Impact of Measurement Uncertainties on Receptor Modeling of Speciated Atmospheric Mercury.

I Cheng,L Zhang,X Xu

doi:10.1038/srep20676

Abstract

Gaseous oxidized mercury (GOM) and particle-bound mercury (PBM) measurement uncertainties could potentially affect the analysis and modeling of atmospheric mercury. This study investigated the impact of GOM measurement uncertainties on Principal Components Analysis (PCA), Absolute Principal Component Scores (APCS), and Concentration-Weighted Trajectory (CWT) receptor modeling results. The atmospheric mercury data input into these receptor models were modified by combining GOM and PBM into a single reactive mercury (RM) parameter and excluding low GOM measurements to improve the data quality. PCA and APCS results derived from RM or excluding low GOM measurements were similar to those in previous studies, except for a non-unique component and an additional component extracted from the RM dataset. The percent variance explained by the major components from a previous study differed slightly compared to RM and excluding low GOM measurements. CWT results were more sensitive to the input of RM than GOM excluding low measurements. Larger discrepancies were found between RM and GOM source regions than those between RM and PBM. Depending on the season, CWT source regions of RM differed by 40–61% compared to GOM from a previous study. No improvement in correlations between CWT results and anthropogenic mercury emissions were found.

Highlights

Gaseous oxidized mercury (GOM) and particle-bound mercury (PBM) are operationally-defined Hg(II) compounds, such as mercuric halides, mercuric sulfate, mercuric nitrite, and mercuric hydroxide[2]
Four components were extracted from Principal Components Analysis (PCA) of the reactive mercury (RM) dataset, which is consistent with the number of components from PCA of the SpecHg in a previous study[12]
The percent variance of the RM data explained by the components differed from SpecHg by 3–4%, which suggests the use of RM changes the percent variance explained by each component slightly

Summary

Introduction

GOM and PBM are operationally-defined Hg(II) compounds, such as mercuric halides, mercuric sulfate, mercuric nitrite, and mercuric hydroxide[2]. Other sources of measurement uncertainties during sampling include ozone and water vapor interferences[4,5,6], chemical reactions[2,7,8], and variable collection efficiencies depending on the form of GOM9,10. These uncertainties are believed to be contributing to the underestimation of GOM. The first approach combines GOM and PBM into a single reactive Hg compound, instead of separating GOM and PBM as in previous studies. Results from this study can provide an uncertainty assessment of the previously-obtained atmospheric Hg receptor modeling results

Methods

Results

Discussion

Conclusion