How does an Exhaust Gas Recirculation (EGR) system reduce Nitrogen Oxide (NOx) emissions in internal combustion engines?

1. By filtering out nitrogen gas from the intake air before combustion.
2. By redirecting a portion of inert exhaust gas back into the intake manifold, lowering the peak combustion temperature inside the cylinder.
3. By injecting urea into the exhaust line to chemically reduce NOx to nitrogen gas.
4. By enriching the air-fuel mixture to prevent lean combustion conditions.