I must admit that I have given in to buying an air cleaner for my apartment in Beijing. In general, the air is improving here, with weeks at a time having clear skies. On these days I go for a run outside, and use some outdoor exercise equipment. But the air can also become quite thick, although the particles you can’t see are the ones that can do the most damage. Hence the air cleaner.
It is basically a strong fan with a good filter. It helpfully indicates when the air is clean, with a friendly blue light illuminating to tell you it is so. However, when the air is less beneficial, it displays an array of red lights: two means mildly polluted, four more so, and six … However, at some points the machine has a habit of suddenly switching from the blue light to six red lights, with no apparent reason.
After a number of such occurences, I began to suspect that the light system was merely a gimick, to make one feel as though it was doing it’s job. However, then I hit upon the reason: whenever I break wind in its vicinity, it let’s me know it’s displeasure and sets about cleaning up the burst of air pollution.