What component in vehicles helps to reduce nitrogen oxide emissions?

Selective Catalytic Reduction (SCR) systems are a crucial technology employed in modern vehicles to significantly reduce nitrogen oxide (NOx) emissions. SCR operates by injecting a urea solution, commonly known as diesel exhaust fluid (DEF), into the exhaust stream. When this fluid is heated in the presence of the exhaust gases, it reacts with nitrogen oxides to convert them into harmless nitrogen and water vapor. This process is particularly effective in diesel engines, which typically produce higher levels of NOx emissions.

The other components mentioned have their roles in emissions control but do not specifically target nitrogen oxides in the same manner. The Mass Air Flow sensor is primarily responsible for measuring the amount of air entering the engine to optimize fuel injection and combustion. Exhaust Gas Recirculation (EGR) reduces NOx emissions by recirculating a portion of the exhaust back into the intake manifold, lowering combustion temperatures, which helps reduce NOx formation during combustion. The catalytic converter is essential for converting harmful pollutants in exhaust gases, including carbon monoxide and unburned hydrocarbons, to less harmful substances but does not focus specifically on the reduction of nitrogen oxides like SCR does.