Anthropogenic and volcanic point source SO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; emissions derived from TROPOMI on board Sentinel-5 Precursor: first results

Debora Griffin,Vitali Fioletov,Diego G. Loyola,Pascal Hedelt,Chris A. McLinden,Can Li,Nickolay A. Krotkov,Nicolas Theys

doi:10.5194/acp-20-5591-2020

Abstract

Abstract. The paper introduces the first TROPOMI-based sulfur dioxide (SO2) emissions estimates for point sources. A total of about 500 continuously emitting point sources releasing about 10 kt yr−1 to more than 2000 kt yr−1 of SO2, previously identified from Ozone Monitoring Instrument (OMI) observations, were analyzed using TROPOMI (TROPOspheric Monitoring Instrument) measurements for 1 full year from April 2018 to March 2019. The annual emissions from these sources were estimated and compared to similar estimates from OMI and Ozone Mapping Profiling Suite (OMPS) measurements. Note that emissions from many of these 500 sources have declined significantly since 2005, making their quantification more challenging. We were able to identify 274 sources where annual emissions are significant and can be reliably estimated from TROPOMI. The standard deviations of TROPOMI vertical column density data, about 1 Dobson unit (DU, where 1 DU =2.69×1016 molecules cm−2) over the tropics and 1.5 DU over high latitudes, are larger than those of OMI (0.6–1 DU) and OMPS (0.3–0.4 DU). Due to its very high spatial resolution, TROPOMI produces 12–20 times more observations over a certain area than OMI and 96 times more than OMPS. Despite higher uncertainties of individual TROPOMI observations, TROPOMI data averaged over a large area have roughly 2–3 times lower uncertainties compared to OMI and OMPS data. Similarly, TROPOMI annual emissions can be estimated with uncertainties that are 1.5–2 times lower than the uncertainties of annual emissions estimates from OMI. While there are area biases in TROPOMI data over some regions that have to be removed from emission calculations, the absolute magnitude of these are modest, typically within ±0.25 DU, which can be comparable with SO2 values over large sources.

Highlights

Sulfur dioxide (SO2) is a major air pollutant that contributes to acid rain and aerosol formation, adversely affects the environment and human health, and impacts climate
In the TROPOspheric Monitoring Instrument (TROPOMI) spectral fit, an SO2 cross section at 203 K was used, and the retrieved vertical column densities (VCDs) were adjusted by applying an air mass factors (AMFs) correction factor using temperatures from the European Centre for Medium-Range Weather Forecast (ECMWF) operational model (Theys et al, 2017)
To remove the systematic difference with Ozone Monitoring Instrument (OMI)/Ozone Mapping Profiling Suite (OMPS) data caused by the difference in cross-section temperature (203 K for TROPOMI vs. 293 K for OMI/OMPS), we increased the TROPOMI SO2 VCDs by 22 %

Summary

Introduction

Sulfur dioxide (SO2) is a major air pollutant that contributes to acid rain and aerosol formation, adversely affects the environment and human health, and impacts climate. Liu et al (2018) demonstrated that merging such satellite-based emissions estimates with a conventional bottom-up inventory improves the agreement between the model and surface observations. The operational TROPOMI SO2 retrieval algorithm utilizes the DOAS approach (Theys et al, 2017), and early observations demonstrated the benefits of high spatial resolution for monitoring volcanic plumes (Hedelt et al, 2019; Theys et al, 2019; Queißer et al, 2019). These first studies were focussed on relatively high volcanic SO2 levels. About 500 SO2 sources, previously identified using OMI 2005–2015 data (Fioletov et al, 2016), were examined, and their emissions were estimated using TROPOMI data and compared to emissions estimates from OMI and OMPS

Satellite SO2 vertical column density data

Air mass factors and data filtering

Wind and snow data

TROPOMI SO2

Emissions estimates

Findings

Summary and discussion