. 2016 Jan 4;113(3):526–531. doi: 10.1073/pnas.1516312113

Table 1.

Observed 1990 to present trends in atmospheric Hg⁰ concentrations and Hg^II wet deposition fluxes since the 1990s

Period	Location (network)	Trend, % y⁻¹^a	Source
Atmospheric Hg⁰ concentrations
1995 to 2010	Canada (CAMNet)	−1.6 ± 0.8^b^,^c	Ref. 7
1996 to 2004	Cape Point, South Africa	−1.3 ± 0.3^c^,^d	Ref. 11
1990 to 1996	Wank, Germany	−6.1 ± 1.1^c^,^d	Ref. 12
1996 to 2013	Mace Head, Ireland	−1.3 ± 0.2^c^,^e	Ref. 13
1990 to 2009	North Atlantic, cruises	−2.5 ± 0.5^c^,^d	Ref. 6
1990 to 2009	South Atlantic	Not significant	Ref. 6
2000 to 2009	Alert, Canada	−0.9 ± 0.5^f^,^g	Ref. 28
2000 to 2009	Zeppelin, Norway	Not significant	Ref. 28
2008 to 2013	United States (AMNet)	Not significant^c^,^e	This study
2005 to 2013	Experimental Lakes Area, Canada	−2.2 ± 0.6^c^,^e	This study
1990 to 2011	Western Europe (EMEP)	−2.1 ± 0.5^c^,^e	This study
1994 to 2012	North of 60° N	Not significant^c^,^e	This study
2005 to 2014	Free troposphere (CARIBIC)	Not significant^c^,^e^,^h	This study
2002 to 2013	Mauna Loa Observatory, Hawaii	Not significant^c^,^d	Ref. 14
Hg^II wet deposition
1996 to 2008	North America (MDN)	Not significant^c^,ⁱ	Ref. 9
1996 to 2008	Western Europe (EMEP)	−1.5 ± 0.5	Ref. 9
1998 to 2005	Northeast United States (MDN)	−1.7 ± 0.5^c^,^j	Ref. 15
	Midwest United States	−3.5 ± 0.7
	Southeast United States	Not significant
1996 to 2005	Northeast United States (MDN)	−2.1 ± 0.9^g^,^k^,^l	Ref. 8
	Midwest United States	−1.8 ± 0.3
	Southeast United States	−1.3 ± 0.3
	West United States	−1.4 ± 0.4
2002 to 2008	Northeast United States (MDN)	Not significant^g^,^l	Ref. 16
2002 to 2008	Midwest United States	Not significant	Ref. 16
2004 to 2010	Northeast United States (MDN)	−4.1 ± 0.5^c^,^m	Ref. 26
	Midwest United States	−2.7 ± 0.7
	Southeast United States	Not significant
	Western United States	Not significant
1996 to 2013	North America, MDN	−1.6 ± 0.3^c^,^j^,ⁿ	This study
1990 to 2012	Western Europe, EMEP	−2.2 ± 0.6	This study

^{^a}

All trends reported are statistically significant (P < 0.05). Data from multiple sources are not synchronous; thus we present snapshots of changes over multiple years and regions where data are available.

^{^b}

Trends were calculated for sites with >5 y of measurements by using monthly median concentrations with the requirement that 75% of the month had valid data.

^{^c}

Based on linear regression.

^{^d}

Annual median concentrations.

^{^e}

Monthly median concentrations.

^{^f}

Daily averaged concentrations.

^{^g}

Seasonal Kendall Test and Sen’s slope method.

^{^h}

Stratospheric data and biomass burning plumes filtered based on potential vorticity and CO and ozone concentrations (details provided in methods).

^ⁱ

Trend were calculated for monthly mean wet deposition fluxes of sites with at least 75% data coverage.

^{^j}

Annual wet deposition fluxes are used.

^{^k}

Trends are calculated for sites with >5 y of data and >75% valid data coverage.

^{^l}

Weekly wet deposition fluxes were used.

^{^m}

Trends are calculated for sites with >75% data coverage. Monthly precipitation volume-weighted mean concentrations were used.

^ⁿ

Sites with at least 10 and 7-y data coverage are selected for MDN and EMEP networks, respectively.