Of the following metals, which one pollutes the air of a busy city?

Lead pollution from vehicle exhaust (leaded gasoline) and industrial emissions was a major air pollutant in busy cities before environmental regulations phased it out. While cadmium, chromium, and copper can be toxic pollutants, lead was historically the most significant metal pollutant in urban air due to its widespread use in fuel. Lead poisoning was a serious public health concern in cities.