Basics and Discovery of Atmospheric Chemicals - Air Pollution and Global Warming: History, Science, and Solutions - page 3

cloud drops, ice crystals, raindrops, snowflakes, and
hailstones. The main difference between an aerosol par-
ticle and a hydrometeor particle is that the latter contains
much more water than the former.
Liquids in aerosol particles and hydrometeor parti-
cles may be pure or may consist of a solution. A solu-
tion is a homogeneous mixture of substances that can
be separated into individual components on a change of
state (e.g., freezing). A solution consists of a solvent ,
such as water, and one or more solutes dissolved in the
solvent. Solids may be mixed throughout a solution but
are not part of the solution. In this text, pure water and
solutes dissolved in water are denoted with “(aq)” for
aqueous (dissolved in water). Gases are denoted with
“(g)”, and solids are denoted with “(s)”.
Gases and aerosol particles may be emitted into the
air naturally or anthropogenically or formed chemi-
cally in the air. Anthropogenic emissions are human-
produced emissions, such as from fossil fuel com-
bustion or industrial burning. Hydrometeor particles
generally form from physical processes in the air. Air
pollution occurs when gases or aerosol particles, emit-
ted anthropogenically, build up in concentration suf-
ficiently high to cause direct or indirect damage to
humans, plants, animals, other life forms, ecosystems,
structures, or works ofart.

were aware of these metals. Of note were the Chaldeans
(612-539 BC), who connected them with planets, iden-
tifying gold as the sun, silver as the moon, lead as
Saturn, mercury as Mercury, iron as Mars, copper as
Venus, and tin as Jupiter. Of these seven metals, lead,
mercury, and iron are the most relevant to air pollution
today.

1.2.1.1. Lead
Lead ( plumbum in Latin) is a dense bluish-white metal
element. It was discovered before 6400 BC in modern-
day Turkey, probably during the heating of lead ore
(lead bound with sulfur, copper, zinc, or silver) in a
campfire. Lead melts at a temperature of 327 ◦ C. In
afire, lead liquefies, separating from its ore. Because
it is so dense (11.3 times the density of water), pure
lead would flow to the bottom of a campfire. Because
resolidified lead is malleable (Figure 1.2), early users
of lead molded it in into cookware and jewelry. The
Romans molded it into pipes.
Lead was referred to in the Books of Job and Num-
bers as biblicalx .The Roman Pliny the Elder (23-79
AD) called it plumbum nigrum , and the English word
plumber describes a person who installs or fixes lead

1.2. History of Discovery of Elements and
Compounds of Atmospheric Importance
Reactive elements that comprise most gases in the air
are hydrogen (H), carbon (C), nitrogen (N), oxygen
(O), fluorine (F), sulfur (S), chlorine (Cl), and bromine
(Br). Unreactive elements in the air include helium
(He), argon (Ar), krypton (Kr), neon (Ne), and xenon
(Xe). Two radioactive elements of importance are polo-
nium (Po) and radon (Rn). Aerosol particles contain the
elements present in gases and often sodium (Na), mag-
nesium (Mg), aluminum (Al), silicon (Si), potassium
(K), calcium (Ca), iron (Fe), lead (Pb), and/or phos-
phorus (P). Tables 1.2 and 1.3 summarize the dates of
discovery of elements and compounds, respectively, of
atmospheric importance.

1.2.1. Solids and Liquids,
Ancient World-1690
The first elements in the periodic table to be identified
were the metals gold (Au), silver (Ag), lead (Pb), mer-
cury (Hg), iron (Fe), copper (Cu), and tin (Sn). Many
cultures, including the Egyptians and the Chaldeans,

Figure 1.2. Melted and shaped lead. C Shootzpics/

Dreamstime.com.