Ambient particle concentration

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. 

III. Studying Ambient Particles Using an Ambient Particle Concentrator... 

Figure 3 Schematic diagram of the ambient particle concentrating system used to conduct animal exposures. The RH/T probe measures relative humidity and temperature. Specific honeycomb denuders can be used to remove varying gaseous aerosol components (14,15). (From Ref 14.)...

Zone I combustion proceeds at an overall rate equal to the product of the intrinsic burning rate, evaluated at the ambient oxygen concentration, and the total internal surface area. The char diameter necessarily stays constant and the particle density continually decreases as particle mass is evenly removed throughout the particle on the pore surfaces (constant-diameter combustion). 

The basic assumption of these receptor models is that the ambient airborne particle concentrations measured at a receptor can be apportioned between several sources. In other words, each chemical element concentration at the receptor is considered as a linear combination of the mass fraction of the source contributions. 

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... 

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. 

Urban aerosols are complicated systems composed of material from many different sources. Achieving cost-effective air particle reductions in airsheds not meeting national ambient air quality standards requires identification of major aerosol sources and quantitative determination of their contribution to particle concentrations. Quantitative source Impact assesment, however, requires either calculation of a source s impact from fundamental meteorological principles using source oriented dispersion models, or resolving source contributions with receptor models based on the measurement of characteristic chemical and physical aerosol features. Q)... 

Ambient aerosols, particularly those with diameters less than 3pm, are a serious pollution problem. Carbonaceous material is a major component of the fine particle concentration (10 and has undergone extensive study in the past few years (, ) in large part because of the concern that these particles play an Important role in urban haze and community health. 

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 10.22 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). 

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. 

Wildfires represent a major source of atmospheric particulate matter (PM) especially fine particles with diameter <2.5 pm (PM2.5). High ambient fine particle concentrations are associated with serious health problems [4], At times extensive... 

Fine particulate matter (PM) is well known to cause serious negative impacts on human health [1-4], As a consequence, ambient PM concentrations are regulated in many countries worldwide. For example, air quality standards for the mass concentration of particles with aerodynamic diameter less than 10 pm (PM10) are in the European Union set to 40 pg/m3 (annual mean) and 50 pg/m3 (daily mean). In the USA, the daily limit value forPMlOis 150 pg/m3 in addition, the mass concentration of the finer fraction of particulate matter PM2.5 is not allowed to exceed 35 pg/m3 (annual mean) and 15 pg/m3 (daily mean), respectively. The World Health Organization (WHO) has set air quality guideline values for the annual mean and daily mean concentrations of ambient PM10 (PM2.5) at 20 pg/m3 (10 pg/m3) and 40 pg/m3 (20 pg/m3), respectively [5]. 

The magnitude of aerosol generation is sufficient to make these reactions of interest in regard to human health. A large body of epidemiological literature indicates that increases in ambient aerosol concentrations are associated with increased mortality. In particular, an increase of 25pgm"3 in particle mass concentration for PM2.5 (total particle mass for particles with an aerodynamic... 

Sulfate particle concentrations average 8-10 /xg/m3 annually in the Eastern U.S. it is rare for short term (3-24 hour) levels to exceed about 50 /xg/m3. There are no Federal ambient standards for sulfate particles. 

Public concern for the hazards of particle suspensions in the indoor and outdoor environment has produced regulations limiting particle concentrations and exposure levels. In the workplace, dust hazards are constrained by total mass concentration as well as concentration of specific toxic chemicals. In the ambient air, protection is stipulated in terms of total mass concentration of suspended particles andcertain chemical species, namely, lead and sulfate. Recently, measures of exposure have begun to distinguish between fine particles less than 2.5 fxm and coarse particles between 2.5 and 10 fxm. This separation relates to the ability of particles to penetrate the human respiratory system, and to different sources of fine and coarse particles. 

---