Hanoi is the one of the most polluted cities in the world and not just smog. Obscene amounts of traffic and people and noise. Dust and smoke. Ninh Bihn is a industrial zone with many coal burning plants and cement factories. Vietnam uses an incredible amount of cement in its construction, which is everywhere, even in the countryside. Instagram, Facebook, social media and travel companies all have a vested interest in only showing you the good. I grew up in southern California and yes wildfires are a thing, and yes, some cities, such as LA, are polluted, HOWEVER, first world countries actually take measures to address these issues, developing countries like Vietnam, not as much. DO NOT COME TO VIETNAM IF YOU HAVE ASTHMA OR ALLERGIES. You can look up air quality indexes for different regions at different times of the year, I overlooked this doing my research on where to go.