Abstract: In some settings like school classrooms, CO2 measurements have shown to be a very useful method to infer the risk of far-field airborne infection. Often only a single point measurement is available which cannot capture spatial variations, likely to be encountered in naturally ventilated spaces where the room might not be well mixed. As a cost-effective tool, CO2 sensors are in increasingly widespread use and so it is crucial to understand how exposure might differ depending on the source location and/or sensor position. This is investigated using RANS simulations in a typical naturally ventilated UK classroom in wintertime.