Source apportionment of atmospheric trace gases and particulate matter: Comparison of log-ratio and traditional approaches
Year: 2011
Type: book-chapter
Abstract: In this paper we compare multivariate methods using both traditional approaches, which\nignore issues of closure and provide relatively simple methods to deal with censored or\nmissing data, and log-ratio methods to determine the sources of trace constituents in the\natmosphere. The data set examined was collected from April to July 2008 at a sampling site\nnear Woods Hole, Massachusetts, along the northeastern United States Atlantic coastline.\nThe data set consists of trace gas mixing ratios (O3, SO2, NOx, elemental mercury [Hgo\n], and\nreactive gaseous mercury [RGM]), and concentrations of trace elements in fine (<2.5 µm)\nparticulate matter (Al, As, Ba, Ca, Cd, Ce, Co, Cs, Fe, Ga, Hg, K, La, Mg, Mn, Na, P, Pb,\nRb, Sb, Sr, Th, Ti, V, Y, and Zn) with varying percentages of censored values for each\nspecies.\n The data were separated into two subcompositions: s1, which is comprised by RGM and\nparticulate Hg (HgP), which are both highly censored; and s2 which includes all of the trace\nelements associated with particulate matter except Hg, and the trace gases O3, SO2, NOx, and\nHgo\n. Principal factor analysis (PFA) was successful in determining the primary sources for\nconstituents in s2 using both traditional and log-ratio approaches. Using the traditional\napproach, regression between factor scores and RGM and particulate Hg concentrations\nsuggested that none of the sources identified during PFA led to positive contributions of\neither reactive mercury compound. This finding is counter to most conventional thinking and\nis likely specious, resulting from removal of censored data (up to >80% of the entire dataset)\nduring the analysis.\n Log-ratio approaches to find relationships between constituents comprising s2 with RGM\nand HgP (i.e., s1) focused on log-ratio correlation and regression analyses of alr-transformed\ndata, using Al as the divisor. Regression models accounted for large fractions of the variance\nin concentrations of the two reactive mercury species and generally agreed with\nconceptualizations about the formation and behavior of these species. An analysis of\nindependence between the subcompositions demonstrated that the behavior of the two\nconstituents comprising s1 (i.e., RGM and HgP) is dependent on changes in s2. Our findings\nsuggest that although problems related to closure are largely unknown or ignored in the\natmospheric sciences, much insight can be gleaned from the application of log-ratio methods\nto atmospheric chemistry data
Institution: United States Geological Survey
Language: English
Subfield: Atmospheric Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2181479849