Anthropogenic methane (CH4) emissions contribute significantly to the current radiative forcing driving climate change. Localized CH4 sources such as occurring in the fossil fuel industry contribute a substantial share to the anthropogenic emission total. The temporal dynamics of such emissions is largely unresolved and unaccounted for when using atmospheric measurements by satellites, aircraft and ground-based instruments to monitor emission rates and verify reported numbers. Here, we demonstrate the usage of a ground-based imaging spectrometer for quantifying the CH4 emission dynamics of a ventilation facility of a coal mine in the Upper Silesian Coal Basin, Poland. To this end, we deployed the imaging spectrometer at roughly 1 km distance from the facility and collected plume images of CH4 column enhancements during the sunlit hours of four consecutive days in June 2022. Together with wind information from a co-deployed wind-lidar, we inferredCH4 emission rates with roughly 1 min resolution. Daily average emission rates ranged between 1.39±0.19 and 4.44±0.76 tCH4/h, 10-min averages ranged between (min) 0.82 and (max) 5.83 tCH4/h, and puff-like events caused large variability on time scales below 15 min. Thus, to monitor CH4 emissions from such sources, it requires measurement techniques such as the imaging spectrometer evaluated here that can capture emission dynamics on short time scales.

<p>The global warming potential of methane on a 20-year scale is 80 times larger than that of carbon dioxide. Therefore reducing anthropogenic methane emissions can mitigate greenhouse gas-induced atmospheric warming in the short term. Thus, source attribution and budgeting of methane emissions have received particular attention in recent years. Coal mining activities were found to be accountable for approximately one-tenth of anthropogenic methane emissions. Observations of point sources (like coal mine ventilation shafts) by plume imagery from aircraft of satellites are emerging as a powerful and reliable tool for emission estimates. Yet, while these measurements cover large areas in a short time, the instrument revisiting rates do not allow observation of temporal variability of sources.<br />We present the results of a case study on source dynamics of coal mine ventilation shafts conducted in the Upper Silesian Coal Basin (USCB), Poland, in June 2022. We deployed a HySpex SWIR-384 hyperspectral camera at 1 km distance to a coal mine ventilation shaft. The camera repeatedly observed blue-sky scattered sunlight above the shaft in the shortwave infrared spectral range, taking approximately 1 minute per image. We detect methane plumes reliably using an adapted matched filter algorithm in the 2.3 μm absorption band. Co-located wind-lidar measurements allow us to estimate source emissions rates by the integrated mass enhancement (IME) method. Thereby, we produce several hundred emission estimates per day based on plume imagery, with an average uncertainty below 300 kg/h for minutely estimates under favourable measurement conditions. Our case study covers four consecutive days and reveals substantial source dynamics on all observed time scales from minutes to days. A 10-minute running average of the emissions can be a factor of 2 smaller or larger than the daily mean and daily averaged emissions ranged from 1.39 tCH<sub>4</sub>/h to 4.44 tCH<sub>4</sub>/h.</p>

<p><span dir="ltr" role="presentation">Nitrogen oxides (NO</span><sub><span dir="ltr" role="presentation">x</span></sub>  <span dir="ltr" role="presentation">= NO + NO</span><sub><span dir="ltr" role="presentation">2</span></sub><span dir="ltr" role="presentation">) are atmospheric pollutants that are </span><span dir="ltr" role="presentation">detrimental to air quality and human health and play a major role in tropo</span><span dir="ltr" role="presentation">spheric ozone chemistry.</span> <span dir="ltr" role="presentation">Combustion processes produce NO</span><sub><span dir="ltr" role="presentation">x</span></sub><span dir="ltr" role="presentation">; thus, coal-fired </span><span dir="ltr" role="presentation">power plants contribute significantly to the emission total (EEA 2017). Imag</span><span dir="ltr" role="presentation">ing atmospheric NO</span><sub><span dir="ltr" role="presentation">x</span></sub> <span dir="ltr" role="presentation">columns with the Differential Optical Absorption Spec</span><span dir="ltr" role="presentation">troscopy (DOAS) method is a well-established tool for NO</span><span dir="ltr" role="presentation"><sub>x</sub> </span> <span dir="ltr" role="presentation">emission monitoring </span><span