Ambient particles

Particles in the atmosphere come from different sources, e.g., combustion, windblown dust, and gas-to-particle conversion processes (see Chapter 6). Figure 2-2 illustrates the wide range of particle diameters potentially present in the ambient atmosphere. A typical size distribution of ambient particles is shown in Fig. 2-3. The distribution of number, surface, and mass can occur over different diameters for the same aerosol. Variation in chemical composition as a function of particle diameter has also been observed, as shown in Table 4-3. 

Vcdal S. (1997). Ambient particles and health lines that divide. /., 4ir and Waste. Manage.. 4.ssoc. 47,. 551-581,... 

Zielinska B, J Arey, R Atkinson, PA McElroy (1988) Nitration of acephenanthrylene under simulated atmospheric conditions and in solution and the presence of nitroacephenanthrylenes in ambient particles. Environ Sci Technol 22 1044-1048. 

It is important to update the bronchial dosimetry for radon daughters as new information becomes available. It is the purpose of this study to show that there is a potential for either significantly increased bronchial dose in the home per unit exposure if the ambient particle size is artificially reduced due, for example, to open-flame burning or use of kerosene heaters, or a decreased dose if hygroscopic particles dominate the indoor aerosol. 

This 10-year longitudinal study is focused on the potential associations between ambient air pollution and respiratory health in children. The objectives are to document the respiratory growth of study participants, to assess whether ambient pollutants play a role in respiratory health, and to identify which pollutants are responsible for any observed effects. Ambient air quality is being monitored in each of twelve communities by centrally located regional stations, CA, which also collect standard meteorological data. Gaseous pollutants are monitored continuously, while ambient particle concentration and size are determined by a number of approaches. Additional exposure assessment occurs because of the establishment of the Particle Center, including more extensive particle size number, surface area, and volume distribution measurements. 

In view of our knowledge of the composition of particles from most sources In the Washington area. It Is appropriate to use the CEB method rather than methods that extract source compositions from data on ambient particles. According to the CEB method, the concentration of an element 1 In a receptor sample Is given by... 

Coal-fired power plants release very large amounts of particulate material. The question Is, however, what fractions of the various elements In ambient air can be accounted for by particles from coal-fired plants A major fraction of an element can be contributed by coal combustion only If (1) coal accounts for an appreciable fraction of the A1 In the local atmosphere and (2) the EF value of the element on particles from coal combustion Is as great as for ambient particles. Only for those elements In Figure 1 for which there Is considerable overlap between the ranges for cities and for coal-fired plants can coal possibly be a major contributor. Even If there Is overlap, coal Is not necessarily a major source, as condition 1 above may not be met. On this basis, coal combustion could be a major source of many llthophlles plus Cr, N1, As, Se and, In cities where little residual oil Is used (Charleston and St. Louis), V. The very high EF values for As and Se and low values for V and Nl In Charleston, where little oil and a great deal of coal are burned, lends credence to this Interpretation. 

The enormous enrichments of Se on ambient particles relative to particles from coal-fired plants are surely due to the same problems as noted for As, but especially the well established fact that a major fraction of Se Is In the vapor phase at stack temperatures (47, 48). The very large Se enrichments for ambient particles Indicate that much of the vapor-phase Se condenses on particles after release. In some areas there may be additional Important sources of As and Se, e.g., non-ferrous smelters. 

One particular type of source that should be studied carefully Is entrained soil. As shown above, this Is often the greatest contributor of TSP In urban areas. As there Is so much of It present, we need to know concentrations of all measured elements quite well to make an accurate determination of the residual amounts left to be accounted for by other sources. The composition of selved soil Is often used for the soil component, but there may be considerable fractionation Imposed by entrainment, e.g., preferential selection of very fine clay mineral particles. Such fractionation has been demonstrated In the very limited studies of entrainment of particles from soil of known composition (e.g.. Refs. 21, 49). These studies can probably best be done In controlled environments such as wind tunnels. One cannot simply collect ambient particles In the countryside and consider it to be soil, as there are anthropogenic contributions even at great distances from cities ( ). There Is further confusion betwen clean, "continental" dust and "urban" dust. The latter, which Is usually collected near city streets (21, 50), typically has a composition of soil contaminated by anthropogenic emissions, especially from motor vehicles. 

