Almost all inhabitants of large cities in low- and middle-income countries face excessively high air pollution, a growing problem that is “wreaking havoc on human health” and causes more than 3 million premature deaths each year, the World Health Organization (WHO) said Thursday.

The agency, hoping to raise awareness and highlight national efforts, said its database now shows more than four in five urban dwellers worldwide live in cities that don’t meet WHO air quality guidelines — 98 percent in poorer countries and 56 percent even in high-income countries.

The findings are part of WHO’s third Global Urban Ambient Air Pollution Database, which examines outdoor air in 3,000 cities, towns and villages — but mostly cities — across 103 countries. It is based on country reports and other sources.