The 2016 London atmospheric emissions inventory estimates that, the construction sector contributes 34% of the total PM10 and 7% of the total NOX – the largest and 5th largest sources, respectively. Recent on-road light duty diesel vehicle emission tests have shown significant differences between real-world NOX emissions compared with results from laboratory based regulatory tests. The aim of this study was therefore to quantify the ‘real-world’ tail-pipe NOX, CO2, and particle emissions, for 30 of the most commonly used construction machines in London under normal working conditions. The highest NOX emissions (g/kWh) were from the older engines (Stage III-A ~4.88 g/kWh and III-B ~4.61 g/kWh), these were reduced significantly (~78%) in the newer (Stage IV ~1.05 g/kWh) engines due to more advanced engine management systems and exhaust after treatment. One Stage IV machine emitted NOX similar to a Stage III-B machine, the failure of this SCR was only detectable using PEMS as no warning was given by the machine. Higher NOX conformity factors were observed for Stage IV machines, due to the lower NOX emission standards, which these machines must adhere to. On average, Stage III-B machines (~525 g/kWh) emitted the lowest levels of CO2 emissions, compared to Stage III-A (~875 g/kWh) and Stage IV (~575 g/kWh) machines. Overall, a statistically significant (~41%) decrease was observed in the CO2 emissions (g/kWh) between Stage III-A and III-B machines, while no statistically significant difference was found between Stage III-B and IV machines. Particle mass measurements, which were only measured from generators, showed that generators of all engine sizes were within their respective Stage III-A emission standards. A 95% reduction in NOX and 2 orders of magnitude reduction in particle number was observed for a SCR-DPF retrofitted generator, compared to the same generator prior to exhaust gas after-treatment strategy. Display omitted •NOX, CO2, and particulate exhaust emissions from a total of 30 construction machines, including 9 different types.•PEMS measurements were carried out on active construction sites in London, giving an indication of ‘real-world’ emissions.•Measured NOX emissions indicate that approximately 75% of the machines tested conform to within a factor of 2.1.