Increasing concern over rising pollution levels in city limits has resulted in stringent emission regulations for automotive diesel engines. Exhaust emissions from diesel engines are composed of carbon monoxide, carbon dioxide, hydrocarbons, nitrates, soot particles and soluble organic faction. Post treatment, emission control technique including diesel oxidation catalysis system, diesel particulate filtration system and selective catalytic reduction system have been developed to reduce the emission levels from automotive engines to meet the latest emission norms. Selective catalytic reduction system, which is used for control of nitrate emission has to be intensified to bring down the emission levels as per the requirements for EURO VI and Bharat Stage VI emission norms. This paper provides a comprehensive overview on the post treatment exhaust emission control systems. A detailed literature survey has been conducted on the state of art nitrate emission control technologies including the use of alternate solid reactants for ammonia generation and catalysts for deNOx reactions, considering the adverse effects of byproducts released by these systems.