The app on my phone tells me that the AQI level is two. My lungs tell me the same as I let the fresh, odourless, crisp, rejuvenating air flood my respiratory system. Alas, this is not my city. This is London. At the same moment, my city of New Delhi records an AQI of 342, and even this looks like a good day in terms of air quality, at least when compared to the many 500+ days we have seen this winter.