JAKARTA — The sight of commuters, their faces hidden behind masks while perched on motorcycle taxis, is common across Asia. The bikes weave through gridlock in cities like Jakarta and Bangkok, getting the passengers to work on time. But the masks, sometimes worn by both driver and passenger, hint that the air they breathe might not be the cleanest. Judging from World Health Organization figures released on Wednesday, covering 4,300 cities across 108 countries, the commuters have the right idea. Of an estimated 7 million deaths worldwide per year from air pollution, just over two-thirds occur in Asia, which is home to slightly less than 60% of the global population. Breaking the numbers down, the 10 countries in the WHO’s “South-east Asia” region account for about a quarter of the world’s population but suffer around 2.4 million, or 34%, of all air pollution deaths.