Acid deposition is related to smog and visibility/regional haze through common emissions and precursors, production pathways, and meteorological processes. Emissions of sulphur dioxide (SOx) and nitrogen oxides (NOx) from coal- and oil-fired power plants, smelters, motor vehicles, and other human-related sources are the principal contributors to acid deposition, ground-level ozone, and particulate matter. Fine particulate matter is the main cause of poor visibility and regional haze. Reductions in SO2 and NOx will result in improvements in acid deposition, PM, visibility and ozone.
There are also linkages between acid rain and both ozone layer depletion and climate change. The interactions between acid rain, ultraviolet (UV) radiation and climate change can magnify the impacts of acid rain. For example, because acidity reduces the amount of dissolved organic matter in lake water, acidic lakes are clearer and therefore more vulnerable to the effects of increased UV levels. Climate change can affect acid levels in lakes, because hot, dry conditions convert harmless sulphur compounds that have accumulated in wetlands into acid-forming sulphates. When it rains, these sulphates are flushed into surrounding lakes, boosting their acid levels.
Emissions of mercury and other hazardous pollutants work in synergy with SO2 and NOx to worsen the harmful effects of acid deposition on fish and wildlife. Increasing acidity of water bodies increases the rate of conversion of mercury into toxic and bioavailable methyl mercury (MeHg). Recent studies have shown that significant declines in atmospheric deposition of sulphate and Hg are associated with declines in Hg levels in fish and fish consuming wildlife such as the common loon.
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