Introduction
As the most significant environmental threat to human health, air
pollution exposure may account for as many as 1 in 5 deaths
worldwide.1,2 The burden of disease disproportionately
affects residents of low- and middle-income countries where air quality
continues to worsen in contrast to high-income
countries.1 The World Health Organization (WHO) last
issued health-based guidelines for major air pollutants in 2006:Air quality guidelines – global update 2005. Particulate matter,
ozone, nitrogen dioxide and sulfur dioxide .3 Since
then, methods of assessing air pollution exposure have
improved.1 Studies on the relationship between air
pollution and health have been conducted in nearly all WHO regions,
whereas most prior studies were of North American and European
origin.1 New evidence has linked air pollution with
asthma, diabetes, reproductive outcomes, various neurocognitive
endpoints, and other health conditions with which associations were not
previously suspected.1,4,5 In light of these
developments, the WHO has released a global update to its air quality
guidelines.
The purpose of the guideline is to provide key stakeholders and
decision-makers with 1) evidence-based air quality guideline (AQG)
levels, or the lowest levels of exposure that result in harms to health,
for particulate matter 2.5 (PM2.5), particulate matter
10 (PM10), nitrogen dioxide, ozone, sulfur dioxide, and
carbon monoxide in both indoor and outdoor environments; 2) interim
target levels to guide the reduction of these pollutants in countries
that significantly exceed AQG levels; and 3) good practice statements to
guide mitigation efforts for specific types of PM that pose a health
risk but lack sufficient evidence to derive AQGs.