I t is a great honour and joy for me to present this volume of
Scripta Varia which contains the papers presented during the Study Week
on “Chemical Events in the Atmosphere and their Impact on the
Environment” held at the seat of the Academy from the 7th to the 11th
of November, 1983. The discussions which followed each presentation
are included in the volume. These proceedings are of great interest;
they touch on problems which may seem diverse for a non-knowledgeable
person, or insignificant to those who flee the reality of our present world.
Environmental pollution has played a critical role in human lives since
the early history of the nomadic tribes. During the last millennium,
industrial revolution, increased population growth and urbanization have
been the major determinants in shaping our environmental quality.
Initially primary air pollutants such as sulfur dioxide and particulate
matter were of concern. For example, the killer fog of London in 1952
resulted in significant numbers of human fatality leading to major air
pollution control measures....
Kanchha’s father immediately found a job in a brick kiln factory not very far from the
city. These kilns produce highly concentrated amounts of fine particulate matter,
which interact with other industrial and vehicle fumes over Kathmandu. Brick
kilns use coal as their main fuel source, and this contributes to the air pollution in
Kathmandu by pumping considerable quantities of sulfur dioxide (SO2) and other
toxic substances into the atmosphere. After a few months, Kanchha’s father started
Sulfur trioxide irritates the mucous membranes of the respiratory tract. A concentration of 1
volume of SO3 in a million volumes of air (one part per million or 1 ppm) is enough to
cause coughing and choking. Sulfur trioxide dissolves in water to form sulfuric acid,
which is a strong acid capable of corroding or destroying many materials. Sulfur trioxide
can absorb moisture from the atmosphere to form very fine droplets of sulfuric acid.
Inhalation of these droplets can harm the respiratory system. Chronic exposure leads to a
much greater likelihood of suffering from bronchitis.
Unlike ozone, which has a specific chemical composition, airborne particles vary in size
and composition depending on time and location. Although the components of particles
may have common sources, the types and amounts of particles collected at any one
time and location may be unique.
To add to the problem, gaseous pollutants including ozone, sulfur dioxide, nitrogen
dioxide and carbon monoxide often are present in the atmosphere at the same time as
These efforts have attenuated the emissions engendered by growth, but 24-hour PM10
(particulate matter with aerodynamic diameter less than 10 m) concentrations exceeding
several hundred µg/m3
are still measured at many monitoring sites.
A persistent haze
blankets the city, especially during winter, and there is great concern among residents and
visitors about the effects of suspended particles on health. Aerosols that contribute to this
visibility degradation are usually a combination of primary and secondary particles.
Biological nitrogen fixation is a vital process in the global nitrogen
cycle, transforming dinitrogen in the atmosphere into ammonia.
Being a very energy-demanding and oxygen-sensitive process, both
expression and activity of the nitrogenase enzyme are tightly regu-lated. Rhodospirillum rubrumis a free-living, photosynthetic, purple
non-sulfur nitrogen-fixing bacterium, which has been extensively
used as a model organism for metabolic and regulatory studies
regarding nitrogen fixation.