Air pollution is a significant concern at Isle Royale National Park. Despite its remote location, pollutants from mainland sources in Canada and the United States, including industrial emissions along the Ohio River Valley, affect the Park's air quality. These pollutants can adversely impact various natural and scenic resources within the park, including soils, surface waters, plants, wildlife, and visibility. Nitrogen and sulfur compounds are among the primary pollutants deposited into Isle Royale NP from the atmosphere. These compounds can have detrimental effects on ecosystem processes, leading to changes in soil and water chemistry. Eutrophication, caused by nitrogen deposition, accelerates the growth of certain species, altering community composition. Meanwhile, acidification resulting from nitrogen and sulfur deposition leaches essential nutrients from soils and water bodies, reducing habitat quality. The Park's susceptibility to these impacts is influenced by factors such as thin, undeveloped soils and low buffering capacity. From 2017 to 2019, total nitrogen deposition in Isle Royale NP ranged from 4.0 to 6.5 kg-N per hectare per year, while total sulfur deposition ranged from 1.6 to 2.4 kg-S per hectare per year. These values were based on the Total Deposition (TDep) model. Boreal lakes within the Park, such as Sargent and Richie, are particularly sensitive to nitrogen enrichment, which can rapidly affect algal communities and lake biodiversity.

The presence of persistent pollutants like mercury poses additional challenges to Isle Royale NP. Mercury, emitted from sources such as power plants on the mainland, can accumulate in the Park's ecosystems, leading to harmful effects on wildlife and human health. Mercury concentrations exceeding safe levels for human consumption have been detected in fish sampled from the park, indicating potential risks to visitors.

Epiphytic macrolichen communities, which grow on tree trunks and branches, are highly sensitive to changes in air pollution. Studies have shown that nitrogen and sulfur deposition levels in the park exceed critical loads necessary to prevent declines in lichen community metrics. Additionally, air pollution modeling indicates that even under changing climate conditions, critical loads for lichen communities may be surpassed at relatively low levels of nitrogen and sulfur deposition.

Visibility impairment due to haze and fine particles of air pollution is another issue faced by Isle Royale NP. On very hazy days, visibility can be reduced from 115 miles to below 45 miles, affecting visitors' ability to enjoy the park's scenic vistas. Despite documented improvements in visibility since the early 2000s, ongoing efforts are needed to address human-caused impairment and achieve the Clean Air Act (1990, 1963) goal of clearer skies

See the below figures to observe the differences and Nitrogen and Sulfur from 2001 - 2021!