Source apportionment of atmospheric trace gases and particulate matter: comparison of log-ratio and traditional approaches

In this paper we compare multivariate methods using both traditional approaches, which ignore issues of closure and provide relatively simple methods to deal with censored or missing data, and log-ratio methods to determine the sources of trace constituents in the atmosphere. The data set examined was collected from April to July 2008 at a sampling site near Woods Hole, Massachusetts, along the northeastern United States Atlantic coastline. The data set consists of trace gas mixing ratios (O3, SO2, NOx, elemental mercury [Hgo], and reactive gaseous mercury [RGM]), and concentrations of trace elements in fine (<2.5 μm) particulate matter (Al, As, Ba, Ca, Cd, Ce, Co, Cs, Fe, Ga, Hg, K, La, Mg, Mn, Na, P, Pb, Rb, Sb, Sr, Th, Ti, V, Y, and Zn) with varying percentages of censored values for each species. The data were separated into two subcompositions: s1, which is comprised by RGM and particulate Hg (HgP), which are both highly censored; and s2 which includes all of the trace elements associated with particulate matter except Hg, and the trace gases O3, SO2, NOx, and Hgo. Principal factor analysis (PFA) was successful in determining the primary sources for constituents in s2 using both traditional and log-ratio approaches. Using the traditional approach, regression between factor scores and RGM and particulate Hg concentrations suggested that none of the sources identified during PFA led to positive contributions of either reactive mercury compound. This finding is counter to most conventional thinking and is likely specious, resulting from removal of censored data (up to >80% of the entire dataset) during the analysis. Log-ratio approaches to find relationships between constituents comprising s2 with RGM and HgP (i.e., s1) focused on log-ratio correlation and regression analyses of alr-transformed data, using Al as the divisor. Regression models accounted for large fractions of the variance in concentrations of the two reactive mercury species and generally agreed with conceptualizations about the formation and behavior of these species. An analysis of independence between the subcompositions demonstrated that the behavior of the two constituents comprising s1 (i.e., RGM and HgP) is dependent on changes in s2. Our findings suggest that although problems related to closure are largely unknown or ignored in the atmospheric sciences, much insight can be gleaned from the application of log-ratio methods to atmospheric chemistry data

Mercury Contamination of Aquatic Ecosystems

This United States Geological Survey (USGS) factsheet contains information about US mercury contamination. Issues discussed include how mercury becomes a toxicological problem through bioaccumulation, human effects of mercury toxicity, and levels of atmospheric mercury. Mercury levels in fish are examined to determine how mercury gets into the environment and into the food chain. Educational levels: General public

Mercury distribution and mobility at the abandoned Puhipuhi mercury mine, Northland, New Zealand

The United Nations 2013 Minamata Convention advocates for updated environmental assessments of potential point-source sites of mercury contamination, including historic closed or abandoned mines. The Puhipuhi mercury mine (Northland), a historic and abandoned mine site, is located near one of the headwaters of the Wairoa River. In this study, total mercury levels in soils and sediments (37.8–1748 µg g−1), total and methylated mercury in waters (69.6–240 ng L−1 and 0.637–1.95 ng L−1, respectively), and elemental mercury in air (0.06–0.5 ng m−3) were measured to assess the probability and form of mercury release from the site to the surrounding natural environment. Results showed that mercury concentrations at the site are elevated compared to regional backgrounds and further work is necessary to determine how mercury may be transported from the site

A hypolimnetic mass balance of mercury from a dimictic lake: Results from the METAALICUS project

Our ability to determine the fate and transport of newly deposited mercury, from that of historically deposited mercury, was recently demonstrated by the Mercury Experiment To Assess Atmospheric Loading In Canada and the United States (METAALICUS). The METAALICUS project is a whole-watershed amendment study where different stable isotopes of mercury were applied to three watershed compartments totaling ~53 Hectares: the upland, the wetland, and the surface of a dimictic lake in northwesten Ontario, Canada. Each compartment received approximately 5 times the annual background atmospheric deposition for the region. In the lake, the spike was divided into 9 bi-week injections administered over several hours through the wash of a trolling motor while circling the lake. The spike was added at dusk to limit photo reduction and evasion of elemental mercury. Results from two years of data show that new mercury is extremely particle reactive. Implications for the availability of newly deposited mercury for methylation, and a well-constrained mass balance of the hypolimnetic mercury cycle, will be presented

Seasonality and the isotope hydrology of Lochnagar, a Scottish mountain lake : implications for palaeoclimate reasearch

The relationship between isotope ratios in precipitation and lake waters was monitored by bi-weekly measurements taken over a five and a half year period between May 2000 and September 2005 (a period of 1964 days) at Lochnagar, a remote mountain lake in eastern Scotland. Short-term changes in the oxygen isotope composition of lake water (18OL) at Lochnagar follow a seasonal pattern similar to isotopes in local precipitation (18OP), however changes in catchment residence time, snow accumulation, lake ice cover and lake stratification modify the temporal structure of 18OL over the seasonal cycle. Of particular importance is precipitation amount, which controls catchment and lake residence times, and determines the degree of phase lag and amplitude change between 18OL and 18OP. A simple mass balance model replicates these effects and demonstrates that the degree of phase lag and amplitude reduction is predictable given known input/volume ratio. The implications of these observations for the use of 18O records in palaeoclimatology are important, since it is rare that authigenic and biogenic minerals or organic compounds (from which 18O and/or 2H can be measured) are produced in a lake evenly throughout the year

The role of terrestrial vegetation in atmospheric Hg deposition: Pools and fluxes of spike and ambient Hg from the METAALICUS experiment

As part of the Mercury Experiment to Assess Atmospheric Loading in Canada and the U.S. (METAALICUS), different stable Hg(II) isotope spikes were applied to the upland and wetland areas of a boreal catchment between 2001 and 2006 to examine retention of newly deposited Hg(II). In the present study, a Geographical Information Systems (GIS)-based approach was used to quantify canopy and ground vegetation pools of experimentally applied upland and wetland spike Hg within the METAALICUS watershed over the terrestrial loading phase of the experiment. A chemical kinetic model was also used to describe the changes in spike Hg concentrations of canopy and ground vegetation over time. An examination of the fate of spike Hg initially present on canopy vegetation using a mass balance approach indicated that the largest percentage flux from the canopy over one year post-spray was emission to the atmosphere (upland: 45%; wetland: 71%), followed by litterfall (upland: 14%; wetland: 10%) and throughfall fluxes (upland: 12%; wetland: 9%) and longer term retention of spike in the forest canopy (11% for both upland and wetland). Average half-lives (t 1/2) of spike on deciduous (110 30days) and coniferous (180 40days) canopy and ground vegetation (890 620days) indicated that retention of new atmospheric Hg(II