"Primary ambient air quality standards" or "primary standards"
mean levels established to protect the public health from adverse
effects. The adverse effects that the standards should protect
against include acute or chronic subjective symptoms and
physiological changes that are likely to interfere with normal
activity in healthy or sensitive individuals or to interfere
unreasonably with the enjoyment of life or property. (From MN
Rule 7009.0010)

CAS Number: 7439-96-5. A gray-white metal, resembling iron, but
is harder and very brittle. It is reactive chemically, and
decomposes in cold water slowly. Manganese is used to form many
important alloys. In steel, manganese improves rolling and
forging qualities, strength, toughness, stiffness, wear
resistance, and hardness. Manganese colors glass an amethyst
color, and is responsible for the color of true amethyst.
Chemical formula = Mn. Molecular weight = 54.938 g/mol.

CAS Number: 7440-74-6. Indium is a very soft, silvery-white metal
with a brilliant lustre. The pure metal gives a high-pitched
"scream" when bent. It is useful for making low-melting alloys.
When plated or evaporated onto glass, it forms a mirror as good
as that formed by silver, but with superior resistance to
atmospheric corrosion. Indium is a byproduct of the formation of
lead and zinc. Indium metal is isolated by the electrolysis of
indium salts in water. Chemical formula = In. Molecular weight =
114.82 g/mol.

CAS Number: 7440-55-3. Gallium is the only metal, except for
mercury, caesium, and rubidium, which can be liquid near room
temperatures, which makes possible its use in high-temperature
thermometers. Ultra-pure gallium has a beautiful, silvery
appearance. Gallium compounds are also used to create
semiconductors and microwave equipment. Chemical formula = Ga.
Molecular weight = 69.72 g/mol.

CAS Number: 7440-50-8. Copper is a reddish metal that occurs
naturally in rocks, soil, water, and air. It also occurs
naturally in plants and animals. Metallic copper is easily molded
or shaped, and can be found in the U.S. penny, electrical wiring,
and some water pipes. It can also be found in mixtures (called
alloys) with other metals such as brass and bronze. Copper is
also found as part of other compounds forming salts. Copper salts
occur naturally, but are also manufactured. The most common

CAS Number: 7440-48-4. Cobalt is a naturally occurring element
found in rocks, soil, water, plants, and animals. There are non
radioactive and radioactive forms of cobalt. Non-radioactive
cobalt, referred to as stable cobalt, is used to produce metal
alloys used in the manufacture of aircraft engines, magnets,
grinding and cutting tools, artificial hip and knee joints.
Cobalt compounds are also used to color glass, ceramics and
paints, and used as a drier for porcelein enamel and paints.

Bromine is the only liquid nonmetallic element. It is a heavy,
volatile, mobile, dangerous reddish-brown liquid. The red vapor
has a strong unpleasant odor and the vapor irritates the eyes and
throat. It causes severe burns upon contact with the skin. In
concetrated form, it is a serious health hazard, and maximum
safety precautions should be taken when handling it. Bromine is
used in agricultural chemicals, dyestuffs, chemical intermediates
and flame-retardants. Most is used to prepare 1,2-dibromoethane,

CAS Number: 7440-41-7. Beryllium is a hard, grayish metal
naturally found in mineral rocks, coal, soil, and volcanic dust.
Beryllium compounds are commercially mined, and the beryllium is
purified for use in nuclear weapons and reactors, aircraft and
space vehicle structures, instruments, x-ray machines, and
mirrors. Beryllium ores are used to make speciality ceramics for
electrical and high-technology applications. Beryllium alloys are
used in automobiles, computers, sports equipment (golf clubs and

CAS Number: 7440-39-3. A silvery-white metal found in nature.
Barium enters the environment during the mining, refining, and
production of barium compounds, and from the burning of coal and
oil. Barium compounds are used by the oil and gas industries to
make drilling muds. Barium sulfate is sometimes used by doctors
to perform medical tests and to take barium-rays of the stomach.
Chemical formula = Ba. Molecular weight = 137.34 g/mol.

CAS Number: 7758-97-6. A yellow solid that is used to produce
dyes, inks, paints and plastics. Chemical formula = PbCrO4.
Molecular weight = 323.2 g/mol.