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Why can air pollution travel across national borders?

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Wispy cirrus clouds stretch across a bright blue sky above trees and a river at Pinawa Dam Provincial Park in Manitoba, Canada, with sunlight illuminating the scene. — Atmosphere The atmospheres of planets in the solar system are composed of various gases, particulates, and liquids. They are also dynamic places that redistribute heat and other forms of energy. On Earth, the atmosphere provides critical ingredients for living things. Here, feathery cirrus clouds drift across the deep blue sky over Pinawa Dam Provincial Park, near Pinawa, Manitoba, Canada.

Air pollution travels across national borders primarily because many pollutants persist in the atmosphere and are transported over long distances by winds and atmospheric circulation. Because the atmosphere is a continuous gaseous envelope, it does not respect political boundaries, allowing emissions from one region to affect the environment and health of another.1

A primary example of this phenomenon is acid rain. When sulfur dioxide and nitrogen oxides from burning fossil fuels are released, they can be carried across continents before falling as acidic precipitation. For instance, industrial emissions in Great Britain and continental Europe have historically contributed to acid rain in [Norway]. Similarly, chlorofluorocarbons (CFCs) released globally can be transported to the stratosphere over Antarctica, where they contribute to ozone depletion.1

Addressing these issues requires international cooperation, as seen in agreements like the Montreal Protocol, which are essential for mitigating the global impacts of pollution.1