Environmental Engineering Reference
In-Depth Information
On average for air transportation mode, specific carbon emissions for short and long hauls
are around 1,400 and 800 grams of carbon dioxide/tonne km, respectively (Table 13.5). In
addition, there are emissions from ground support equipment, such as ground power units, tow
tractors, air start units, and refueling and de-icing trucks.
Like any other internal combustion engines burning carbon containing fuel, jet engines
produce emissions of pollutants that includes volatile organic compounds (VOCs), carbon
monoxide (CO), nitrogen oxides (NOx), sulfur dioxide (SO
2
), and particle matter. For the year
2002 global average values in terms of grams of pollutant per kg of fuel burned were 1.5, 5.3,
13.2, and 0.6, for VOCs, CO, NOx, and SO
2
, respectively (ICF, 2005). According to Tesseraux
(2004), 356 organic compounds (VOCs) are present in the exhaust of jet engines run at aver-
age load, but only 103 have been identified and quantified. Some of the compounds found
were normal alkanes ranging from 1 to 17 carbons, cyclic alkanes, benzene, toluene, ethylb-
enzene, xylene, styrene, phenol, formaldehyde, acetaldehyde, and acrolein. Some of the VOCs
are emitted as gas; and many, similarly to the case of diesel engines, are found adsorbed on the
surface of particle matter.
Sulfur emissions depend on the amount of sulfur compounds in the fuel. Over 90 percent
of sulfur is oxidized into gaseous sulfur dioxide and the rest is transformed into sulfate com-
pounds and emitted as particle matter (Wayson et al., 2009).
Refrigerated transport
In addition to the emissions from the transporting vehicle, refrigerated transport generates two
types of emissions: from energy consumption to produce low temperatures and from refriger-
ant leaks.
On board refrigeration equipment generates direct emissions from diesel engines that power
refrigeration equipment or indirect air emissions from electricity generation to feed reefers
equipped with electric motors. See Chapter 11 for more on direct and indirect emissions.
Impact from refrigerant escape
Transport refrigeration equipment is subjected to harsh working conditions, such as
extreme heat and cold, vibration, corrosion, and impact forces, which make them vulner-
able to refrigerant leaks. The substitution of porthole reefers with integral units makes
operability easier, but increases the changes of leaks by multiplying the number of refrig-
eration units.
Concerns about refrigerant leaks started when it was discovered a positive correlation
between the release of chlorinated compounds, such as CFCs (chlorofluorocarbons) and
HCFCs (hydrochlorofluorocarbons), into the atmosphere and the destruction of strato-
spheric ozone, which is responsible for protecting the Earth from exposure to UV rays. As
a consequence, the production of these compounds was banned worldwide and replaced
by hydrofluorocarbons (HFCs). Unfortunately, if was quickly discovered that although
HFCs do not affect the stratospheric ozone, they have an extremely high global warming
potential.
Even though CFCs and HCFCs have been banned from production, they are still in used in
old refrigeration equipment including transport refrigeration. The plan is to replace all the
chlorine-containing refrigerants with HFCs and eliminate the stockpile of chlorinated gases;
however, these actions will not eliminate the needs for leak prevention and avoidance due to
the global warming effect of HFCs. See Chapter 8 for more on this topic.
