Page 431 - Fundamentals of Air Pollution 3E

I. Changing Times 383

The evolution of our modern society and the concomitant changes in life-
style, workplace, and housing improvements place concerns about indoor
air quality in a different category than for developing countries and from
the times of our ancestors.
For many industrialized countries, efforts to improve the outdoor air
quality have been under way for the majority of this century. In many
locations around the world, significant improvements have taken place.
Air quality in many major cities such as London, New York, and Chicago
has improved from the conditions present in the first half of the twentieth
century. Mechanisms and control programs are in place in the developed
countries to continue the improvement of ambient air quality. Considerable
effort and energy have been expended to characterize, evaluate, and control
air pollution emissions to the atmosphere.
Buildings and their design have undergone major changes. Fifty years
ago, central heating and windows which could be opened and closed de-
pending on the season were the norm for commercial buildings. Now we
have multistory buildings with central heating and air conditioning and
sealed glass exterior walls. Residential housing has undergone similar de-
sign and structural changes, in some cases resulting in dwellings that may
have poorer indoor air quality.
New residences and commercial buildings are designed and built with
energy conservation as a major design criterion. New materials have been
developed and are being used in construction. Although these modifica-
tions have helped save energy, a consequence of some of these modifica-
tions is slower exchange of air with the outside. This helps considerably
with the heating or cooling system because energy must condition this
"new" air which is introduced into the structure.
A second consideration is the change in lifestyle for individuals in indus-
trialized societies. We are no longer a society dependent on occupations
which require us to be outdoors for a significant part of our day. Over the
past two decades, studies of daily activities have consistently shown for
urban populations that, on average, we spend about 90% of our time
indoors in our homes, cars, offices, factories, public buildings such as
restaurants, malls, and others. Any given individual activity profile may
differ significantly from this average.
Exposure assessment techniques now attempt to include as many as
possible of the locations in which individuals now spend time. The concept
involves identification of microenvironments which are important for
potential exposure. For example, exposure to CO would include time
spent in commuting, parking garages, in residences with gas stoves, as
well as time spent outdoors. This approach classifies time spent in these
microenvironments and the typical concentrations of CO in these loca-
tions.