Ground-level Particulate Sulphate and Gaseous Sulphur Dioxide Downwind of an Aluminium Smelter

Dane Blanchard,Julian Aherne

doi:10.4209/aaqr.200528

Abstract

ABSTRACT Particulate sulphate (pSO42–) is an atmospheric pollutant known to affect human/environmental health and global radiative-forcing. The Rio Tinto (RT) aluminium smelting facility in Kitimat, British Columbia, is the primary source of sulphur dioxide (SO2) emissions to the surrounding Kitimat Valley, a relatively isolated and unpolluted region. A network of active two-stage filter-packs and passive-diffusive samplers was established between June 2017 to October 2018 with the objective to evaluate the spatiotemporal variation and relative contribution of pSO42– to total anthropogenic atmospheric oxidized sulphur (SOx = SO2 + pSO42–). Average pSO42– across all sites (n = 9) was 0.41 µg m–3 (24–48 hour exposures) and ranged from 0.03 to 2.03 µg m–3. In contrast, average filter-pack SO2 ranged from 0.11 to 8.9 µg m–3 (during the same exposure periods). The filter-pack pSO42–/SOx concentration ratio (Fs) increased downwind of the smelter, indicating that the relative concentration of pSO42– increased with distance from the smelter. Furthermore, the increasing pSO42–/vanadium (V) ratio (used as a tracer of smelter emissions) relative to distance confirmed particulate formation was occurring within the emission plume during the sampling period. Irrespective of in-plume aerosol formation, pSO42– contributed a relatively minor fraction of total atmospheric SOx within the emission plume (field campaign averages Fs 1.0 µg S m–3).

Highlights

Anthropogenic emissions of gaseous sulphur dioxide (SO2) can negatively impact the environment through the deposition of acidic sulphur (S) species, such as sulphuric acid (H2SO4) (Parungo et al, 1987)
Air currents originating from inland BC or the Pacific are forced by the prominent topography of the surrounding region, steering predominant winds north or south along the Kitimat Valley
The highest average temperature during the study was recorded in July of 2018 (20.3°C), while the lowest occurred in February 2018 (–2.7°C)

Summary

Introduction

Anthropogenic emissions of gaseous sulphur dioxide (SO2) can negatively impact the environment through the deposition of acidic sulphur (S) species, such as sulphuric acid (H2SO4) (Parungo et al, 1987). Following release to the atmosphere, SO2 can undergo several oxidation reactions to form H2SO4, which can further condense to become particulate sulphate (pSO42–) (Friedlander, 1978; Huntzicker et al, 1984). These particulates ( referred to as aerosol sulphate) are of unique concern owing to their longevity in the atmosphere and potential impact to environmental and human health (Davidson et al, 2005; Hains et al, 2008; Lee et al, 2011). PSO42– can contribute to acidic deposition via processes of wet and dry removal (Nicholson and Davies, 1987)

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Conclusion