Why is air pollution from sulphur and nitrogen oxides an issue?

Excess depositions of sulphur and nitrogen oxides are connected to phenomena such as acidification, eutrophication and ground level ozone.

Acidification is the convertion of ammonia (NH3), sulphur dioxide (SO2) and nitrogen oxides (NOx) into acidic substances, which return to the ground in the form of ‘acid rain’. Acid rain is notorious for the damage it causes to forests, lakes, fresh water, coastal ecosystems, soils and monuments. They also assist heavy metals to be released into ground water reservoirs. Acidification is a major environmental problem in Europe. It is a cross-border issue and requires co-ordinated activities across countries and sectors.

Eutrophication refers to the increase of organic matter in the ecosystem, commonly related to the nutrient enrichment at the primary level. At sea, overloads of nitrogen and phosphorous cause excessive growth of plankton algae, alterations in the species composition, malfunctions in the pelagic food web, oxigen depletion, foam formation and death of benthic fauna. Eutrophication does not only affect the structure and functioning of the aquatic ecosystem, it also decreases biodiversity and reduces natural resources of fish and shellfish, affecting maricultures and tourism incomes.

Ground level ozone (O3) is formed by a chemical reaction between nitrogen oxides (NOx) and volatile organic compounds (VOC) in the presence of sunlight. Ozone is a natural constituent of the air we breathe, however at critical concentrations, it becomes harmful (smog). Ozone concentrations can reach unhealthy levels in hot and sunny weather with little wind causing adverse effects on lung function. Ozone concentrations are among the National Ambient Air Quality Standards of United States EPA that lead to NOx trading as a means to control ozone concentration during the summer season.