Cluster analysis of atmospheric

Cluster Analysis of Chemical Compositions of Individual Atmospheric Particles Data... 

Beddows DCS, Dall osto M, Harrison RM (2009) Cluster analysis of rural, urban, and curbside atmospheric particle size data. Environ Sci Technol 43 4694-4700... 

In our laboratory, we have applied some of the methods and experimental technologies of cluster science to the analysis of atmospheric processes and this article will summarize our findings. 

T. W. Shatruck, M. S. Getmani, and P. R. Buscek, in Environmental Applications of Che-mometrics. J. J. Breen, Ed., American Chemical Socie, Washington, DC, 1985. Cluster Analysis of Chemical Compositions of Individual Atmospheric Particles Data. 

The multivariate techniques which reveal underlying factors such as principal component factor analysis (PCA), soft Independent modeling of class analogy (SIMCA), partial least squares (PLS), and cluster analysis work optimally If each measurement or parameter Is normally distributed In the measurement space. Frequency histograms should be calculated to check the normality of the data to be analyzed. Skewed distributions are often observed In atmospheric studies due to the process of mixing of plumes with ambient air. 

K-means cluster analysis is an excellent method for the reduction of individual-partide datai if extra clusters are used to allow for the non-spherical shape and natural variability of atmospheric particles. The "merge" method for choosing seedpoints is useful for detecting the types of lew abundance particles that are interesting for urban atmospheric studies. Application to the Phoenix aerosol suggests that the ability to discriminate between various types of crustal particles may yield valuable information in addition to that derived from particle types more commonly associated with anthropogenic activity. 

Contrary to the case of anionic reactions, the formation of a strong proton-bound dimer for alcohols suggests that nucleophilic displacement may actually involve a frontside attack. Recent experiments carried out at atmospheric pressure by Speranza and Angelini (1980) using radiolytic techniques with isolation and glc analysis of neutral products reveal some interesting stereochemistry. For example, the reaction of protonated epoxy-rra/is-but-2-ene with H20 results in 98% inversion of configuration, while a similar reaction with cis-1 -chloro-4-methylcyclohexane results in approximately 80% of tro/is-4-methylcyclohexanol. With the high pressures utilized and with the possible participation of cluster ions a likelihood in this case, the data are consistent with a Walden inversion for these cases. 

Size-dependent structure and properties of Earth materials impact the geological processes they participate in. This topic has not been fully explored to date. Chapters in this volume contain descriptions of the inorganic and biological processes by which nanoparticles form, information about the distribution of nanoparticles in the atmosphere, aqueous environments, and soils, discussion of the impact of size on nanoparticle structure, thermodynamics, and reaction kinetics, consideration of the nature of the smallest nanoparticles and molecular clusters, pathways for crystal growth and colloid formation, analysis of the size-dependence of phase stability and magnetic properties, and descriptions of methods for the study of nanoparticles. These questions are explored through both theoretical and experimental approaches. 

Secondary ion mass spectrometry (SIMS) has also found application in the analysis of organic compounds not prone to thermal evaporation. By this technique sulfanilic acid gave fair abundancies of [M —H] ions15, when bombarded with low primary-ion current densities on a silver target. Sulfonic acids were successfully tested by atmospheric-pressure ion evaporation mass spectrometry and found to produce characteristic negative cluster ions16. 

FIGURE 11.3 An example of the formation of adducts in drift tubes can be seen in mobility spectra from ESI-IM-MS analysis of a solution of a pharmaceutical, lamivudine miz 230), of PEG (mIz 635, n = 14), and for a lamivudine/PEG complex (mIz 864, n = 14) overlaid with normalized intensities. This example occurred with special efforts to modify the supporting atmosphere of an IMS drift tube and was attributed to clusters formed in the ESI spray. In this instance, the ion clnsters were strongly held and had lifetimes enough to pass through the IMS drift region. 

MALDI is the dominant ionization source choice for MSI however, it is not without drawbacks. The application of MALDI matrix on top of the tissue surface complicates the analysis by adding potentially isobaric matrix cluster ions that may obscure the drug compound. Careful selection of MALDI matrix can reduce the matrix effect. An alternative would be to either use the water native to the tissue as a matrix such as with IR-MALDI or altogether eliminate the need for matrix. DESI is an atmospheric pressure technique that permits the direct analysis of surface samples, including tissue sections, with minimal sample preparation (Takats et al., 2004 Cooks et al., 2006). In contrast to MALDI—MSI, no matrix is required however, the spatial resolution for DESI—MSI is worse when compared to MALDI or SIMS imaging experiments. 

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