In-depth review of atmospheric mercury: sources, transformations, and potential sinks

Figures & data

Figure 1 Vapor pressure of elemental mercury as a function of temperature.

Notes: 1 Pascal =9.87×10⁻⁶ atmospheres. Data from Huber et al.⁴

Figure 2 Solubility of elemental mercury in water as a function of temperature.

Note: Data from Glew and Hames.⁶

Figure 3 Henry’s law constant as a function of temperature for elemental mercury in water.

Notes: Henry’s law constant: K_H (atm-m³/mol) = P_Hg (atm)/c_aq(mol/m³). Data from Glew and Hames.⁶

Table 1 Physical and chemical properties of mercury and some of its compounds at 20°C–25°C

Name	Molecular formula	Structure weight	Molecular solubility	Water constant	Henry’s law
Mercury	Hg	–	200.59	61 μg/L	8.7×10^-3
Mercury(I) chloride	Hg2Cl2	Cl-Hg-Hg-Cl	472.09	4.0 mg/L	–
Mercury(I) bromide	Hg2Br2	Br-Hg-Hg-Br	560.99	22 μg/L	–
Mercury(I) iodide	Hg2I2	I-Hg-Hg-I	654.99	0.24 μg/L	–
Mercury(I) oxylate	Hg2C2O4	[2Hg]^2+[O2-C-C-O2]^2–	489.20	3.5 μg/L	–
Mercury(II) chloride	HgCl2	Cl-Hg-Cl	271.52	73 g/L	7.1 × 10–^10
Mercury(II) bromide	HgBr2	Br-Hg-Br	360.40	6.1 g/L	–
Mercury(II) iodide	Hgl2	l-Hg-l	454.40	0.14 μg/L	–
Mercury(II) oxalate	HgC2O4	[Hg]^2+[O2-C-C-O2]^2-	288.61	0.4 g/L	1.4×10^-9
Mercury(II) oxide	HgO	Hg-O	216.59	53 mg/L	7.1×10–^7
Methylmercury chloride	CH3HgCl	CH3-Hg-Cl	251.10	0.1 g/L	4.7×10–^7
Dimethylmercury	C2H6Hg	CH3-Hg-CH3	230.66	1 g/L	7.6×10–^3

Notes: Henry’s law constant, expressed as the ratio of the partial pressure above the solution to the solution concentration (K_H = P_Hg/c_aq), at 25°C, is given in atm-m³/mol. Data from: Clever et al,⁸ Dry and Gledhill,¹¹ National Research Council,¹² Iverfeldt and Lindqvist,¹³ and Sillman et al.¹⁴

Table 2 Stability constants for complexes formed by mercury(I) and mercury(II) in aqueous solution at 25°C

Ligand	Name	logK (Hg2^2+)	logK (Hg^2+)
SO4^2–	Sulfate	3.5	1.3
P2O7^4–	Pyrophosphate	15.6	17.5
H3COO–	Acetate	–	23.2
HCOO–	Formate	–	9.6
OOC-COO^2–	Oxalate	13.0	–
OOC(CH3)2COO^2–	Succinate	13.5	–
OOCC6 H4 COO^2^–	Phthalate	4.9	–
C6H5NH2	Aniline	3.7	4.6
NH2CH2COOH	Glycine	–	10.3
HSCH2CH(NH2)	Cysteine	–	14.4
COOH
HSC6 H4 COOH	Thioglycolic acid	–	34.5

Note: Data from: Chipperfield,¹⁵ Yamane and Davidson,¹⁶ Wirth and Davidson,¹⁷ and Ravichandran.¹⁹

Figure 4 Methylation of mercury by methylcobalamine, a form of vitamin B₁₂, to form the methylmercuric cation.

Note: Data from Weber.²²

Figure 5 Mercury concentrations measured in ice cores obtained from the Upper Fremont Glacier in the Wind River Mountain Range of Wyoming.

Notes: Preindustrial background concentrations indicated with green line. Volcanic emissions indicated by blue text. Data from Schuster et al,³² and Schuster PF et al. 2002, Fremont Glacier Atmospheric Mercury Data, IGBP PAGES/World Data Center for Paleoclimatology. Data Contribution Series # 2002-038. NOAA/NGDC Paleoclimatology Program, Boulder, CO, USA.³³
Abbreviation: WWII, World War II.

Figure 6 Relative contributions of estimated mercury emissions to the atmosphere from natural sources.