dir="ltr" role="presentation">(e.g. Lohberger 2004; Manago 2018). </span></p> <p><span dir="ltr" role="presentation">During field measurements in June 2022, we deployed a ground-based hy</span><span dir="ltr" role="presentation">perspectral camera (HySpex) for the visible to near-infrared (VNIR) spectral </span><span dir="ltr" role="presentation">range at a distance of 6 km from the largest coal-fired power plant in Europe, </span><span dir="ltr" role="presentation">the Bełchatów Power Station in Poland. We present preliminary results of NO</span><sub><span dir="ltr" role="presentation">2  </span></sub><span dir="ltr" role="presentation">emission plume images using sky-scattered sunlight as the light source.</span> <span dir="ltr" role="presentation">Our </span><span dir="ltr" role="presentation">HySpex VNIR-1800 hyperspectral camera records spatially highly resolved im</span><span dir="ltr" role="presentation">ages with 2400 pixels horizontally and 1800 pixels vertically covering a 22</span><span dir="ltr" role="presentation">°</span><span dir="ltr" role="presentation">x16.5</span><span dir="ltr" role="presentation">° </span><span dir="ltr" role="presentation">field of view at a temporal resolution of</span> <span dir="ltr" role="presentation">∼</span><span dir="ltr" role="presentation">1 minute. The camera covers the spec</span><span dir="ltr" role="presentation">tral range between 400 nm and 1000 nm with a spectral resolution of</span> <span dir="ltr" role="presentation">∼</span><span dir="ltr" role="presentation">5 nm and </span><span dir="ltr" role="presentation">sampling intervals of 3.2 nm.</span> <span dir="ltr" role="presentation">We retrieve pixel-wise differential slant column </span><span dir="ltr" role="presentation">densities of NO</span><sub><span dir="ltr" role="presentation">2</span></sub>  <span dir="ltr" role="presentation">using DOAS in the 420 - 550 nm spectral interval. Despite the </span><span dir="ltr" role="presentation">low spectral resolution, NO</span><sub><span dir="ltr" role="presentation">2</span></sub>  <span dir="ltr" role="presentation">absorption structures can be identified and fitted, </span><span dir="ltr" role="presentation">as we demonstrate by lab measurements with pre-calibrated NO</span><sub><span dir="ltr" role="presentation">2</span></sub>  <span dir="ltr" role="presentation">cells.</span></p> <p><span dir="ltr" role="presentation">We examine the performance of the NO</span><sub><span dir="ltr" role="presentation">2</span></sub>  <span dir="ltr" role="presentation">camera and the potential for com</span><span dir="ltr" role="presentation">bining it with a co-deployed carbon dioxide (CO</span><sub><span dir="ltr" role="presentation">2</span></sub><span dir="ltr" role="presentation">) HySpex camera that operates </span><span dir="ltr" role="presentation">in the shortwave-infrared spectral range. Simultaneous observations of NO</span><sub><span dir="ltr" role="presentation">2</span></sub>  <span dir="ltr" role="presentation">and </span><span dir="ltr" role="presentation">CO</span><sub><span dir="ltr" role="presentation">2</span></sub>  <span dir="ltr" role="presentation">might enable insights into plume dynamics, photochemical processing in </span><span dir="ltr" role="presentation">the plume and the emission ratio of the two species.</span></p> <p> </p> <p><em><span dir="ltr" role="presentation">References:</span></em></p> <p><span dir="ltr" role="presentation">European Environment Agency, 2017</span><em><span dir="ltr" role="presentation">. </span></em><span dir="ltr" role="presentation">Releases of pollutants to the environment from Europe’s industrial sector – 2015. url: https://www.eea.europa.eu /publications/releases-of-pollutants-to-the/releases-of-pollutants-from-industrial-sector (visited on 01/04/2023).</span></p> <p><span dir="ltr" role="presentation">Lohberger, Falko et al.,  Aug. 2004</span><em><span dir="ltr" role="presentation">. “</span></em><span dir="ltr" role="presentation">Ground-based imaging differential optical absorption spectroscopy of atmospheric gases”. In: Applied Optics 43.24, p.4711. </span><span dir="ltr" role="presentation">doi: 10.1364/ao.43.004711. url: https://doi.org/10.1364/ao.43.004711.</span></p> <p><span dir="ltr" role="presentation">Manago, Naohiro et al.,  July 2018</span><em><span dir="ltr" role="presentation">.</span></em><span dir="ltr" role="presentation"> “Visualizing spatial distribution of atmospheric nitrogen dioxide by means of hyperspectral imaging”. In: Applied Optics 57.21, p. 5970. doi: 10.1364/ao.57.005970. url: https://doi.org/10.1364/ao.57.005970.</span></p>