the most abundant gaseous pollutant; results from burning coal and oil. SO2 can be a respiratory irritant. It is one of the major components of acid rain.

Merriam-Webster Online Dictionary
sulfur dioxide (noun)
a heavy pungent toxic gas SO that is easily condensed to a colorless liquid, is used especially in making sulfuric acid, in bleaching, as a preservative, and as a refrigerant, and is a major air pollutant especially in industrial areas - 2
sulfur dioxide (Wikipedia)
Sulfur dioxide
Skeletal formula sulfur dioxide with assorted dimensions
Spacefill model of sulfur dioxide
The Lewis structure of sulfur dioxide (SO2), showing unshared electron pairs.
Names
IUPAC name
Sulfur dioxide
Other names
Sulfurous anhydride
Sulfur(IV) oxide
Identifiers
3D model (JSmol)
3535237
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.028.359
EC Number 231-195-2
E number E220 (preservatives)
1443
KEGG
MeSH Sulfur+dioxide
RTECS number WS4550000
UNII
UN number 1079, 2037
Properties
SO
2
Molar mass 64.066 g mol−1
Appearance Colorless gas
Odor Pungent; similar to a just-struck match
Density 2.6288 kg m−3
Melting point −72 °C; −98 °F; 201 K
Boiling point −10 °C (14 °F; 263 K)
94 g/L
forms sulfurous acid
Vapor pressure 237.2 kPa
Acidity (pKa) 1.81
Basicity (pKb) 12.19
−18.2·10−6 cm3/mol
Viscosity 0.403 cP (at 0 °C)
Structure
C2v
Digonal
Dihedral
1.62 D
Thermochemistry
248.223 J K−1 mol−1
−296.81 kJ mol−1
Hazards
GHS pictograms GHS05: Corrosive GHS06: Toxic
GHS signal word Danger
H314, H331
NFPA 704
Flammability code 0: Will not burn. E.g., waterHealth code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gasReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogenSpecial hazards (white): no codeNFPA 704 four-colored diamond
0
3
0
Lethal dose or concentration (LD, LC):
3000 ppm (mouse, 30 min)
2520 ppm (rat, 1 hr)
993 ppm (rat, 20 min)
611 ppm (rat, 5 hr)
764 ppm (mouse, 20 min)
1000 ppm (human, 10 min)
3000 ppm (human, 5 min)
US health exposure limits (NIOSH):
PEL (Permissible)
TWA 5 ppm (13 mg/m3)
REL (Recommended)
TWA 2 ppm (5 mg/m3) ST 5 ppm (13 mg/m3)
IDLH (Immediate danger)
100 ppm
Related compounds
Related sulfur oxides
Sulfur monoxide
Sulfur trioxide
Related compounds
Ozone

Selenium dioxide
Sulfurous acid
Tellurium dioxide

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Sulfur dioxide (also sulphur dioxide in British English) is the chemical compound with the formula SO
2
. It is a toxic gas responsible for the smell of burnt matches. It is released naturally by volcanic activity and is produced as a by-product of the burning of fossil fuels contaminated with sulfur compounds and copper extraction.

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