Updated

Even for a city considered one of the world's dirtiest, the Indian capital hit a new low this week.

Air so dirty you can taste and smell it; a gray haze that makes a gentle stroll a serious health hazard.

According to one advocacy group, government data shows that the smog that enveloped the city midweek was the worst in the last 17 years. The concentration of PM2.5, tiny particulate pollution that can clog lungs, averaged close to 700 micrograms per cubic meter. That's 12 times the government norm and a whopping 70 times the WHO standards.

Yet many of the problems that make Delhi's air toxic continue. People set off massive amounts of festival fireworks, piles of garbage burn, and farmers in bordering regions continue to burn crop waste.