Atmospheric mercury speciation and mercury in snow over time at Alert, Canada

A. Steffen,G. Lawson,W. R. Leaitch,J. Bottenheim,A. Cole,R. Ebinghaus

doi:10.5194/acp-14-2219-2014

Abstract

Abstract. Ten years of atmospheric mercury speciation data and 14 years of mercury in snow data from Alert, Nunavut, Canada, are examined. The speciation data, collected from 2002 to 2011, includes gaseous elemental mercury (GEM), particulate mercury (PHg) and reactive gaseous mercury (RGM). During the winter-spring period of atmospheric mercury depletion events (AMDEs), when GEM is close to being completely depleted from the air, the concentration of both PHg and RGM rise significantly. During this period, the median concentrations for PHg is 28.2 pgm−3 and RGM is 23.9 pgm−3, from March to June, in comparison to the annual median concentrations of 11.3 and 3.2 pgm−3 for PHg and RGM, respectively. In each of the ten years of sampling, the concentration of PHg increases steadily from January through March and is higher than the concentration of RGM. This pattern begins to change in April when the levels of PHg peak and RGM begin to increase. In May, the high PHg and low RGM concentration regime observed in the early spring undergoes a transition to a regime with higher RGM and much lower PHg concentrations. The higher RGM concentration continues into June. The transition is driven by the atmospheric conditions of air temperature and particle availability. Firstly, a high ratio of the concentrations of PHg to RGM is reported at low temperatures which suggests that oxidized gaseous mercury partitions to available particles to form PHg. Prior to the transition, the median air temperature is −24.8 °C and after the transition the median air temperature is −5.8 °C. Secondly, the high PHg concentrations occur in the spring when high particle concentrations are present. The high particle concentrations are principally due to Arctic haze and sea salts. In the snow, the concentrations of mercury peak in May for all years. Springtime deposition of total mercury to the snow at Alert peaks in May when atmospheric conditions favour higher levels of RGM. Therefore, the conditions in the atmosphere directly impact when the highest amount of mercury will be deposited to the snow during the Arctic spring.

Highlights

Attention to mercury has increased in the scientific community over the past two decades because of the interesting springtime atmospheric chemistry in the high Arctic and its potential impact on the environment
During the winter-spring period of atmospheric mercury depletion events (AMDEs), when gaseous elemental mercury (GEM) is close to being completely depleted from the air, the concentration of both PHg and reactive gaseous mercury (RGM) rise significantly
A high ratio of the concentrations of PHg to RGM is reported at low temperatures which suggests that oxidized gaseous mercury partitions to available particles to form PHg

Summary

Introduction

Attention to mercury has increased in the scientific community over the past two decades because of the interesting springtime atmospheric chemistry in the high Arctic and its potential impact on the environment. The atmospheric processes that dominate the springtime oxidation and deposition of mercury may lead to the deposition of some of this long range transported mercury onto the Arctic surface. Many studies have reported the decrease in GEM and a concurrent increase in oxidized mercury (PHg and RGM) and the connection of this chemistry to spring time ozone and halogen chemistry (Lindberg et al, 2001; Lindberg et al, 2002; Aspmo et al, 2005; Kirk et al, 2006; Cobbett et al, 2007; Simpson et al, 2007; Dastoor et al, 2008; Steffen et al, 2008; Steen et al, 2011). While atmospheric mercury speciation data in the Arctic air have been collected at several sites (Aspmo et al, 2005; Sprovieri et al, 2005; Kirk et al, 2006; Skov et al, 2006; Cobbett et al, 2007; Steen et al, 2011; Moore et al, 2012; Cole et al, 2013; Steffen et al, 2013; Brooks et al, 2006), few longterm (more than 5 years) mercury speciation measurements at temperate regions have been published and the Alert data set is the only such Arctic data set (Cole et al, 2013)

Methods

Results

Conclusion