A Review on Filtration Techniques for Reduction of Tailpipe Emissions

Tailpipe emissions from internal combustion engines remain a major contributor to urban air pollution, releasing particulate matter (PM), nitrogen oxides (NOx), carbon monoxide (CO), and unburned hydrocarbons (HC). With emission standards such as Bharat Stage VI (BS-VI) and Euro 6 growing stricter, after treatment and filtration technologies have become essential for regulatory compliance. This paper reviews the main techniques for reducing tailpipe emissions, including diesel and gasoline particulate filters (DPF and GPF), three-way catalysts (TWC), selective catalytic reduction (SCR), diesel oxidation catalysts (DOC), and lean NOx traps (LNT). It also examines emerging approaches such as electrostatic precipitation, nano-fiber membrane filters, and zeolite-based adsorbents. Each technique is compared in terms of working principle, filter materials, pollutant removal efficiency, regeneration requirements, backpressure and fuel-economy effects, and cost. The review also considers how these systems perform under real-world driving conditions. The findings show that no single technology addresses all pollutants, and that integrated after treatment systems offer the most effective route to meeting current and future emission norms.