title: Letter: Sources of urban air pollution.
mesh_terms: D000397:Air Pollution / Q000517:prevention & control; D001336:Automobiles; D005579:Fossil Fuels; D007221:Industry; D014481:United States; D001335:Vehicle Emissions / Q000517:prevention & control
chemical_list: D005579:Fossil Fuels; D001335:Vehicle Emissions