Environmental pollution (urban air): Which metal is a major pollutant in the air of large cities? Consider historical vehicular emissions and legacy contamination from fuels and industry. Choose the correct metal.

Given data

• Context: Big-city air quality, traffic-related emissions.

Concept/Approach
For decades, lead was emitted from leaded gasoline (tetraethyl lead). Though phased out in many countries, urban dust/soil often retains legacy lead; industrial sources also contribute.

Reasoning
Leaded petrol → exhaust aerosols with Pb compounds → ambient air/dust contamination.

Common pitfalls
Chromium and cadmium are industrial toxins but less ubiquitous in traffic-related ambient air than historical lead.

Final Answer
Lead