Temporally delineated sources of major chemical species in high Arctic snow

Katrina M Macdonald,Nathan Chellman,Daniel Kunkel,Richard Leaitch,Desiree Toom,Ying Duan Lei,Mike Elsasser,Alina Chivulescu,Lin Huang,Greg J Evans,Sangeeta Sharma,Cheol-Heon Jeong,Heiko Bozem,Andrew Platt,Jonathan P D Abbatt,Joseph R Mcconnell

doi:10.5194/acp-18-3485-2018

Abstract

Abstract. Long-range transport of aerosol from lower latitudes to the high Arctic may be a significant contributor to climate forcing in the Arctic. To identify the sources of key contaminants entering the Canadian High Arctic an intensive campaign of snow sampling was completed at Alert, Nunavut, from September 2014 to June 2015. Fresh snow samples collected every few days were analyzed for black carbon, major ions, and metals, and this rich data set provided an opportunity for a temporally refined source apportionment of snow composition via positive matrix factorization (PMF) in conjunction with FLEXPART (FLEXible PARTicle dispersion model) potential emission sensitivity analysis. Seven source factors were identified: sea salt, crustal metals, black carbon, carboxylic acids, nitrate, non-crustal metals, and sulfate. The sea salt and crustal factors showed good agreement with expected composition and primarily northern sources. High loadings of V and Se onto Factor 2, crustal metals, was consistent with expected elemental ratios, implying these metals were not primarily anthropogenic in origin. Factor 3, black carbon, was an acidic factor dominated by black carbon but with some sulfate contribution over the winter-haze season. The lack of K+ associated with this factor, a Eurasian source, and limited known forest fire events coincident with this factor's peak suggested a predominantly anthropogenic combustion source. Factor 4, carboxylic acids, was dominated by formate and acetate with a moderate correlation to available sunlight and an oceanic and North American source. A robust identification of this factor was not possible; however, atmospheric photochemical reactions, ocean microlayer reaction, and biomass burning were explored as potential contributors. Factor 5, nitrate, was an acidic factor dominated by NO3−, with a likely Eurasian source and mid-winter peak. The isolation of NO3− on a separate factor may reflect its complex atmospheric processing, though the associated source region suggests possibly anthropogenic precursors. Factor 6, non-crustal metals, showed heightened loadings of Sb, Pb, and As, and correlation with other metals traditionally associated with industrial activities. Similar to Factor 3 and 5, this factor appeared to be largely Eurasian in origin. Factor 7, sulfate, was dominated by SO42− and MS with a fall peak and high acidity. Coincident volcanic activity and northern source regions may suggest a processed SO2 source of this factor.

Highlights

Introduction and backgroundObservations of Arctic climate have shown pronounced changes over recent years, including a rapid rise in surface temperature and the loss of sea ice and snow cover, with adverse local and global consequences (AMAP, 2017; Hartmann et al, 2013)
A recent study by Xu et al (2017) analyzing airborne measurement from a similar time period as this study found about 90 % of BC to likely be anthropogenic in source, primarily from Eurasia, supporting the assessment above
Positive matrix factorization of the snow measurements was found to resolve seven factors with good solution diagnostics, interpretability, and agreement with measured values. These factors were identified based on composition, seasonal contribution, and FLEXPART-predicted major source regions: sea salt, crustal metals, black carbon, carboxylic acids, nitrate, non-crustal metals, and sulfate

Summary

Introduction

Observations of Arctic climate have shown pronounced changes over recent years, including a rapid rise in surface temperature and the loss of sea ice and snow cover, with adverse local and global consequences (AMAP, 2017; Hartmann et al, 2013). Such changes in Arctic climate have been tied to contaminants within the Arctic atmosphere and snow, especially light-absorbing compounds such as black carbon. Macdonald et al.: Temporally delineated sources of major chemical species in high Arctic snow (BC) which can warm the surface and atmosphere (Clarke and Noone, 1985; Hansen and Nazarenko, 2004; Bond et al, 2013; Jiao et al, 2014). Understanding the sources of these pollutants is a critical step in the development of control and mitigation strategies to protect the vulnerable Arctic environment

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Conclusion