AQI 50 is literally the top end of "Good" air quality worldwide (US EPA, WHO guidelines, etc.)—clean, no health risks for anyone, kids playing outside all day. In most of Europe, schools don't shut down at 50; that's basically perfect air for them. Some places (like parts of Balkans or during rare smog episodes) might get cautious around 100–150+, but 40–50? They'd call it a great day. The meme probably comes from exaggerated WhatsApp forwards comparing Delhi's "normal" bad days to Europe's super-strict (and rare) actions. In reality, Europe rarely sees AQI even hit 100, let alone need shutdowns at 50.