On-line measurement of atmospheric oxygen by an open-path OA-ICOS based sensor with high accuracy at ambient pressure

•We developed an open-path OA-ICOS based sensor system for real-time O2 measurements at ambient pressure without pressure control.•The influence of pressure on the OA-ICOS sensor system was studied theoretically and experimentally.•A pressure measurement method for OA-ICOS based on the self-defined linewidth broadening factor was proposed.•An effective pressure correction method was proposed and verified by experiment.