Determination of the Emission Rates of CO 2 Point Sources with Airborne Lidar

Abstract. Anthropogenic point sources, such as coal-fired power plants, produce a major share of global CO2 emissions. International climate agreements demand their independent monitoring. Due to the high amount of point sources and their global spatial distribution, a mobile measurement approach with fast spatial coverage is needed. Active remote sensing measurements by airborne lidar show much promise in this respect. The integrated-path differential-absorption lidar CHARM–F is installed onboard an aircraft, in order to detect weighted vertical columns of CO2 mixing ratios, below the aircraft along its flight track. During the Carbon Dioxide and Methane mission (CoMet) in spring 2018, airborne greenhouse gas measurements were performed, focusing on the major European sources of anthropogenic CO2 emissions, i.e. large coal–fired power plants. The flights were designed to transect isolated exhaust plumes. From the resulting enhancement in the CO2 mixings ratios, emission rates can be derived in terms of the cross–sectional flux method. On average, we find our results roughly corresponding to reported annual emission rates, but observe significant variations between individual overflights ranging up to a factor of 2. We suppose that these variations are mostly driven by turbulence. This hypothesis is supported by a high–resolution large eddy simulation that enables us to give a qualitative assessment of the influence of plume inhomogeneity on the cross–sectional flux method. Our findings suggest avoiding periods of strong turbulence, e.g. midday and afternoon. More favorable measurement conditions prevail during nighttime and morning. Since lidars are intrinsically independent of sunlight, they have a significant advantage in this regard.