Vedal, S., Ambient Particles and Health Lines That Divide, J. Air Waste Manage. Assoc., 47, 551-581 (1997). 

TABLE 9.18 Some Difunctionally Substituted Alkane Derivatives Found in Submicron Ambient Particles in Urban Air ... 

Concurrently, Gordon and co-workers (1973) reported another important phenomenon benzene extracts of airborne particles collected in the Los Angeles Air Basin had 100-1000 times the cell transformation activity of that which could be attributed to the measured levels of known PAHs in the samples. Strikingly, the polar (methanol) fraction of these extracts, which amounted to only 3% of the total mass in the sample of ambient particles, had an activity equal to the neutral benzene extract that contained the remaining 97% of the PAHs (including BaP). 

Another powerful direct mutagen identified in ambient particulate matter collected in Santiago, Chile, is 3,6-dinitrobenzo[a]pyrene. Although its concentration is low (0.002 ng m-3 of air), its specific direct activities on strains TA98 and YG1024 ( —S9 mix) are high, 400,000 and 4,800,00 rev /rg-1, respectively (Sera et al, 1991). For a discussion of polar forms of BaP in ambient particles, see Ismail et al. (1998). 

FIGURE 10.18 Seasonal variation in the mutagen density (rev m-3, TA98, —S9) of extracts of ambient particles, and the associated BaP levels (ng m 3), collected at four sites in Athens, Greece, February 1984-January 1985. The annual average was 1.9 rev m-3 (adapted from Viras et al., 1990). 

TABLE 10.22 Average ( +S9 and — S9) and Highest (— S9) Values of Mutagenicityb (rev m 3) of Ambient Particles Collected1 at Seven Cities/ Sites in California 1 with Different Types of Emission Sources"... 

FIGURE 10.22 Direct mutagenicity of ambient particles (mutagen density, rev m-3, TA98, —S9) as a function of ambient concentrations of 2-nitropyrene, a directly mutagenic product of a gas-phase atmospheric reaction initiated by OH radical attack on pyrene. Samples collected at six sites in California with different types of emissions ( ) Glendora (O) Yuba City ( ) Concord ( ) Mammoth Lakes ( a ) Oildale ( ) Reseda (see Fig. 10.22) (adapted from Atkinson et al., 1988a). 

Assay) 1 of Fine Ambient Particles Collected at Upwind Background (San Nicolas Island), Urban (Long Beach and Central Los Angeles), and Downwind (Azusa and Rubidoux) Sites across Southern Californiaa c,d... 

In one of the first studies of the vapor-phase mutagenicity of polluted urban air, Alfheim and co-workers (1985) collected both ambient particles and vapor-phase compounds and used the Salmonella typhlmurium reversion assay. The direct activities ( —S9) of the extracts generally exceeded the promutagenicities (+ S9), and furthermore, the vapor-phase mutagenicity ranged from 0 to 88% of the total activity. 

Based in part upon this pioneering research, a National Academy of Sciences Committee suggested in their 1972 document Particulate Polycyclic Organic Matter that photolysis, photooxidations, and gas-particle interactions might lead to significant degradation of PAHs in ambient particles and formation of products more polar than the parent PAHs (NRC, 1972). 

Such a surface/bulk reactivity phenomenon may in part be responsible for the low (or zero) reactivity reported for BaP deposited on, or present in, a variety of substrates and exposed to ambient levels of 03 (e.g., 100 ppb) in air (see Grosjean et al., 1983 and Coutant et al., 1988). These observations can be rationalized by assuming that, while BaP in fact does react rapidly with 03 in ambient particles, not all of it is at (or close enough to) the surface to be available for reaction (Atkinson et al., 1988a Arey, 1998a). 

