A visitor vehicle emissions study was conducted for Joshua Tree National Park. This study was a joint effort between the NPS, the National Park Foundation (NPF), and the Volpe National Transportation Systems Center's Environmental Measurement and Modeling Division (Volpe Center). The goal of this study was two-fold: (1) Develop a park-specific baseline vehicular emissions inventory of carbon monoxide (CO), the volatile organic compound (VOC) category of hydrocarbons (HC), nitrogen oxides (NOx), carbon dioxide (CO2), 2.5-micron particulate matter (PM2.5), and 10-micron particulate matter (PM10) NOTE: PM in this document indicates total particulate matter, including exhaust PM (lead, gasoline PM, elemental carbon, organic carbon, and sulfates), brake PM, and tire PM]; and (2) develop a simplified methodology to produce vehicular emissions inventories for varying visitor traffic scenarios.