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Horowitz, Hannah

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Horowitz

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Hannah

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Horowitz, Hannah

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2014 - 20163

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Author's Publications: search.filters.isAuthorOfPublication.fd8a1dba-60ee-4362-a6ad-471d138db435

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    Global Biogeochemical Implications of Mercury Discharges from Rivers and Sediment Burial
    (American Chemical Society (ACS), 2014) Amos, Helen; Jacob, Daniel; Kocman, David; Horowitz, Hannah; Zhang, Yanxu; Dutkiewicz, Stephanie; Horvat, Milena; Corbitt, Elizabeth Sturges; Krabbenhoft, David P.; Sunderland, Elynor
    Rivers are an important source of mercury (Hg) to marine ecosystems. Based on an analysis of compiled observations, we estimate global present-day Hg discharges from rivers to ocean margins are 27 plus or minus 13 Mmol a super(-1) (5500 plus or minus 2700 Mg a super(-1)), of which 28% reaches the open ocean and the rest is deposited to ocean margin sediments. Globally, the source of Hg to the open ocean from rivers amounts to 30% of atmospheric inputs. This is larger than previously estimated due to accounting for elevated concentrations in Asian rivers and variability in offshore transport across different types of estuaries. Riverine inputs of Hg to the North Atlantic have decreased several-fold since the 1970s while inputs to the North Pacific have increased. These trends have large effects on Hg concentrations at ocean margins but are too small in the open ocean to explain observed declines of seawater concentrations in the North Atlantic or increases in the North Pacific. Burial of Hg in ocean margin sediments represents a major sink in the global Hg biogeochemical cycle that has not been previously considered. We find that including this sink in a fully coupled global biogeochemical box model helps to balance the large anthropogenic release of Hg from commercial products recently added to global inventories. It also implies that legacy anthropogenic Hg can be removed from active environmental cycling on a faster time scale (centuries instead of millennia). Natural environmental Hg levels are lower than previously estimated, implying a relatively larger impact from human activity.
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    Historical Mercury Releases from Commercial Products: Global Environmental Implications
    (American Chemical Society (ACS), 2014) Horowitz, Hannah; Jacob, Daniel; Amos, Helen; Streets, David G.; Sunderland, Elynor
    The intentional use of mercury (Hg) in products and processes (“commercial Hg”) has contributed a large and previously unquantified anthropogenic source of Hg to the global environment over the industrial era, with major implications for Hg accumulation in environmental reservoirs. We present a global inventory of commercial Hg uses and releases to the atmosphere, water, soil, and landfills from 1850 to 2010. Previous inventories of anthropogenic Hg releases have focused almost exclusively on atmospheric emissions from “byproduct” sectors (e.g., fossil fuel combustion). Cumulative anthropogenic atmospheric Hg emissions since 1850 have recently been estimated at 215 Gg (only including commercial Hg releases from chlor-alkali production, waste incineration, and mining). We find that other commercial Hg uses and nonatmospheric releases from chlor-alkali and mining result in an additional 540 Gg of Hg released to the global environment since 1850 (air: 20%; water: 30%; soil: 30%; landfills: 20%). Some of this release has been sequestered in landfills and benthic sediments, but 310 Gg actively cycles among geochemical reservoirs and contributes to elevated present-day environmental Hg concentrations. Commercial Hg use peaked in 1970 and has declined sharply since. We use our inventory of historical environmental releases to force a global biogeochemical model that includes new estimates of the global burial in ocean margin sediments. Accounting for commercial Hg releases improves model consistency with observed atmospheric concentrations and associated historical trends.
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    Observed decrease in atmospheric mercury explained by global decline in anthropogenic emissions
    (Proceedings of the National Academy of Sciences, 2016) Zhang, Yanxu; Jacob, Daniel; Horowitz, Hannah; Chen, Long; Amos, Helen; Krabbenhoft, David P.; Slemr, Franz; St. Louis, Vincent L.; Sunderland, Elynor
    Anthropogenic mercury poses risks to humans and ecosystems when converted to methylmercury. A longstanding conundrum has been the apparent disconnect between increasing global emissions trends and measured declines in atmospheric mercury in North America and Europe. This work shows that locally deposited mercury close to coal-fired utilities has declined more rapidly than previously anticipated because of shifts in speciation from air pollution control technology targeted at SO2 and NOx. Reduced emissions from utilities over the past two decades and the phase-out of mercury in many commercial products has led to lower global anthropogenic emissions and associated deposition to ecosystems. This implies that prior policy assessments underestimated the regional benefits of declines in mercury emissions from coal-fired utilities.