Short-term exposure to SOx according to EPA's website can cause many different respiratory effects such as: increased asthma symptoms, or bronchoconstriction. The short term is classified as 5 minutes to 24 hours. Effects from exposure may increase greatly with exercise. Short term exposure correlates with increased hospital visits due to respiratory problems. SOx can also react with other components in the air which can travel deeper into the lungs and create or worsen emphysema and bronchitis and cause premature death. The main source of SOx is from fuel combustion, other minor sources are from industrial processes, fires and mobile sources.
Short term effects from NOx can cause airway inflammation in healthy people, and increased symptoms of people with asthma. Short term exposure is defined as 30 minutes to 24 hours. As with SOx NOx is also shown to cause increased hospital visits. The main source of NOx is from mobile, other minor sources are from fuel combustion, industrial processes, and biogenics. Areas near highways have 30-100% more NOx than areas away from roadways. Unfortunately over 15% of the population lives 300 feet or less away from a highway which increases their exposure to NOx. NOx can react with other particles in the air and penetrate deep into the lungs to create such as emphysema and bronchitis, and can aggravate existing heart disease, leading to increased hospital admissions and premature death.Ozone can also be created from the reaction of the combination of NOx, sunlight, and volatile compounds.
Lichens are commonly used as biomonitors of air quality. Lichen growth patterns change as pollution-sensitive species are replaced by pollution tolerant species. For this reason, those species known to be especially sensitive or tolerant can be used as bioindicators of atmospheric quality. Some examples of the effects of high levels of pollution on lichen include reduced photosynthesis, bleaching and death of the photosynthetic partner, and discoloration and reduced growth of the lichen fungus. Many species are sensitive to even moderate levels of SO2 pollution and rapidly disappear from polluted habitats. Especially sensitive or tolerant species are referred to as "indicator species" because their presence or absences can be a relatively accurate predictor of the air quality.
Candelaria concolor is a lichen species that are pollutant tolerant, or a species that generally respond positively to a wide range of pollutants. Areas near lots of mobile sources had an abundance of Candelaria concolor or other pollutant tolerant lichen species. Exposure to NOx and SOx will cause Candelaria concolor to bloom more rapidly.
Physcia millegrana is known as a nitrophile. These species thrive in nutrient-enriched areas receiving N inputs from fertilizer application in agricultural areas or N emissions from power plants, automobile exhaust or industry. Physcia milegrana is affected by NOx positively and causes blooms of it to occur in areas with lots of NOx pollution.
http://www.nps.gov/prwi/learn/nature/upload/Lawrey_2011_Lichen_Bioindicators_Final_Report-1.pdf
http://www3.epa.gov/airquality/sulfurdioxide/health.html
http://www3.epa.gov/airquality/nitrogenoxides/health.html
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