Pitts et al. (1986) exposed five individual PAHs, pyrene, fluoranthene, benz[a]anthracene, BeP, and BaP, deposited on glass fiber and Teflon-impregnated glass fiber filter (TIGF) substrates passively for 3 h in the dark in a 360-L Teflon environmental chamber to 50-300 ppb of 03 in air at several relative humidities. These experimental conditions more nearly resemble the actual exposure of ambient particles to 03 (in the dark) during transport than do exposures in Hi-Vol flow systems. Consistent with earlier studies, BaP, BaA,... 

Fresh ambient particulate POM sampled near a freeway was also exposed in this passive system for 3 h in the dark to 200 ppb of 03 in air at 1% RH. Concentrations of specific PAHs determined in the ambient particles and their percent reacted were similar for samples collected on both kinds of filters (glass fiber and TIGF). Again, under passive exposure conditions to approximately ambient levels of 03, BaP and BaA were found to be significantly more reactive than BeP. 

For example, Legzdins and co-workers (1994) used the bioassay-directed fractionation and chemical analysis technique to isolate, identify, and quantify 2-nitrofluoranthene in extracts of ambient particles collected in Hamilton, Ontario, Canada. They found it accounted for 70% of the total nonpolar direct bacterial mutagenicity (strain YG1021, standard reversion assay, Maron and Ames, 1983). 

Additionally, in two different monitoring campaigns conducted in the center of Milan, Italy, Ciccioli and co-workers (1993) reported 2-nitrofluoranthene, 2-nitropyrene, and 1-nitropyrene were the only ni-troarenes detected. Subsequently, in a comprehensive study of the atmospheric formation and transport of 2-nitrofluoranthene and 2-nitropyrene, they established their presence and levels in ambient particles collected at sites located in urban, suburban, forest, and remote areas in Europe, Asia, America, and Antarctica (Ciccioli et al., 1996, and references therein see also Ciccioli et al., 1995). 

As an example of typical experimental data, Fig. 10.32 is a GC-MS selected ion monitoring (SIM) profile (m/z 247) for the nitrofluoranthenes and nitropy-renes in an extract of ambient particles collected in southern California (Arey et al., 1988b). The 1-nitropyrene (1-NP) and 3-nitrofluoranthene (3-NF) presumably are from diesel emissions (Tables 10.33 and 10.34), but the dominance of 2-nitrofluoranthene and 2-nitropyrene reflects a second major source. 

FIGURE 10.32 GC-MS selected ion monitoring (SIM) scan of the molecular ions (m/z 247) of nitrofluoranthene (NF) and nitropy-rene (NP) isomers in extracts of ambient particles collected in Torrance, California, January 1986 (adapted from Arey et at., 1988b, and Atkinson and Arey, 1997). 

Figure 10.35 is the GC-MS m/z 247 profile of the nitrofluoranthenes and nitropyrenes in an extract of an ambient particle sample collected at night (Arey et al., 1988b). The high ratio of 2-nitrofluoranthene to 2-nit-ropyrene observed in this nighttime sample is indicative of nighttime gas-phase NO, radical reactions (for a review, see Kwok et al., 1994b). An NO, radical initiated mechanism for atmospheric formation of 2-nitrofluoranthene is shown in Fig. 10.36 (Atkinson and Arey, 1997 Arey, 1998a, and references therein). Analogous to the OH reaction, NO, is proposed to add to the ring to form a fluoranthene-NO, adduct, followed by ortho addition of N02 and subsequent loss of HNO,. This reaction is noteworthy because of its selectivity i.e., only 2-nitrofluoranthene is formed, and in high yield (24%) compared to the OH-initiated daytime reaction (3%).

Zielinska, B., J. Arey, R. Atkinson, and P. A. McElroy, Nitration of Acephenanthrylene under Simulated Atmospheric Conditions and in Solution and the Presence of Nitroacephenanthrylene(s) in Ambient Particles, Environ. Sci. Technol., 22, 1044-1048 (1988a). 

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