从给定的一组英文文章中，找到其中与“污染”相关的句子并输出。


以下是一组英文文章：
Air pollution is a major environmental risk to health. By reducing air pollution levels, countries can reduce the burden of disease from stroke, heart disease, lung cancer, and both chronic and acute respiratory diseases, including asthma. The lower the levels of air pollution, the better the cardiovascular and respiratory health of the population will be, both long- and short-term. The “WHO Air quality guidelines” provide an assessment of health effects of air pollution and thresholds for health-harmful pollution levels. In 2016, 91% of the world population was living in places where the WHO air quality guidelines levels were not met.
Air pollution is a major environmental risk to health. By reducing air pollution levels, countries can reduce the burden of disease from stroke, heart disease, lung cancer, and both chronic and acute respiratory diseases, including asthma. The lower the levels of air pollution, the better the cardiovascular and respiratory health of the population will be, both long- and short-term.