Over the past few decades there has been considerable progress made in understanding the processes leading to formation and evolution of particulate matter (PM) emissions from heavy duty diesel engines (HDDE). This progress has been primarily made under controlled laboratory conditions with the use of constant volume sampling (CVS) systems and to a limited extend through on-road chase studies. West Virginia University (WVU) is attempting to close the present knowledge gap by conducting detailed experiments in a custom designed and constructed environmental wind tunnel. The understanding and knowledge has recently been further extended to new emission reduction technologies, such as the diesel particulate filter (DPF) which has dramatically changed the size distribution and chemical composition of PM. Additionally, the selective catalytic reduction (SCR) technology has shown to further enhance the formation of nucleation mode particles as well as alter their morphology. Even with advances in technology there remains a considerable gap in the current level of understanding of PM formation and evolution, since the combustion generated PM from diesel engines is not discernible from the atmospheric background PM measured beyond 300m from highways. After being emitted from the vehicle exhaust system, the process of dilution in the atmosphere leads to a multitude of PM transformation phenomena, such as volatilization, coagulation, and condensation. The work presented herein has been divided into two parts which are published separately from each another.The first part describes the design and commissioning process of the wind tunnel focusing on both, aerodynamic and structural constraints, which ultimately led to the definition of the main characteristics of the facility. The resulting design is a subsonic, non-recirculating, suction type tunnel, with a 16ft high and 16ft wide test section capable of housing a full-size heavy-duty tractor cab. A 2,200hp suction fan is employed to provide up to 80 mph wind speeds. The 115ft test cell length guarantees for a 2 second residence time for the exhaust plume evolution (at 35 mph) and complies with turbulence intensity (less than 1%) and quality flow requirement as identified for this type of application. In addition, the West Virginia University (WVU) wind tunnel has been equipped with a custom made sampling system able to move in all three dimensions in order to measure spatially resolved plume characteristics.The second part will describe the actual test procedures and the experimental results and will be published in a separate paper.Copyright © 2012 by ASME