Retrievals of sulfur dioxide (SO2) from space‐based spectrometers are in a relatively early stage of development. Factors such as interference between ozone and SO2 in the retrieval algorithms often lead to errors in the retrieved values. Measurements from the Ozone Monitoring Instrument (OMI), Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY), and Global Ozone Monitoring Experiment‐2 (GOME‐2) satellite sensors, averaged over a period of several years, were used to identify locations with elevated SO2 values and estimate their emission levels. About 30 such locations, detectable by all three sensors and linked to volcanic and anthropogenic sources, were found after applying low and high spatial frequency filtration designed to reduce noise and bias and to enhance weak signals to SO2 data from each instrument. Quantitatively, the mean amount of SO2 in the vicinity of the sources, estimated from the three instruments, is in general agreement. However, its better spatial resolution makes it possible for OMI to detect smaller sources and with additional detail as compared to the other two instruments. Over some regions of China, SCIAMACHY and GOME‐2 data show mean SO2 values that are almost 1.5 times higher than those from OMI, but the suggested spatial filtration technique largely reconciles these differences.

[1] The eruption of the Eyjafjallajökull volcano, Iceland, in April and May 2010 caused unprecedented disruptions of European air traffic showing that timely monitoring of volcanic ash and SO 2 dispersion as well as the corresponding plume heights are important for aviation safety. This paper describes the observations of SO 2 and BrO columns in the eruption plume and the determination of the SO 2 plume height using the GOME-2 satellite instrument. During the eruptive period in May 2010, SO 2 total columns of up to $20 DU and BrO columns of $7.7 Â 10 13 molec/cm 2 were detected. The BrO/SO 2 ratio estimated from the GOME-2 observations of the Eyjafjallajökull eruption varies from 1.1 Â 10 À4 to 2.1 Â 10 À4. The SO 2 plume heights estimated from the GOME-2 observations on 5 May range from 8-13 km and mostly agree within 1-3 km with visual observations, radar data and modeling results. Furthermore, the GOME-2 SO 2 observations are compared with in situ measurements of the DLR Falcon aircraft on 17 and 18 May 2010 and with Brewer instruments at Valentia, Ireland and Hohenpeissenberg, Germany. The SO 2 columns derived from the Falcon profile measurements range from 0.6-4.7 DU and the comparison with the GOME-2 measurements shows a good agreement, mainly within 1 DU. The Brewer observations at Hohenpeissenberg also agree well with the GOME-2 measurements with a daily average SO 2 column of $1.3 DU during the overpass of the SO 2 cloud on 18 May, whereas the Brewer instrument at Valentia shows up to 50% higher SO 2 columns ($8 DU) on 11 May.Citation: Rix, M., P. Valks, N. Hao, D. Loyola, H. Schlager, H. Huntrieser, J. Flemming, U. Koehler, U. Schumann, and A. Inness (2012), Volcanic SO 2 , BrO and plume height estimations using GOME-2 satellite measurements during the eruption of

The Global Ozone Monitoring Instrument (GOME‐2) was launched on EUMESAT's MetOp‐A satellite in October 2006. This paper is concerned with the retrieval algorithm GOME Data Processor (GDP) version 4.4 used by the EUMETSAT Satellite Application Facility on Ozone and Atmospheric Chemistry Monitoring (O3M‐SAF) for the operational generation of GOME‐2 total ozone products. GDP 4.4 is the latest version of the GDP 4.0 algorithm, which is employed for the generation of official Level 2 total ozone and other trace gas products from GOME and SCIAMACHY. Here we focus on enhancements introduced in GDP 4.4: improved cloud retrieval algorithms including detection of Sun glint effects, a correction for intracloud ozone, better treatment of snow and ice conditions, accurate radiative transfer modeling for large viewing angles, and elimination of scan angle dependencies inherited from Level 1 radiances. Furthermore, the first global validation results for 3 years (2007–2009) of GOME‐2/MetOp‐A total ozone measurements using Brewer and Dobson measurements as references are presented. The GOME‐2/MetOp‐A total ozone data obtained with GDP 4.4 slightly underestimates ground‐based ozone by about 0.5% to 1% over the middle latitudes of the Northern Hemisphere and slightly overestimates by around 0.5% over the middle latitudes in the Southern Hemisphere. Over high latitudes in the Northern Hemisphere, GOME‐2 total ozone has almost no offset relative to Dobson readings, while over high latitudes in the Southern Hemisphere GOME‐2 exhibits a small negative bias below 1%. For tropical latitudes, GOME‐2 measures on average lower ozone by 0% to 2% compared to Dobson measurements.

Abstract. On board the Copernicus Sentinel-5 Precursor (S5P) platform, the TROPOspheric Monitoring Instrument (TROPOMI) is a double-channel, nadir-viewing grating spectrometer measuring solar back-scattered earthshine radiances in the ultraviolet, visible, near-infrared, and shortwave infrared with global daily coverage. In the ultraviolet range, its spectral resolution and radiometric performance are equivalent to those of its predecessor OMI, but its horizontal resolution at true nadir is improved by an order of magnitude. This paper introduces the formaldehyde (HCHO) tropospheric vertical column retrieval algorithm implemented in the S5P operational processor and comprehensively describes its various retrieval steps. Furthermore, algorithmic improvements developed in the framework of the EU FP7-project QA4ECV are described for future updates of the processor. Detailed error estimates are discussed in the light of Copernicus user requirements and needs for validation are highlighted. Finally, verification results based on the application of the algorithm to OMI measurements are presented, demonstrating the performances expected for TROPOMI.

Over the last four decades, space-based nadir observations of sulfur dioxide (SO 2 ) proved to be a key data source for assessing the environmental impacts of volcanic emissions, for monitoring volcanic activity and early signs of eruptions, and ultimately mitigating related hazards on local populations and aviation. Despite its importance, a detailed picture of global SO 2 daily degassing is difficult to produce, notably for lower-tropospheric plumes, due largely to the limited spatial resolution and coverage or lack of sensitivity and selectivity to SO 2 of current (and previous) nadir sensors. We report here the first volcanic SO 2 measurements from the hyperspectral TROPOspheric Monitoring Instrument (TROPOMI) launched in October 2017 onboard the ESA’s Sentinel-5 Precursor platform. Using the operational processing algorithm, we explore the benefit of improved spatial resolution to the monitoring of global volcanic degassing. We find that TROPOMI surpasses any space nadir sensor in its ability to detect weak degassing signals and captures day-to-day changes in SO 2 emissions. The detection limit of TROPOMI to SO 2 emissions is a factor of 4 better than the heritage Aura/Ozone Monitoring Instrument (OMI). Here we show that TROPOMI SO 2 daily observations carry a wealth of information on volcanic activity. Provided with adequate wind speed data, temporally resolved SO 2 fluxes can be obtained at hourly time steps or shorter. We anticipate that TROPOMI SO 2 data will help to monitor global volcanic daily degassing and better understand volcanic processes and impacts.