Global Air Pollution
Air pollution respects no borders. It mixes with the air and becomes highly mobile, contaminating ecosystems thousands of kilometres away from the source of the pollution. There are many treaties and conventions attempting to restrict the worst types of pollution, but many problems still remain. The consequences of global air pollution include ozone hole depletion and climate change.
The Stockholm Convention (2001) on Persistent Organic Pollutants is concerned with the elimination or restriction of POPs. It is one of the three principal instruments in the UN hazardous waste management arsenal.
There were 179 parties to the Stockholm Convention by 2013, which include 178 states and the European Union. As usual, the United States is obstructing global concensus, and has not ratified. Other non-ratifying states include Israel, Malaysia, Italy and Iraq.
Together, the three global conventions of the UNO, Basel, Stockholm and Rotterdam, target the most dangerous chemical pollutants like dioxins and furans, hazardous pesticides and DDT, polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), PFOS, and the heavy metals: arsenic, cadmium, mercury and lead, and more chemicals are added at regular meetings (COP).
Polyaromatic hydrocarbons (also polycyclic aromatic hydrocarbons), PAH, are compounds consisting only of carbon and hydrogen, forming a number of aromatic rings. PAHs are persistent pollutants, bioaccumulate, and are harmful to humans. They can be transported through water and air.
Aromatic rings are hexagons of carbon atoms with non-localised hydrogen atoms. PAHs are created by incomplete combustion of organic matter, and in natural processes, such as during the formation of fossil fuels, where there is a lack of oxygen.
Examples are two-ring naphthalene, and three-ring anthracene and phenanthrene. Four-ring: tetracene, chrysene, triphenylene, pyrene, benzofluorene. Five-ring: pentacene, benzopyrene, corannulene. Six-ring: benzoperylene, coronene. Eight-ring: ovalene.
PAHs are pollutants, persistent in the environment, and hazardous to human health. For example, the benzopyrene class is mutagenic and very carcinogenic. They also cause cardiovascular disease and affect fetal development. The lower molecular-weight (two-ring) PAHs are more soluble, and volatile. The larger molecular-weight PAHs are less soluble in water, and five or more ring PAHs are usually solids.
Exhaust emissions from vehicles produce particulate matter containing PAHs. These can be removed by catalytic converters.
Bioaccumulation and Biomagnification
The process by which persistent pollutants, such as PAHs, are accumulated in organisms which are exposed to the source for a long period of time. Plants can absorb pollutants through their roots and show a far higher concentration than the surrounding environment. When herbivores pass the pollutant up the trophic pyramid, the pollutant can concentrate even more. In this case it is referred to as biomagnification.