In this work, we compare the two most widely used online XRF monitors for ambient elemental analysis, the Xact625i and PX-375. We found strong correlations between the online instruments and the reference method (better so for the Xact625i), while in terms of absolute concentrations, some elements were over- and underestimated. Overall, we determined both instruments can be used as powerful tools to produce high-time resolution elemental data for use in air quality monitoring.