Seasonal and spatial changes in trace gases over megacities from Aura TES observations - two case studies

Sep 10, 2026

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Aura Tropospheric Emission Spectrometer (TES) measurements provide closely spaced observations over 19 megacities to improve understanding of processes controlling air quality and to characterize seasonal and interannual variability. Two urban regions are analyzed: Mexico City metropolitan area (MCMA) and the area near Lagos (Nigeria). TES observations of ozone, ammonia, methanol, and formic acid show seasonal signals correlated with AIRS CO and MODIS aerosol optical depth, confirmed by in situ data for MCMA and by GEOS-Chem model output for Lagos. TES also identifies an extreme pollution event in MCMA and stronger biomass-burning impacts south of the MCMA caldera, plus enhanced trace gases south of Lagos over the Gulf of Guinea, enabling direct comparison between cities from the same platform and retrieval methods.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages20

Reading Time50 min

AccessFree to download

Abstract

Introduction

Megacities and air-quality challenges

Sources, transport, and climate impacts

Measurement approaches and limitations

Atmos. Chem. Phys., 17, 9379–9398, 2017 [https://doi.org/10.5194/acp-17-9379-2017](https://doi.org/10.5194/acp-17-9379-2017)[ ](https://doi.org/10.5194/acp-17-9379-2017)© Author(s) 2017 . This work is distributed under the Creative Commons Attribution 3 .0 License. Seasonal and spatial changes in trace gases over megacities from Aura TES observations: two case studies Karen E. Cady-Pereira 1 , Vivienne H. Payne2 , Jessica L. Neu2 , Kevin W. Bowman2 , Kazuyuki Miyazaki2,3 , Eloise A. Marais4,a, Susan Kulawik5 , Zitely A. Tzompa-Sosa6 , and Jennifer D. Hegarty 1 1Atmospheric and Environmental Research, Lexington, MA, USA 2Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA 3Japan Agency for Marine-Earth Science and Technology, Yokohoma, Kanagawa Prefecture, Japan 4 School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA 5Bay Area Environmental Research Institute/NASA Ames, Mountain View, CA, USA 6Department of Atmospheric Sciences, Colorado State University, Colorado Springs, CO, USA anow at: School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, UK Correspondence to: Karen E. Cady-Pereira ([kcadyper@aer.com](kcadyper@aer.com)) Received: 3 February 2017 – Discussion started: 6 March 2017 Revised: 3 July 2017 – Accepted: 4 July 2017 – Published: 7 August 2017 Abstract. The Aura Tropospheric Emission Spectrometer (TES) is collecting closely spaced observations over 19 megacities. The objective is to obtain measurements that will lead to better understanding of the processes affecting air quality in and around these cities, and to better estimates of the seasonal and interannual variability. We explore the TES measurements of ozone, ammonia, methanol and formic acid collected around the Mexico City metropolitan area (MCMA) and in the vicinity of Lagos (Nigeria) . The TES data exhibit seasonal signals that are correlated with Atmospheric Infrared Sounder (AIRS) CO and Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical depth (AOD), with in situ measurements in the MCMA and with Goddard Earth Observing System (GEOS)-Chem model output in the Lagos area. TES was able to detect an extreme pollution event in the MCMA on 9 April 2013, which is also evident in the in situ data. TES data also show that biomass burning has a greater impact south of the city than in the caldera where Mexico City is located. TES measured enhanced values of the four species over the Gulf of Guinea south of Lagos. Since it observes many cities from the same platform with the same instrument and applies the same retrieval algorithms, TES data provide a very useful tool for easily comparing air quality measures of two or more cities. We compare the data from the MCMA and Lagos, and show that, while the MCMA has occasional extreme pol- lution events, Lagos consistently has higher levels of these trace gases. 1 Introduction The world's megacities, deﬁned as urban agglomerations with a population over 10 million (UN, 2016), currently house close to 500 million people, about one-eighth of the global urban population (UN, 2014) . They have increased in number, from 2 in 1950 (New York–Newark and Tokyo– Yokohama) to 28 in 2014, and have also become increasingly larger. This growth is expected to continue, as more and more people leave rural areas for better opportunities and a higher quality of life. Yet while it has been shown that urban dwellers are ﬁnancially better off, better educated and better fed, this improvement does come at the cost of strained services and increased congestion, causing, among other problems, increases in urban water and air pollution. The fastestgrowing megacities in the past few decades have been located primarily in the developing world (UN, 2014), where rapid industrialization in combination with high population density and limited emission controls is leading to serious air quality problems (UN, 2

FAQs

What observational platform and instrument are used in the study?

The study uses Aura’s Tropospheric Emission Spectrometer (TES) to collect closely spaced observations over 19 megacities and analyze trace-gas behavior.

Which trace gases and cities are examined in the two case studies?

The analysis focuses on ozone, ammonia, methanol, and formic acid, using the Mexico City metropolitan area (MCMA) and the vicinity of Lagos (Nigeria) as two case-study regions.

How do TES results relate to other satellite data and supporting datasets?

Seasonal TES signals correlate with AIRS CO and MODIS aerosol optical depth; MCMA results are supported by in situ measurements, while Lagos results are supported by GEOS-Chem model output.

Sep 10, 2026

Upload by Mabel