BrO, SO2 and HCHO

This study is conducted to assess the spatiotemporal variability, trends and anomalies of Ozone Monitoring Instrument (OMI) derived tropospheric formaldehyde (tropo-HCHO) over South Asia land mass and some selected study zones during 2005-2015. This study also discusses anthropogenic emissions of HCHO estimated by MACCity (Monitoring Atmospheric Composition and Climate, MACC and megaCITY – Zoomfor the Environment, CityZEN. Anthropogenic emissions of HCHO have been observed to be averaged at 4.45×10^-13 kg m^-2 s^-1 with an overall increment of 16.5%. The highest sectoral contribution is  seen from transport sector averaged at 5.63×10^-14 kg m^-2 s^-1. OMI data show tropo-HCHO averaged at 6.16±0.24×10¹⁵ molecules cm^-2 with rise of 10.9%. The forest areas of study zone-5 consisting of eastern regions of India, Bangladesh and western regions of Myanmar, appear very prominent source of tropo-HCHO. The dependence of tropo-HCHO column on selected trace gases concentrations and meteorological factors has also been modeled showing reasonable correlation coefficients, up to r=0.94 over peninsular Indian region.

Spaceborne formaldehyde (HCHO) column data have been used in a number of inverse studies as top-down constraints on non-methane hydrocarbon emissions released into the atmosphere from the vegetation, fires and anthropogenic activities (Palmer et  al. 2003, Stavrakou et al. 2009, Barkley et al. 2013, Zhu et al. 2014, Bauwens et al. 2016, Stavrakou et al. 2016). These estimations rely on the formation of HCHO at high yields in the photo-oxidation of the most atmospheric hydrocarbons. This work aims to validate the long-term dataset of formaldehyde (HCHO) column retrievals obtained from the OMI spectrometer in the framework of the EU QA4ECV project (De Smedt et al. 2018). This dataset constitutes a major improvement with respect to previous work thanks to the use of a larger fitting window (328.5-359 nm) allowing for noise reduction, and to a new background correction leading to improved column seasonality. The IMAGES CTM will be used as physical interpolator to assess the quality of the OMI columns. The consistency between OMI and a wide range of measurements will be assessed by using the models to bring together all measurement types (spaceborne, airborne, ground-based) into a unique framework.

The first validation dataset consists in long-term column data retrieved from ground-based FTIR and MAX-DOAS column measurements from 24 stations across the globe, representing different photochemical regimes, ranging from urban and rural regions to high altitude and pristine regions. The ground-based columns are compared to model columns accounting for the location, altitude, a priori profiles and averaging kernels, as well as for the temporal sampling of the measurements. The second validation dataset is an extensive compilation of data merges obtained from past airborne missions (INTEX-B, ARCTAS, DISCOVER-AQ, SENEX, SEAC⁴RS, KORUS-AQ) over North America, Korea, and the Pacific Ocean. Vertical profiles are built from daytime measurements, and the resulting partial columns are used to evaluate the model and the OMI data at the profile locations.

We find that the OMI retrieval shows a large degree of consistency with both validation datasets. The comparisons with aircraft data show a very good agreement for the majority of the missions, except over the Southeast US where the OMI data are found to be biased low by 25% and over the Western US where OMI is biased high by 35%. With respect to ground-based measurements, the OMI biases are within 35% at most sites, but the satellite retrieval is found to be strongly positively biased when compared to Arctic sites (e.g. Eureka, Thule). These discrepancies are further investigated and discussed.

South America is home to the largest rainforest in the world and its significant role on the global climate is widely recognized. This region alone holds about one third of the isoprene emission into the atmosphere, and is prone to intense fire events during the dry season, especially in years of major droughts like 2005 and 2010. Nevertheless, atmospheric composition and related processes in South America remain relatively unexplored, partly due to the inaccessibility of the Amazon forest resulting in the current scarcity of ground-based measurements, and to the South Atlantic anomaly in the Earth’s magnetic field reducing the number and quality of satellite observations.

This study is motivated by the currently incomplete knowledge of the emissions of volatile organic compounds and their monitoring over South America. It takes advantage of the latest formaldehyde (HCHO) column retrievals obtained from the OMI spectrometer in the framework of the EU QA4ECV project, and relies on the fact that the photo-oxidation of the large majority of hydrocarbons released in the atmosphere by vegetation and biomass burning lead to the formation of HCHO at high yields. Satellite observations of HCHO can therefore inform us on the magnitude and spatiotemporal variability of the biogenic and pyrogenic organic compounds.

Here we use the MAGRITTE regional chemistry-transport model and its adjoint to study the atmospheric composition and its seasonal and interannual evolution, by constraining the emissions of isoprene and biomass burning over 2005-2016 in a domain delimited as 15 N-35 S, 32-85 W. MAGRITTE runs at 0.5x0.5 degree horizontal resolution and uses boundary conditions from IMAGESv2 global model simulations (Bauwens et al. 2016, Stavrakou et al. 2018). The regional and global models share the same chemical mechanism, emissions and physical parameterizations. Anthropogenic VOC emissions and their speciation are obtained from EDGARv4.3.2 database (Huang et al. 2017), and from the HTAPv2.2 2010 inventory (Janssens-Maenhout et al. 2015) for the other species. Wildfires are taken from the GFED4 database (van der Werf et al. 2017) and biogenic emissions from the MEGAN-MOHYCAN model (Guenther et al. 2012, Bauwens et al. 2018). Monthly HCHO observations are used as top-down constraints and averaging kernels are taken into account in the calculation of model columns. Individual inversions are conducted for every year.

