en تست و استاندارد Standards and tests پژوهشي Research <span style="font-size:10pt"><span new="" roman="" style="font-family:" times="">This study develops and validates a simplified testing methodology aligned with UNECE Regulation No. 49 to quantify particle number (PN) emissions from diesel vehicles. A modified World Harmonized Vehicle Cycle (WHVC) was implemented, incorporating steady-state operational segments (urban: 21.3 km/h, rural: 43.6 km/h, motorway: 76.7 km/h), and applied to evaluate 51 Iranian-manufactured diesel vehicles. The tested fleet comprised heavy-duty trucks, buses, and pickup trucks equipped with diverse propulsion systems (e.g., ISF3.8s5154, OM457LA.IV) and after-treatment technologies, including SCR, DOC, and DPF. Results demonstrate that original equipment manufacturer (OEM)-installed DPFs reduced PN emissions by 7000-fold compared to non-DPF-equipped vehicles (2.49 &times; 10&sup1;⁰ vs. 1.74 &times; 10&sup1;⁴ particles/km; p < 0.001). Euro VI-compliant vehicles exhibited the lowest emissions (6.01 &times; 10&sup1;⁰ particles/km), outperforming Euro V and Enhanced Environmentally Friendly Vehicle (EEV) standards. These findings underscore the necessity of adopting OEM-grade filtration systems and enforcing stringent emission regulations, such as Euro VI, to mitigate particulate pollution in urban environments. The methodology provides a replicable framework for emerging markets to align with global emission compliance protocols.</span></span><br> &nbsp; Test cycle, Particle number, Emission standards, Diesel fuel, Air pollution 4654 4666 http://ase.iust.ac.ir/browse.php?a_code=A-10-827-1&slc_lang=en&sid=1 Mahdi Keyhanpour kasra.keyhanpoor@gmail.com 180031947532846004805 180031947532846004805 Yes K. N. T. University of Technlogy Fatemeh Sadat Mirabedini mirabedinyfateme@gmail.com 180031947532846004806 180031947532846004806 No K. N. T. University of Technlogy Majid Ghassemi ghasemi@kntu.ac.ir 180031947532846004807 180031947532846004807 No K. N. T. University of Technlogy