Aerosol property measurements

Ambient aerosol property measurements are quite sophisticated source measurements are not as well developed. Certain aerosol property measurements have been made on emissions of many sources. Unfortunately these tests seldom provide a full accounting of samples, sometimes do not report confidence Intervals on the measurements, and often do not fully describe the operating parameters of the source at the time of the test. 

TABLE 14.8 Some Cloud and Subcloud Aerosol Properties Measured in Polluted and Clean Air Masses near the Azoresu... 

Hand J. 2002. Comparisons of aerosol properties measured by impactors and light scattering from individual particles Refractive index, number and volume concentrations, and size distributions. Atmos. Environ. 36 1853-1861. 

Hildemann, L. M., Cass, G. R., Mazurek, M. A., and Simoneit, B. R. T. (1993) Mathematical modeling of urban organic aerosols properties measured by high-resolution gas chromatography. Environ. Sci. TechnoL, 27, 2045-2055. 

The future development of the chemical mass balance receptor model should include 1) more chemical components measured in different size ranges at both source and receptor 2) study of other mathematical methods of solving the chemical mass balance equations 3) validated and documented computer routines for calculations and error estimates and 4) extension of the chemical mass balance to an "aerosol properties balance" to apportion other aerosol indices such as light extinction. 

The microscopic receptor model can include many more aerosol properties than have been used in the chemical mass balance and multivariate models. The data inputs required for this model are the ambient properties measurements and the source properties measurements. To estimate the confidence Interval of the calculated source contributions the uncertainties of the source and receptor measurements are also required. Microscopists generally agree that a list of likely source contributors, their location with respect to the receptor, and windflow during sampling are helpful in confirming their source assignments. 

Existing data on characteristics of particles from various types of sources are inadequate for general use, though they have been used in specific studies with some success. Most of the source tests have been made for purposes other than receptor modeling and complete chemical and microscopical analyses have not been performed. Source operating parameters which might affect the aerosol properties of emissions have not been identified nor measured in ambient sampling and no provision is made for likely transformations of the source material when it comes into equilibrium under ambient conditions. 

Hegg, D. A., P. V. Hobbs, R. J. Ferek, and A. P. Waggoner, Measurements of Some Aerosol Properties Relevant to Radiative Forcing on the East Coast of the United States, J. Appl. Meteorol., 34, 2306-2315 (1995). 

Torres, 0 P. K. Bhartia, J. R. Herman, Z. Ahmad, and J. Gleason, Derivation of Aerosol Properties from Satellite Measurements of Backscattered Ultraviolet Radiation Theoretical Basis, J. Geophys. Res., 103, 17099-17110(1998). 

Linear polarization ratios have also been measured remotely. For example, results are given by Ward et al. (1973) and by Reagan et al. (1980). The sensitivity of scattering diagrams (Fig. 13.8), especially polarization (Fig. 13.9), to particle shape signals caution in inferring aerosol properties such as k from bistatic remote sensing. 

Size-resolved chemical information is much more difficult to obtain. The many applications of the differential mobility analyzer in measuring properties of size-classified particles are important tools for the characterization of aerosol systems, but the approaches demonstrated to date yield limited data. Vapor pressures, surface tension, and optical absorption have been measured on mobility-classified aerosols. Direct measurements of the distribution of chemical composition with particle size are needed. Elemental... 

Torres, O., Bhartia, P.K., Herman, J.R., Ahmad, Z and Gleason, J. (1998) Derivation of aerosol properties from satellite measurements of backscattered ultraviolet radiation Theoretical basis, J. Geophys. Res., 103, pp. 17,099-17,110. 

Toledano C, Cachorro VE, Gausa M, Stebel K, Aaltonen V, Berjon A, Ortiz de Galisteo JP, de Frutos AM, Bennouna Y, Blindheim S, Myhre CL, Zibordi G, Wehrli C, Kratzer S, Hakansson B, Carlund T, de Leeuw G, Herber A, Torres B (2012) Overview of sun photometer measurements of aerosol properties in Scandinavia and Svalbard. Atmos Environ 52 18-28... 

Several European intensive short-term ( campaign-type ) projects have provided important information on the atmospheric aerosol properties in Europe, usually by concentrating on specific aerosol properties or interactions. However, these kinds of campaign-type measurements do not necessarily represent the seasonal or annual variations of the aerosol concentrations and can overestimate some properties of the aerosol populations. Long-term measurements, especially with intercalibrated instruments and common data handling and calibration protocols make the data comparison between stations much more reliable and provide the end users (e.g., atmospheric modelers) good datasets to compare with. 

GUAN is a network of multiple German institutes with an interest in submicron aerosol properties, which was established in 2008 [17]. The methodologies of particle number size distribution measurements and data handling procedures in both GUAN and EUSAAR networks are very similar, and the size distribution measurement results are comparable between the two networks. The EUSAAR measurements were available (with some station-to-station variability) for the year 2008-2009 and the GUAN measurements were mostly from 2009. The locations of the stations are shown in Fig. 2. 

It is difficult to extract precise Qd values from ambient air sampling data. Plots of Equation (11) are constructed by measuring Kp on days when temperatures vary (Bidleman et al., 1986 Foreman and Bidleman, 1990 Gustafson and Dickhut, 1997 Pankow, 1991 Yamasaki et al., 1982). Unfortunately, these experimental Kp estimates also reflect the day-to-day variations in relative humidity and aerosol properties. As a result, confidence intervals around Qd are typically large (Bidleman et al., 1986 Pankow, 1991). Moreover, differences in the rates at which gases equilibrate with particles on hot and cold days (Kamens... 

As in the stratosphere, in situ ion composition measurements should offer an enormous potential for neutral trace gas detection. Likely candidates for PACIMS trace gas detection are the reactant trace gases discussed above. Diagnostic applications for probing aerosol properties also seem promising. Since tropospheric cluster ions are relatively large, they should resemble aerosol solution droplets. 

The first stage of the consideration of the effect of aerosol on climate is the modeling of aerosol properties. The models (based on statistically reliable field-measurements data) are to parameterize such characteristics as complex refractive index of particles m = n — ki), their shape and size distribution, vertical profile of aerosol concentrations, as well as variability of these parameters in time and due to humidity. 

In the sections that follow, mathematical methods for characterizing aerosol size and chemical properties are discussed. These are primarily of a definitional nature and are needed to provide a common basis for discussing the broad range of aerosol properties and behavior. However, aerosol characterization does not provide, directly, information on the mechanisms of aerosol formation, or temporal and spatial changes in the aerosol—that is, aerosol transport processes and aerosol tlynatnics. These and related topics are covered in later chapters. Advances in aerosol instrumentation have made it possible to measure many of the most important parameters necessary to characterize aerosols (Chapter 6). However, much rejnains to be done in developing aerosol instrumentation for research as well as industrial and atmospheric applications. 

The mass eoncemralion is the most commonly measured aerosol property ... 

Aerosol measurement instruments can be conveniently classified according to the type and quantity of information they provide about aerosol properties. The physical principles on which the instniments are based are of secondary importance in this classification scheme, and indeed the instruments can be considered black boxes. This approach makes it possible... 

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