Search for: All records

Atmospheric Hg^IIconcentrations at a given site are linearly related to the amount of Hg^IIlost from the atmosphere during precipitation. The slope from DCS measurement data (a) could be used to correct the older data which were biased low (b). 

Accurate measurement of atmospheric reactive mercury (RM) presents analytical challenges due to its reactivity and ultra-trace concentrations. In the last decade, use of the University of Nevada, Reno – Reactive Mercury Active System (RMAS) for RM measurements has increased since it has been shown to be more accurate than the industry standard, the Tekran 2537/1130/1135 system. However, RMAS measurements also have limitations, including long time resolution and sampling biases associated with membranes used for RM sampling. We therefore investigated the use of higher sampling flow rates to reduce sampling time and tested alternative membrane materials using both ambient air sampling and controlled laboratory experiments with a gaseous oxidized mercury (GOM) calibrator. Results indicated that increasing the RMAS sampling flow had a negative impact on determined RM concentrations. RM concentrations at 2 L min−1 were 10% and 30–50% lower than at 1 L min−1 in spring/summer and winter, respectively. However, the chemical composition of RM captured on membranes was not impacted by the increased flow rate. Membranes currently used in the RMAS performed better than numerous alternatives with similar composition, retaining Hg more efficiently. Both ambient air sampling and laboratory experiments revealed that membranes designed to retain only particulate-bound mercury (PBM) also retained significant amounts of GOM. PBM membranes based on borosilicate glass designs retained more than 70% of GOM. 

Abstract. Methodologies for identifying atmospheric oxidized mercury (HgII) compounds, including particulate-bound HgII (HgII(p)) and gaseous oxidized mercury (HgII(g)), by mass spectrometry are currently under development. This method requires preconcentration of HgII for analysis due to high instrument detection limits relative to ambient HgII concentrations. The objective of this work was to identify and test materials for quantitative capture of HgII from the gas phase and to suggest potential surfaces onto which HgII can be collected, thermally desorbed, and characterized using mass spectrometry methods. From the literature, several compounds were identified as potential sorbent materials and tested in the laboratory for uptake of gaseous elemental mercury (Hg0) and HgII(g) (permeated from a HgBr2 salt source). Chitosan, α-Al2O3, and γ-Al2O3 demonstrated HgII(g) capture in ambient air laboratory tests, without sorbing Hg0 under the same conditions. When compared to cation exchange membranes (CEMs), chitosan captured a comparable quantity of HgII(g), while ≤90 % of loaded HgII(g) was recovered from α-Al2O3 and γ-Al2O3. When deployed in the field, the capture efficiency of chitosan decreased compared to CEMs, indicating that environmental conditions impacted the sorption efficiency of this material. The poor recovery of HgII from the tested materials compared to CEMs in the field indicates that further identification and exploration of alternative sorbent materials are required to advance atmospheric mercury chemistry analysis by mass spectrometry methods. 

There is much uncertainty regarding the sources of reactive mercury (RM) compounds and atmospheric chemistry driving their formation. This work focused on assessing the chemistry and potential sources of reactive mercury measured in Reno, Nevada, United States, using 1 year of data collected using Reactive Mercury Active System. In addition, ancillary meteorology and criteria air pollutant data, Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) analyses, and a generalized linear model were applied to better understand reactive mercury observations. During the year of sampling, a fire event impacted the sampling site, and gaseous elemental Hg and particulate-bound mercury concentrations increased, as did Hg^II-S compounds. Data collected on a peak above Reno showed that reactive mercury concentrations were higher at higher elevation, and compounds found in Reno were the same as those measured on the peak. HYSPLIT results demonstrated RM compounds were generated inside and outside of the basin housing Reno. Compounds were sourced from San Francisco, Sacramento, and Reno in the fall and winter, and from long-range transport and the marine boundary layer during the spring and summer. The generalized linear model produced correlations that could be explained; however, when applying the model to similar data collected at two other locations, the Reno model did not predict the observations, suggesting that sampling location chemistry and concentration cannot be generalized.