Sulfur dioxide (SO2) is one in a group of highly reactive
gasses. Fossil fuel combustion at power plants and other industrial facilities
is one of the largest sources of sulfur dioxide emissions. Extracting metal
from ore and burning of high sulfur containing fuels by locomotives, large
ships, and non-road equipment are some smaller sources of sulfur dioxide
emissions.
Short-term sulfur dioxide exposure may lead to respiratory
effects such as bronchoconstriction and increased asthma symptoms. Children, the
elderly, and asthmatics are three of the most susceptible populations that show
agitation to sulfur dioxide. Sulfur dioxide has the potential to react with
other compounds that are present in the atmosphere to form small particles that
can deeply penetrate into the lungs. This can worsen, or even cause,
respiratory diseases including emphysema and bronchitis. So2 may also irritate
existing heart disease.
Nitrogen dioxide (NO2) is another one in a group of high
reactive gasses. Nitrogen dioxide is released into the air via cars, trucks,
buses, power plants, and off-road equipment. NO2 contributes to the formation
of ground-level ozone and fine particle pollution.
Similar to sulfur dioxide, short term exposure to nitrogen
dioxide is linked to airway inflammation in health populations and increased
respiratory symptoms in populations with asthma. NO2 levels are sometimes 30 to
100% higher in areas within 50 meters of roadways than those areas away from
roadways. Children, the elderly, and those with asthma are susceptible
populations to adverse health effects from nitrogen dioxide exposure.
NO2 may react with ammonia, moisture, and other compounds in
the air to form small particles. These small particles have the potential to
deeply penetrate the lungs and can cause or worsen respiratory diseases such as
emphysema and bronchitis, as well as agitate pre-existing heart disease. Ozone
forms when nitrogen oxide and organic compounds react in the presence of heat
and sunlight. Populations at-risk for adverse health effects when exposed to
ozone include children, the elderly, those with lung diseases, and people who
work or exercise outside. Ozone can cause reduced lung function and increased
respiratory symptoms.
Lichens represent a symbiotic relationship between a fungus
and an algae. Lichens absorb minerals and water, even when there is a low
concentration in the air. Sulfur dioxide and nitrogen dioxide are just two of
the many pollutants that can harm lichens. Airborne compounds such as NO2 cause
lichen substrates to be more alkaline. Lichens in different areas exposed to
different compounds have various tolerances and requirements. If a species such
as Candelaria Concolor or Physica Milegrana is found in an area
that is not naturally nitrogen rich, this is an indicatory that nitrogen deposition
in this area is anthropogenically enhanced. Sulfur dioxide, on the other hand,
disrupts important physiological processes in lichens. Easily absorbed, SO2 has
an acidifying effect on the lichens. Some species are more sensitive than
others, and, therefore, the presence of a sensitive species of lichen means
that sulfur dioxide levels are, more than likely, under the standard level. A “lichen
desert”, an area where there are little to no lichens present, may be the
result of high sulfur dioxide concentrations. These areas are more likely to
have a tolerant species’ growth.
Sources:
