Houston suffers from severe air pollution.
Its notorious lack of zoning (the same that allows for a distinct lack of flood defences) allows industrial facilities to build near residential neighbourhoods, leaving many Houstonians vulnerable to dangerous air pollution. This has led to a persistent increase of atmospheric carbon dioxide, called a “CO2 urban dome”, that is detectable by satellites- Houston is the only metropolitan area with less than ten million citizens where this is possible.
Take the necessary precautions if you suffer from respiratory issues.