- (E) Nitrous oxide is emitted by bacteria in soils and oceans and has 300
times more impact as a greenhouse gas than carbon dioxide. Nitrous oxide is
the fourth largest contributor to greenhouse gases ranked behind water
vapor, carbon dioxide, and methane.
Radon (Rn) is a radioactive element and occurs naturally as the decay
product of uranium and thorium. Radon sticks to dust particles in the air. If
contaminated dust is inhaled, these particles can stick to the airways of the
lung and increase the risk of developing lung cancer. Radon is responsible
for the majority of the public exposure to radiation. Radon gas from natural
sources can accumulate in buildings, especially in confined areas such as
attics and basements. According to the Environmental Protection Agency
(EPA), radon is the second most frequent cause of lung cancer, after
cigarette smoking, causing 21,000 lung cancer deaths per year in the United
States.
Sulfur dioxide (SO 2 ) is a poisonous gas with a pungent, irritating smell
that is naturally released by volcanoes. Further oxidation of SO 2 , usually in
the presence of a catalyst such as NO 2 , forms H 2 SO 4 , and thus acid rain.
Sulfur dioxide emissions are also a precursor to particulates in the
atmosphere.
Formaldehyde (CH 2 O) is found in plants, fruits, vegetables, animals
(including humans), and seafood. The highest concentrations of
formaldehyde are found in dried shiitake mushrooms (up to 400 mg
formaldehyde per kg of mushroom). Formaldehyde is essential in human
metabolism and is required for the synthesis of DNA and amino acids.
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