 90-day lifetime applies. Consequently, given the right conditions, 03 could have important environmental impact far downwind from its source. In fact, concentrations of 03 near the NAAQS limit have been transported from the Gulf Coast of the United States to the Northeast over a several-day period (9). 

Sulfate is the ultimate product of the oxidation of SO2. We might expect small concentrations of other species, such as dithionates that are intermediates in the oxidation process, although these have not been detected. Concentrations of sulfate particles in the remote atmosphere are typically at a few nanomoles per cubic meter. In the marine atmosphere the sulfate is found both in coarse particles where it derives from seasalt and in fine particles around a micron in diameter as... 

The different size modes reflect differences in particle sources, transformations, and sinks (Finlayson-Pitts and Pitts 2000). For example, coarse particles are generated by mechanical processes such as wind erosion of soil, wave action in the oceans, and abrasion of plant material. In contrast, many of the fine particles in the atmosphere are produced from either primary emissions from combustion sources or via atmospheric gas-to-particle conversions (i.e., new particle formation). The relative and absolute sizes of particle modes, as well as the number of modes, can vary greatly in different locations and at different times. In addition, the chemical composition of particles within one size... 

Several authors confirm that elements related to anthropogenic activities, are concentrated into very small size particles, with a mean aerodynamic diameter less than 2 pm, in the atmosphere. At the same time heavy metals, whose emissions in the atmosphere are related to natural sources, are concentrated into coarse particles with a mean aerodynamic diameter greater than 2 pm (4-10). 

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