The optimized ‘top-down’ flux estimates will be analyzed to investigate (i) the seasonality and interannual variability of biogenic emissions over the Amazon basin, (ii) the intensity of biomass burning fluxes during fire events, in particular during major droughts, (iii) potential trends in the biogenic source. The inferred fluxes will be evaluated through model comparisons with ground-based remote sensing data, aircraft data (GABRIEL), and in situ surface concentration measurements.

The Sentinel-5 Precursor (S5P) platform was launched from Northern Russia on October 13, 2017 carrying the TROPOspheric Monitoring Instrument (TROPOMI). With a spatial resolution of 7x3.5 km², TROPOMI provides improved information on natural and anthropogenic emissions of trace gases and aerosols, with an unprecedented level of details. 

BIRA-IASB and DLR have the joint responsibility of developing and maintaining the SO₂ retrieval algorithm and its implementation into the S5P operational processor (Theys et al., 2017).

In this paper, we introduce the algorithm, present the first year of TROPOMI SO₂ results for several degassing volcanoes and anthropogenic sources. Compared to the current OMI, OMPS and GOME-2 sensors, we observe a step change in satellite ability to monitor and quantify global SO₂ point emissions sources. The improvements and new opportunities offered by TROPOMI are illustrated and discussed, and first validation results of the TROPOMI SO₂ product with available concurrent satellite and ground-based measurements are presented. The retrieval challenges associated with higher resolution measurements are also addressed and plans for future work are outlined.

N. Theys, I. De Smedt, H. Yu, T. Danckaert, J. van Gent,C. Hörmann, T. Wagner, P. Hedelt, H. Bauer, F. Romahn, M. Pedergnana, D. Loyola, M. Van Roozendael _: Sulfur dioxide operational retrievals from TROPOMI onboard Sentinel-5 Precursor: Algorithm Theoretical Basis, Atmos. Meas. Tech., 10, 119-153, doi:10.5194/amt-10-119-2017, 2017.

The Sentinel-5 Precursor (S5P) was successfully launched on the 13^th of October 2017, with on board the TROPOspheric Monitoring Instrument (TROPOMI). With a spatial resolution about 15 times finer than OMI, TROPOMI has started to provide important information on natural and anthropogenic emissions of trace gases and aerosols, with an unprecedented level of details. 

The prototype of the TROPOMI tropospheric formaldehyde (HCHO) retrieval algorithm has been developed at BIRA-IASB and implemented at the German Aerospace Center (DLR) in the S5P operational processor UPAS-2 (De Smedt et al., 2018).

In this work, we present the first year of HCHO observations with TROPOMI, with a special focus on the heat wave of summer 2018 over Northern latitudes. We first compare the TROPOMI HCHO observations with the 14-years QA4ECV OMI dataset (http://doi.org/10.18758/71021031) and assess their mutual consistency.  Second, we address the impact of the heat weave that occurred in Northern latitudes last summer (and associated droughts, wildfires and extreme temperatures) on NMVOC emissions during that period. How do the biogenic emissions – traced by HCHO columns - compare to previous Northern latitude summers? What are the TROPOMI capabilities for watching wildfire plumes that occurred e.g. in California, Colorado, Siberia, or in Scandinavian and Iberian Peninsulas? What is the cause of enhanced HCHO levels over (semi)-enclosed water bodies?

De Smedt, I., Theys, N., Yu, H., Danckaert, T., Lerot, C., Compernolle, S., Van Roozendael, M., Richter, A., Hilboll, A., Peters, E., Pedergnana, M., Loyola, D., Beirle, S., Wagner, T., Eskes, H., van Geffen, J., Boersma, K. F., and Veefkind, P.: Algorithm theoretical baseline for formaldehyde retrievals from S5P TROPOMI and from the QA4ECV project, Atmos. Meas. Tech., 11, 2395-2426, https://doi.org/10.5194/amt-11-2395-2018, 2018

In this presentation, the potential of the recently launched TROPOspheric Monitoring Instrument (TROPOMI) I to detect bromine monoxide (BrO) in volcanic plumes is investigated. So far BrO in volcanic plumes has been successfully retrieved from satellite only during major eruptions. The high spatial resolution of S5P/TROPOMI (3.5x7km) and the daily global coverage allow for an investigation of volcanic BrO during small eruptions and even during continuous passive degassing. The continuous observation of passive degassing volcanoes yields the potential for long-term monitoring of volcanoes from satellite. Also, it is expected that the volcanic plumes can be tracked over larger distances.

BrO is a halogen radical altering – inter alia – the atmospheric ozone chemistry. BrO and in particular the molar BrO/SO2 ratios in volcanic gas emissions have been suggested as proxy for monitoring volcanic activity on several accounts.

In this study, we present BrO column densities as well as SO2 column densities retrieved using Differential Optical Absorption Spectroscopy (DOAS) and BrO/SO2 molar ratios in volcanic plumes with varying emission strength from TROPOMI data. By deriving a time series, we investigate the variation of the BrO/SO2 molar ratio of various volcanoes, in order to gain deeper insights into the plume chemistry and emission composition.