Air pollutants are an issue in cities and rural areas, and they're a cross-country, international problem. Smog in the United States' Western cities can be partially attributed to coal-burning in China.
Many industrial processes increase air pollution, such as auto emissions, forest fires, and home heating. Air pollution contributes to acid rain, climate change, and poor human health. The World Health Organization (WHO) estimates that 4.6 million people die each year due to complications associated with air pollution.
