摘要：After the accumulation of evidence over 16 years since the last global update in 2005, WHO has released updated global air quality guidelines. 1 The new reference values are considerably lower for most air pollutants than in the previous guidelines. For example, annual means were decreased from 10 to 5 µg/m³ for PM 2·5 , 20 to 15 µg/m³ for PM 10 , and 40 to 10 µg/m³ for nitrogen dioxide. 24-h limits were also lowered, although to a lesser degree. These new reference values reflect findings from studies which have shown that even lower levels of air pollution might be harmful to human health. 2–4 With an estimated global toll of 7 million deaths related to air pollution annually with the previous guidelines in place, it is expected that millions of lives will be saved if countries comply with these new guidelines. Although many countries have their own air quality standards, WHO air quality guidelines are generally stricter, especially if compared with those adopted by low-income and middle-income countries (LMICs). Air quality guidelines, associated with air quality monitoring, have managed to induce a decrease in air pollution levels in many cities and countries over the past two decades. Despite still having high air pollution levels, China, for example, has been managing to substantially reduce its air pollutant levels in the past decade, resulting in health benefits to its population.
