Delhi air quality: Judges accuse authorities of ‘passing the buck’

India’s top court has accused state governments of “passing the buck” on air pollution and failing to take action to tackle Delhi’s toxic smog. The Supreme Court said authorities were only interested in “gimmicks”, rather than concrete measures to combat pollution levels. Levels of dangerous particles in the air – known as PM2.5 – are at well over 10 times safe limits in the capital. “Delhi is choking every year and we are unable to do anything,” said Supreme Court Justice Arun Mishra. “The state machinery is not acting… They are passing the buck to each other… Everybody is interested in gimmicks and elections.” From 4 to 15 November, cars with odd or even number plates will only be allowed on the roads on alternate days, officials said. Such a system has been used before but it is not clear if it helps lower pollution levels. Cars are not believed to be the main cause of Delhi’s toxic air, with experts pointing instead to crop burning by farmers in neighbouring states to clear fields. Health officials have asked people to stay indoors and refrain from doing any physical activity as millions are ...

Appliance Science: HEPA filters and the physics of fresh air

HEPA air filters promise to take nasty things out of the air, removing cigarette smoke, pollen and other irritants. How do they do this? Appliance Science looks at how HEPA air filters work, and how to tell the real from the fake. Fresh air? More like stinky, germ-filled and particle-laden air. The air that you breathe is filled with all manner of things, from visible dust to invisible (but stinky) chemicals. Most of these things are harmless, but some can be harmful to your health, especially for those with conditions such as asthma. For these people, relief can come in the form of a HEPA (short for “High Efficiency Particulate Arrestance” or “Air,” depending on who you ask) filter that removes the ick, pumping out clean, stink and dust-free air. HEPA is a US government standard, first set in 1983. The standard says that to earn the name, a filter must capture at least 99.97 percent of particles larger than 0.3 µm (micrometers, or microns) in size, while only impeding the flow of air by a relatively small amount. The progression of modern of air filters design goes back much further, though: the technology behind them was developed to capture tiny radioa...