Most power plants, incinerators, and garbage dumps are built near where the poor people live. In Washington, DC, the Capitol power plant has been burning coal which pollutes areas where poor people live and have higher than average rates of asthma. The plant has been able to burn natural gas which pollutes a lot less, but recent efforts may have finally succeeded in forcing them to switch from coal.
BS
Poor people have higher incidence of asthma because they spend so much of their childhood breathing climate controlled air.
Most of the poor (a nonsensical term in modern America) keep their children in doors as much as possible in their urban ghettos. Most of the poor have air conditioning so the windows stay shut.
With modern AC equipped with HEPA filters every bit of pollen, air born bacteria, mold spoor, and dust particle is filter out of the atmosphere they breathe. This ultra clean air means that the children from the earliest age are not exposed to contaminants that they would be if they spent a good part of their time outdoors.
So their immune systems not challenged by normal air contaminants from the earliest age their immune systems become ultra-sensitive to what should be normal exposure to typical air contaminants.