Historically, toxic emissions of Tetraethyl lead ($\text{TEL}$) were primarily associated with:

Tetraethyl lead (${\text{CH}}_3{\text{CH}}_2{)}_4\text{Pb}$ was widely used as an anti-knock additive in gasoline/petrol. Its combustion resulted in significant toxic airborne lead pollution discharged through the exhaust emissions of automobiles before being phased out globally.