write:As humans evolved the atmosphere began to be affected by human activities. Initially these effects were small and insignificant. With the enormous growth in human numbers resour

geogenic
and atmospheric processes. As humans evolved
the atmosphere began to be affected by human activities. Initially
these effects were small and insignificant. With the enormous growth in human numbers
resource use
and technological advancements
the impact of humans on the atmosphere has been and continues to be significant. We generally view (in the absence of human activity) the atmosphere and other environmental media
such as water and land
to be “clean.” On contamination with our “wastes
” they become “polluted.” The concept of pollution includes a sense of degradation
a loss of quality
a departure from purity
and adverse environmental effects. Air becomes polluted when it is changed by the introduction of gas- or particulate-phase substances or energy forms (heat
noise
radioactivity) so that the locally
regionally
or globally altered atmosphere poses harm to humans
biological systems
materials
or the atmosphere itself. Air pollution concerns
historically
have focused on the freely moving air of the outdoor environment described as ambient air. It is pollution of the ambient air that is the primary focus of regulatory programs
as well as this book. However
it is but one of several air pollution or air quality concerns. Significant air pollutant exposures occur in industrial workplaces and the built environments of our homes
offices
and industrial buildings
and from personal habits such as smoking. 2.1 NATURAL AIR POLLUTION Contamination or pollution of the atmosphere occurs as a consequence of natural processes as well as human activity (the latter are called anthropogenic). Though regulatory programs focus exclusively on anthropogenic air pollution
it is important to understand that nature contributes to atmospheric pollution and
in some instances
causes significant air quality problems. As evidenced by volcanic activity in the 19th century (e.g.
Tambora and Krakatoa) and the more recent eruptions of Mt. St. Helens in Washington State
El Chinchon in Mexico
and Mt. Pinatubo in the Philippines
as well as the 1988 forest fires in Yellowstone National Park and the western U.S.
pollutants produced naturally can have significant effects on regional and global air quality. In addition to volcanoes and forest fires
natural air pollution occurs from a variety of sources: plant and animal decomposition
pollen and spores
volatile hydrocarbons (HCs) emitted by vegetation
ocean spray
soil erosion and mineral weathering by wind
emission of gasphase substances from soil and water surfaces
ozone (O3) and nitrogen oxides (NOx) from electrical storms
and O3 from stratospheric intrusion and