Submicron aerosol pollution in Greater Cairo (Egypt): A new type of urban haze?

Aliki Christodoulou; Spyros Bezantakos; Efstratios Bourtsoukidis; Iasonas Stavroulas; Michael Pikridas; Konstantina Oikonomou; Minas Iakovides; Salwa K Hassan; Mohamed Boraiy; Mostafa El-Nazer; Ali Wheida; Magdy Abdelwahab; Roland Sarda-Estève; Martin Rigler; Giorgos Biskos; Charbel Afif; Agnes Borbon; Mihalis Vrekoussis; Nikos Mihalopoulos; Stéphane Sauvage; Jean Sciare

doi:10.1016/j.envint.2024.108610

Submicron aerosol pollution in Greater Cairo (Egypt): A new type of urban haze?

Environ Int. 2024 Apr:186:108610. doi: 10.1016/j.envint.2024.108610. Epub 2024 Mar 27.

Authors

Aliki Christodoulou¹, Spyros Bezantakos², Efstratios Bourtsoukidis², Iasonas Stavroulas³, Michael Pikridas², Konstantina Oikonomou², Minas Iakovides², Salwa K Hassan⁴, Mohamed Boraiy⁵, Mostafa El-Nazer⁶, Ali Wheida⁶, Magdy Abdelwahab⁷, Roland Sarda-Estève⁸, Martin Rigler⁹, Giorgos Biskos², Charbel Afif¹⁰, Agnes Borbon¹¹, Mihalis Vrekoussis¹², Nikos Mihalopoulos³, Stéphane Sauvage¹³, Jean Sciare²

Affiliations

¹ Climate and Atmosphere Research Center (CARE-C), the Cyprus Institute, Nicosia, 2121, Cyprus; IMT Nord Europe, Institut Mines-Télécom, Univ. Lille, Centre for Energy and Environment, 59000 Lille, France. Electronic address: a.christodoulou@cyi.ac.cy.
² Climate and Atmosphere Research Center (CARE-C), the Cyprus Institute, Nicosia, 2121, Cyprus.
³ Climate and Atmosphere Research Center (CARE-C), the Cyprus Institute, Nicosia, 2121, Cyprus; Institute for Environmental Research and Sustainable Development, National Observatory of Athens, Athens, Greece.
⁴ Air Pollution Research Department, Environment and Climate Change Research Institute, National, Research Centre, El Behooth Str., Giza 12622 Dokki, Egypt.
⁵ Physics and Mathematical Engineering Department, Faculty of Engineering, Port Said University, Port Said, Egypt.
⁶ Theoretical Physics Department, Physics Institute, National Research Centre, El Behooth Str., Giza 12622 Dokki, Egypt.
⁷ Astronomy and Meteorology Department, Faculty of Science, Cairo University, Cairo, Egypt.
⁸ Laboratoire Des Sciences Du Climat Et de l'Environnement (LSCE), CNRS-CEA-UVSQ, Gif-sur-Yvette, France.
⁹ Research and Development Department, Aerosol D.o.o., Ljubjana, Slovenia.
¹⁰ Climate and Atmosphere Research Center (CARE-C), the Cyprus Institute, Nicosia, 2121, Cyprus; Emissions, Measurements, and Modeling of the Atmosphere (EMMA) Laboratory, CAR, Faculty of Science, Saint Joseph University, Beirut, Lebanon.
¹¹ Laboratoire de Météorologie Physique, UMR6016, Université Clermont Auvergne, OPGC, CNRS, 63000 Clermont-Ferrand, France.
¹² Climate and Atmosphere Research Center (CARE-C), the Cyprus Institute, Nicosia, 2121, Cyprus; University of Bremen, Institute of Environmental Physics and Remote Sensing (IUP), Germany; Center of Marine Environmental Sciences (MARUM), University of Bremen, Germany.
¹³ IMT Nord Europe, Institut Mines-Télécom, Univ. Lille, Centre for Energy and Environment, 59000 Lille, France.

PMID: 38626495
DOI: 10.1016/j.envint.2024.108610

Abstract

Greater Cairo, the largest megacity of the Middle East North Africa (MENA) region, is currently suffering from major aerosol pollution, posing a significant threat to public health. However, the main sources of pollution remain insufficiently characterized due to limited atmospheric observations. To bridge this knowledge gap, we conducted a continuous 2-month field study during the winter of 2019-2020 at an urban background site, documenting for the first time the chemical and physical properties of submicron (PM₁) aerosols. Crustal material from both desert dust and road traffic dust resuspension contributed as much as 24 % of the total PM₁ mass (rising to 66 % during desert dust events), a figure not commonly observed in urban environments. Our observations showed significant decreases in black carbon concentrations and ammonium sulfate compared to data from 15 years ago, indicating an important reduction in both local and regional emissions as a result of effective mitigation measures. The diurnal variability of carbonaceous aerosols was attributed to emissions emanating from local traffic at rush hours and nighttime open biomass burning. Surprisingly, semi-volatile ammonium chloride (NH₄Cl) originating from local open biomass and waste burning was found to be the main chemical species in PM₁ over Cairo. Its nighttime formation contributed to aerosol water uptake during morning hours, thereby playing a major role in the build-up of urban haze. While our results confirm the persistence of a significant dust reservoir over Cairo, they also unveil an additional source of highly hygroscopic (semi-volatile) inorganic salts, leading to a unique type of urban haze. This haze, with dominant contributors present in both submicron (primarily as NH₄Cl) and supermicron (largely as dust) modes, underscores the potential implications of heterogeneous chemical transformation of air pollutants in urban environments.

Keywords: Ammonium Chloride; Greater Cairo; Hygroscopic aerosols; Megacity; Submicron aerosols; Urban haze.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Aerosols* / analysis
Air Pollutants* / analysis
Air Pollution* / statistics & numerical data
Cities
Dust / analysis
Egypt
Environmental Monitoring*
Particle Size
Particulate Matter* / analysis

Substances

Aerosols
Air Pollutants
Particulate Matter
Dust