<p>We present an updated (v2) catalog of NO<sub>x</sub> emissions from point sources&#160;<br>as derived from TROPOMI measurements of NO<sub>2</sub> (PAL product) combined with wind fields from ERA5.<br>Several improvements have been introduced to the algorithm.&#160;<br>Most importantly, several corrections are applied,&#160;<br>accounting for the effects of plume height on satellite sensitivity, 3D topographic effects,&#160;<br>and the chemical loss of NO<sub>x</sub>,&#160;<br>resulting in considerably higher and more accurate NO<sub>x</sub> emissions.&#160;<br>In addition, error estimates are provided for each point source.<br>&#160; &#160; &#160; &#160;&#160;<br>The catalog v2 is based on a fully automated iterative detection algorithm of point sources worldwide.<br>It lists 1139 locations that have been found to be significant NO<sub>x</sub> sources.<br>The majority of these locations match to power plants listed in the global power plant database.<br>Other NO<sub>x</sub> point sources correspond to cement plants, metal smelters, industrial areas, or medium-sized cities.<br>&#160; &#160; &#160; &#160;&#160;<br>The emissions listed in v2 of the catalog show good agreement (within 20% on average)&#160;<br>to emissions reported by German Environment Agency (Umweltbundesamt, UBA)&#160;<br>as well as the United States Environmental Protection Agency (EPA).&#160;</p>
Abstract. We investigate effects of the 3-dimensional (3D) structure of volcanic plumes on the retrieval results of satellite and ground based UV-vis observations. For the analysis of such measurements usually 1D scenarios are assumed (the atmospheric properties only depend on altitude). While 1D assumptions are well suited for the analysis of many atmospheric phenomena, they are usually less appropriate for narrow trace gas plumes. For UV/vis satellite instruments with large ground pixel sizes like GOME-2, SCIAMACHY, or OMI, 3D effects are of minor importance, but usually these observations are not sensitive to small volcanic plumes. In contrast, observations of TROPOMI aboard Sentinel-5P have a much smaller ground pixel size (3.5 × 5.5 km2). Thus on the one hand, TROPOMI can detect much smaller plumes than previous instruments. On the other hand 3D effects become more important, because the TROPOMI ground pixel size is smaller than the height of the troposphere and also smaller than horizontal atmospheric photon path lengths in the UV/vis spectral range. In this study we investigate the following 3D-effects using Monte-Carlo radiative transfer simulations: 1. the light mixing effect caused by horizontal photon paths, 2. the saturation effect for strong SO2 absorption, 3. geometric effects related to slant illumination and viewing angles, and 4. Plume side effects related to slant illumination angles and photons reaching the sensor from the sides of volcanic plumes. Especially the first two effects can lead to a strong and systematic underestimation if 1D retrievals are applied (more than 50 % for the light mixing effect, and up to 100 % for the saturation effect). Besides the atmospheric radiative transfer, the saturation effect also affects the the spectral retrievals. Geometric effects have a weaker influence on the quantitative analyses, but can lead to a spatial smearing of elevated plumes or even to virtual double plumes. Plume side effects are small for short wavelengths, but can become large for longer wavelengths (up to 100 % for slant viewing and illumination angles). For ground based observations, most of the above mentioned 3D effects are not important, because of the narrow FOV and the closer distance between the instrument and the volcanic plume. However, the light mixing effect shows a similar strong dependence on the horizontal plume extension as for satellite observations and should be taken into account for the analysis of ground based observations.
Abstract. We present an updated (v2) catalog of NOx emissions from point sources as derived from TROPOspheric Monitoring Instrument (TROPOMI) measurements of NO2 (Products Algorithm Laboratory (PAL) product) combined with wind fields from ERA5. Compared to version 1 of the catalog (Beirle et al., 2021), several improvements have been introduced to the algorithm. Most importantly, several corrections are applied, accounting for the effects of plume height on satellite sensitivity, 3D topographic effects, and the chemical loss of NOx, resulting in considerably higher and more accurate NOx emissions. In addition, error estimates are provided for each point source, taking into account the uncertainties of the individual retrieval steps. The v2 catalog is based on a fully automated iterative detection algorithm of point sources worldwide. It lists 1139 locations that have been found to be significant NOx sources. The majority of these locations match power plants listed in the Global Power Plant Database (GPPD). Other NOx point sources correspond to cement plants, metal smelters, industrial areas, or medium-sized cities. The emissions listed in v2 of the catalog show good agreement (within 20 % on average) to emissions reported by the German Environment Agency (Umweltbundesamt, UBA) as well as the United States Environmental Protection Agency (EPA). The data are publicly available at https://doi.org/10.26050/WDCC/No_xPointEmissionsV2 (Beirle et al., 2023).
Abstract. We investigate effects of the three-dimensional (3D) structure of volcanic plumes on the retrieval results of satellite and ground-based UV–Vis observations. For the analysis of such measurements, 1D scenarios are usually assumed (the atmospheric properties only depend on altitude). While 1D assumptions are well suited for the analysis of many atmospheric phenomena, they are usually less appropriate for narrow trace gas plumes. For UV–Vis satellite instruments with large ground pixel sizes like the Global Ozone Monitoring Experiment-2 (GOME-2), the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) or the Ozone Monitoring Instrument (OMI), 3D effects are of minor importance, but usually these observations are not sensitive to small volcanic plumes. In contrast, observations of the TROPOspheric Monitoring Instrument (TROPOMI) on board Sentinel-5P have a much smaller ground pixel size (3.5 × 5.5 km2). Thus, on the one hand, TROPOMI can detect much smaller plumes than previous instruments. On the other hand, 3D effects become more important, because the TROPOMI ground pixel size is smaller than the height of the troposphere and also smaller than horizontal atmospheric photon path lengths in the UV–Vis spectral range. In this study we investigate the following 3D effects using Monte Carlo radiative transfer simulations: (1) the light-mixing effect caused by horizontal photon paths, (2) the saturation effect for strong SO2 absorption, (3) geometric effects related to slant illumination and viewing angles and (4) plume side-effects related to slant illumination angles and photons reaching the sensor from the sides of volcanic plumes. The first two effects especially can lead to a strong and systematic underestimation of the true trace gas content if 1D retrievals are applied (more than 50 % for the light-mixing effect and up to 100 % for the saturation effect). Besides the atmospheric radiative transfer, the saturation effect also affects the spectral retrievals. Geometric effects have a weaker influence on the quantitative analyses but can lead to a spatial smearing of elevated plumes or even to virtual double plumes. Plume side-effects are small for short wavelengths but can become large for longer wavelengths (up to 100 % for slant viewing and illumination angles). For ground-based observations, most of the above-mentioned 3D effects are not important because of the narrow field of view (FOV) and the closer distance between the instrument and the volcanic plume. However, the light-mixing effect shows a similar strong dependence on the horizontal plume extension as for satellite observations and should be taken into account for the analysis of ground-based observations.
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