a method or device for reducing harmful emissions from internal-combustion engines before they are released into the atmosphere, for example a filter or a catalytic converter
This particular filter, introduced in 2007, will be the only aftertreatment requiredfor heavy-duty engines in 2010.
b.
(as modifier)
an aftertreatment system
2. medicine
additional treatment that is given to a patient following an illness or medical procedure
3. textiles
a chemical treatment that is applied to a fabric immediately after it has been dyed, in order to make it more colour-fast