Note: Data from Varekamp and Buseck.⁴⁴

Figure 7 Relative contributions of estimated mercury emissions to the atmosphere from current anthropogenic sources.

Note: Data from Varekamp and Buseck.⁴⁴

Table 3 Distribution of current anthropogenic mercury emissions to the atmosphere by region

Region	Emissions (tonnes per year)	Range (tonnes per year)	% of total
Australia, New Zealand, Oceania	22.3	5.4–52.7	1.1
Central America, Caribbean	47.2	19.7–97.4	2.4
East/Southeast Asia	777	395–1,960	39.7
European Union	87.5	44.5–226	4.5
Middle Eastern States	37.0	16.1–106	1.9
North Africa	13.6	4.8–41.2	0.7
North America	60.7	34.3–139	3.1
Russian Commonwealth	115	42.6–289	5.9
South America	245	128–465	12.5
South Asia	154	78.2–358	7.9
Sub-Saharan Africa	316	168–514	16.1
Undefined	82.5	70.0–95.0	4.2
Total	1,960	1,010–4,070	100

Notes: Undefined represents estimated emissions from contaminated sites. Data from Varekamp and Buseck.⁴⁴

Figure 8 Relative contributions of estimated mercury emissions to the atmosphere from historical anthropogenic sources.

Note: Data from Friedli et al.⁵⁵

Table 4 Speciation of mercury emissions from different sources given as percent of total emissions

Source	Hg^0	Gas phase Hg^2+	Particulate Hg^2+
Coal combustion	50	40	10
Coal-cement kilns	80	15	5
Mining and smelting	80	15	5
Chlor-alkali	70	30	0
Waste incineration	20	60	20
Cremation	80	15	5
Artisan gold mining	100	0	0
Oceans	100	0	0
Soil	100	0	0
Biomass burning	95	0	5
Geothermal	100	0	0
Volcanic	94	1	5

Note: Data from: the Arctic Monitoring and Assessment Programme, United Nations Environmental Programme;⁵³ and Friedli et al.⁵⁴

Table 5 Important reactions of mercury relevant to the atmosphere with overall rate constants and atmospheric mercury lifetimes estimated from reaction kinetics

Gas phase reactions	Rate constants (cm^3 molec^-1 sec^-1)	Lifetimes
1. Hg^0 + O3 → HgO + O2	3×10–^20	1.4 years
2. Hg^0 + OH → HgOH	6×10–^19	25 days
HgOH + O2 → HgO + OH	9×10–^14	8 months
3. Hg^0 + H2O2→ Hg^2+	<8×10–^19	> 1.5 years
4. Hg^0 + Cl2 → HgCl2	2×10–^18	50 years
5. Hg^0 + Br2 → HgBr2	<9×10–^17	> 5 days
6. Hg^0 + Cl → HgCl	1×10–^11	3–4 months
7. Hg^0 + Br → HgBr  HgBr → Hg + Br  HgBr + Br → HgBr2  HgBr + OH → HgBr(OH)	3×10–^12	9 hours
	8×10–^3
	2×10–^10
	2×10–^1
8. Hg^0 + BrO → HgBrO	1×10–^14	12 hours
Aqueous phase reactions	Rate constants (M–^1 sec–^1)
9. Hg^0 + O3 → Hg^2+ + OH– + O2	5×10^7
10. Hg^0 + OH → Hg^2+	2×10^9
11. Hg^0 + HOCl → Hg^2+ + Cl + OH–	2×10^6
12. Hg^0 + OCl– → Hg^2+ + Cl + OH–	2×10^6
13. Hg^0 + Br2 → Hg^2+ + 2Br–	2×10–^1
14. Hg^0 + HOBr → Hg^2+ + Br + OH–	3×10–^1
15. Hg^0 + OBr– → Hg^2+ + Br + OH–	3×10–^1
16. Hg^+2 + HO2 → Hg^0	2×10^4
17. Hg(OH)2 + hv→ Hg^0	3×10–^7
18. HgSO3 → Hg^0 + S(IV) –	< 1 × 10–^4
19. H(SO3)^2– → Hg^0 + S(IV)	5×10^3
20. Hg(COO)2R → Hg^0 + RCOO–^2	1×10^4

Note: Data from: the Arctic Monitoring and Assessment Programme, United Nations Environmental Programme;⁵³ and Liu et al.⁶¹

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