Page 43 - Air pollution and greenhouse gases from basic concepts to engineering applications for air emission control

16 1 Air Emissions

• ozone (O 3 )
• particulate matter (PM)
• carbon monoxide (CO)
• sulfur dioxide (SO 2 )
• nitric oxides (NO x )
• lead (Pb)
These air pollutants are found all over the world and may come from primary
and/or secondary sources. Of the six pollutants, particulate pollution and ground-
level ozone are the most widespread health threats.
The US EPA calls these pollutants criteria air pollutants, because it regulates
them by developing human health and/or environmentally based criteria for setting
permissible levels. The set of limits based on human health is called primary
standards. Secondary standards are another set of limits intended to prevent envi-
ronmental and property damage. The primary standards are aimed at the protection
of the public’s health, and the secondary standards at welfare protection. The US
EPA has set threshold values for six principal pollutants as listed in Table 1.2.
To implement air quality standards, regulators also provide instructions to
quantify the air quality. If the measured pollutant concentrations are less than the
threshold values specified in the standards, the air quality is considered acceptable
in the near future and no action is needed. On the other hand, if the air quality does
not meet the standard, air emissions from some sources have to be reduced in order
to comply with the standards of concern. For example, during the 2008 Summer
Olympics in Beijing, China, air quality in Beijing improved much more than
expected, according to the government official media. Before the Games, it
implemented drastic measures to reduce air pollution by allowing only one-third of
Beijing’s 3.3 million cars on the road on alternate days under an even-odd license
plate system.
Air quality standards are flexible in that they offer governments different
approaches to improving the air quality in a region. They can, however, be complex
and sometimes difficult to enforce, unless there is only one single emission source
in a region. Air quality is usually not a problem in this type of regions, due to the
effective dispersion of the air. When the air quality standard is not met in populated
regions where there are different mobile and stationary sources, it can be difficult to
assign the responsibility, although sometimes it is obvious that automobiles and
large plants are at the root of the problem. To make it more challenging, the
atmosphere itself is responsible for the majority of secondary air pollutants, such as
ground-level ozone and smog, which are the products of many complicated
chemical reactions in the air. Lawyers are likely to make it even more complicated
if there is a court action.