Urban aerosol particle concentrations

From the fonn of Equation 6.6 it is clear that will be low for chemicals that have ATpA lower than Va/Vp, which has a typical value of about 2 x 10. Benzene, HCB, and Lindane all have very low ( ) and can be expected to be found predominantly in the gas phase under most environmental conditions. B(a)P is estimated to be 4% on particles under this generic scenario, and 4) may be considerably higher at low temperatures, or when aerosol particle concentrations are higher, for example in an urban area. Nickel can be expected to be 100% particle-associated in the atmosphere under all conditions. 

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. 

Notholt et al. (1992) and Andres-Hernandez et al. (1996) measured HONO, NO, N02, and aerosol surface areas at both urban and nonurban locations. They observed that at Ispra, Italy, HONO concentrations tended to correlate with N02, NO, and aerosol surface areas. Such studies support the formation of HONO from heterogeneous reactions of N02 at the surfaces of aerosol particles, fogs, buildings, and the ground. 

Vakeva M, Hameri K, Kulmala M, Lahdes R, Ruuskanen J, Laitinen T (1999) Street level versus rooftop concentrations of submicron aerosol particles and gaseous pollutants in an urban street canyon. Atmos Environ 33 1385-1397... 

Example 16.3 A typical urban aerosol has an average particle concentration of 75 pgfrn3. Assuming that the average particle can be represented by a 0.6-(xm sphere with a density of 2 g/cm3, determine the value of y, in 1/meters, if... 

An example of the information obtainable from measurements of aerosol particle composition as a function of size is given in Figure 10. In this study of the evolution of aerosol composition in an urban air-shed, a multi-stage impactor was used to separate particles by size for the determination of size-dependent composition. The particle mass concentration increases as air moves inland from Santa Catalina Island to Long Beach, Fullerton, and finally Riverside, as do substances such as nitrate. Differences in particle composition as a function of size at a given site and from site to site are evident. 

Shi JP, Khan A A, Harrison RM (1999) Measurements of ultrafine particle concentration and size distribution in the urban atmosphere. Sci Total Environ 235 51-64 Siefert RL, Pehkonen SO, Erel Y, Hoffmatm MR (1994) Iron photochemistry of aqueous suspensions of ambient aerosol with added organic-acids. Geochim Cosmochim Acta 58 3271-3279 Sievering H, Boatman J, Gorman E, Kim Y, Anderson L, Ennis G, Luria M, Pandis S (1992) Removal of sulphur from the marine boimdaiy layer by ozone oxidation in sea-salt aerosols. Nature 360 571-573 Siffert C, Sulzberger B (1991) Light-induced dissolution of hematite in the presence of oxalate-A case-study. Langmuir 7 1627-1634... 

Number size distribution of aerosol particles under urban conditions according to Whitby (1978). N number of particles tln diameter of particles FT total volume concentration r. correlation coefficient between power law given in the figure and experimental data. (By courtesy of Atmospheric Environment)... 

Table VI summarizes aerosol mass concentrations and composition in different regions of the troposphere. It is interesting to note that average total fine particle mass (that associated with particles of diameter less than about 2 /im) in non-urban continental, i.e., regional, aerosols is only a factor of two lower than urban values. This reflects the relatively long residence time of particles (recall the estimate of a lifetime of fine particles by dry deposition of 10 days). Correspondingly, the average composition of non-urban continental and urban aerosols is roughly the same. The average mass concentration of remote aerosols is a factor of three lower than that of non-urban continental aerosols. The elemental carbon component, a direct indicator of anthropogenic combustion sources, drops to 0.3% in the remote aerosols, but sulfate is still a major compo-...

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