How does the combustion of alkanes (petrol) cause pollution?

(N/A) Octane $(C_8H_{18})$ is a major component of petrol. The combustion of petrol in vehicle engines can be complete or incomplete depending on the availability of oxygen.
$1$. Incomplete combustion occurs when there is a limited supply of oxygen,leading to the formation of carbon monoxide $(CO)$:
$C_8H_{18} + \frac{17}{2} O_2 \xrightarrow{\text{Incomplete combustion}} 8CO + 9H_2O$
$2$. Complete combustion occurs when there is an excess of oxygen,leading to the formation of carbon dioxide $(CO_2)$:
$C_8H_{18} + \frac{25}{2} O_2 \xrightarrow{\text{Complete combustion}} 8CO_2 + 9H_2O$
Carbon monoxide $(CO)$ is a highly poisonous gas that binds with hemoglobin in the blood,reducing its oxygen-carrying capacity. Carbon dioxide $(CO_2)$ is a greenhouse gas that contributes to global warming. Thus,both processes contribute to environmental pollution.