Environmental Engineering Reference
In-Depth Information
Volatile organic compounds
VOCs are gases emitted from a variety of solid or liquid sources with short- and long-term
impact on human health and the environment. The number of compounds that fall into this
category is in the thousands.
Very often, VOCs are responsible for indoor air quality. Some examples are paints, lacquers,
paint strippers, cleaning supplies, pesticides, building materials, furnishings, office equipment,
such as copiers and printers, correction fluids, carbonless copy paper, graphics and craft mate-
rials including glues and adhesives, permanent markers, dry cleaning agents, and photographic
solutions (Gustin, 2003; “An introduction to indoor air quality,” n.d.). In outdoor emission of
VOCs, methane is probably the most abundant from both biogenic and anthropogenic sources;
however, for the purpose of inventories, methane is considered a GHG and excluded from the
list of VOCs. Examples of other industrial and nonindustrial VOCs are the products of fuel
combustion, hydraulic fluids, and lubricant oils.
The food-processing industry is responsible for the emission of an important array of
VOCs (Table 8.2). Emissions come from processing operations such as fermentation,
baking, roasting, frying, animal rendering, coffee production, vegetable oil extraction, as
well as cleaning and sanitation chemicals (“Volatile organic compound [VOC] control in
the food processing industry,” 1996). Compounds of interest include alcohols, aldehydes,
oils, chlorinated compounds, and mercaptans. Other VOCs are contained in certain food
products and released during processing. An example is the extraction of citrus juices in
which terpenes contained in citrus oil are emitted during expression and further processing
of the spent peels. Even when processors do their best to recover these compounds, because
they have an economic value, the technology is not 100-percent effective and air emissions
occur as a result.
Ammonia emissions
In the food supply chain, the largest ammonia emissions take place at agricultural fields
from nitrogen fertilization and from manure at animal husbandry operations (see Chapter 3).
Another source of ammonia emissions are food-processing plants, where ammonia is used
in refrigeration equipments and can be occasionally released due to leaks or vented by high
pressure valves.
In the United States, agriculture is responsible for 90 percent of ammonia emissions.
About 80 percent is direct emissions from animal production and 10 percent from fertilizer
application (Figure 8.1).
Ammonia has many negative impacts on the environment. The deposit of atmospheric
ammonia on land and water where nitrogen is limited causes nutrient enrichment and alteration
of the balance of terrestrial and aquatic ecosystems. In soils with low buffering capacity, the
oxidation of ammonia to nitrate by bacteria produces acidification of soil that affects many
plant species. Ammonia reacts with sulfate and nitrate ions and forms ammonium sulfate and
ammonium nitrate, which then nucleates into fine and ultrafine particle matter, PM
2.5
. These
particles cause human toxicity, and when suspended in the air, contribute to regional haze.
Ground-level ozone
Ozone in the stratosphere (upper atmosphere) is a beneficial gas that shields the earth from
harmful ultraviolet-b rays. However, when ozone develops in the lower atmosphere, it is
considered an environmental pollutant. Ground-level ozone, also known as tropospheric
