We present a new mobile environmental reaction chamber for the simulation of the atmospheric aging of aerosols from different emissions sources without limitation from the instruments or facilities available at any single site. The chamber can be mounted on a trailer for transport to host facilities or for mobile measurements. Photochemistry is simulated using a set of 40 UV lights (total power 4 KW). Characterisation of the emission spectrum of these lights shows that atmospheric photochemistry can be accurately simulated over a range of temperatures from −7–25 °C. A photolysis rate of NO₂, J_NO2, of (8.0 ± 0.7) × 10⁻³ molecules cm⁻³s⁻¹ was determined at 25 °C. Further, we present the first application of the mobile chamber and demonstrate its utility by quantifying primary organic aerosol (POA) emission and secondary organic aerosol (SOA) production from a Euro 5 light duty gasoline vehicle. Exhaust emissions were sampled during the New European Driving Cycle (NEDC), the standard driving cycle for European regulatory purposes, and injected into the chamber. The relative concentrations of oxides of nitrogen (NO_x) and total hydrocarbon (THC) during the aging of emissions inside the chamber were controlled using an injection system developed as a part of the new mobile chamber set up. Total OA (POA + SOA) emission factors of (370 ± 18) × 10⁻³ g kg⁻¹ fuel, or (14.6 ± 0.8) × 10⁻³ g km⁻¹, after aging, were calculated from concentrations measured inside the smog chamber during two experiments. The average SOA/POA ratio for the two experiments was 15.1, a much larger increase than has previously been seen for diesel vehicles, where smog chamber studies have found SOA/POA ratios of 1.3–1.7. Due to this SOA formation, carbonaceous particulate matter (PM) emissions from a gasoline vehicle may approach those of a diesel vehicle of the same class. Furthermore, with the advent of emission controls requiring the use of diesel particle filters, gasoline vehicle emissions could become a far larger source of ambient PM than diesel vehicles. Therefore this large increase in the PM mass of gasoline vehicle aerosol emissions due to SOA formation has significant implications for our understanding of the contribution of on-road vehicles to ambient aerosols and merits further study.