Page 42 - Air pollution and greenhouse gases from basic concepts to engineering applications for air emission control

1.5 General Approaches to Air Emission Control 15

One approach to the lowest emission level is the employment of the best
technologies currently available to keep the equipment in a good operating con-
dition. The corresponding regulations (or standards) have to specify the “best
technology” equipment. Since the best technology currently available allows for the
lowest emissions currently possible, the corresponding standard does not have to
specify the emission rate from a facility or equipment installed with such devices.
This “best technology” approach is a good application where accurate emission
monitoring is challenging. For example, US state regulations for large underground
storage tanks (UST) require the operators to install the best floating roofs available
and the equipment has to be well maintained. Another example is the prohibition of
manure spread in many local municipalities to minimize the odor dispersion to local
communities. It is sometimes economically challenging for industry to keep up with
advances in technology. Replacement of the entire air pollution control system of a
power plant is not as easy as changing the diesel particulate filter under a truck.
Another approach to air emission standards does not require an operator to
install the best technology; it is up to the operator to decide. The regulations set the
maximum air emission rates for different air pollutants.
It is simple, but expensive, to implement air emission standards. In these stan-
dards, permitted emission rates and the standard test procedures are clearly
described. Any trained professional can follow the standard procedure to determine
whether the standards are met at a facility. As the best technology approach is
generally expensive, it may not be always necessary to implement this standard for
facilities in remote areas with low populations.
The flexibility of air emission standards is poor. It is impractical to shut down a
utility plant that supplies electricity or heat to a large community, even if it cannot
meet the local air emission standard. In this case, it is obvious that air emission
standards may fail to control air pollution. Compared to air emission standards, air
quality standards are much more flexible in addressing this political challenge.

1.5.1.2 Air Quality Standards

Air quality standards are developed based on extensive scientific study on and
validation of the threshold values of the air pollutants. Due to the nature of scientific
research, statistical errors are allowed. One well-known example of air quality
standards is the US National Ambient Air Quality Standards (NAAQS), which have
established limitations on air pollutants considered harmful to public health and the
environment (with details available at http://www.epa.gov/air/criteria.html). These
standards vary with location, time, and sector and they are subject to regular
reviews and revisions, as needed.
Not all air pollutants are regulated by air quality standards. The US Clean Air
Act requires the Environmental Protection Agency (EPA) to set National Ambient
Air Quality Standards for six criteria air pollutants: