Air pollution in Kigali, Rwanda: spatial and temporal variability, source contributions, and the impact of car-free Sundays

  • R Subramanian Carnegie Mellon University
  • Abdou Safari Kagabo 3Department of Physics, University of Rwanda, Kigali, Rwanda
  • Valérien Baharane Department of Physics, University of Rwanda, Kigali, Rwanda
  • Sandrine Guhirwa Department of Physics, University of Rwanda, Kigali, Rwanda
  • Claver Sindayigaya Department of Physics, University of Rwanda, Kigali, Rwanda
  • Carl Malings Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA 15218, USA , Observatoire Sciences de l’Univers-Enveloppes Fluides de la Ville à l’Exobiologie, CNRS UMS3563, France, NASA Postdoctoral Program Fellow, Goddard Space Flight Center, Greenbelt, Maryland, MD 20771, USA https://orcid.org/0000-0002-2242-4328
  • Nathan J Williams Department of Engineering and Public Policy, Carnegie Mellon University, Pittsburgh, PA, USA, Kigali Collaborative Research Center, Kigali, Rwanda https://orcid.org/0000-0002-5676-2288
  • Egide Kalisa Institute for Applied Ecology New Zealand, School of Science, Auckland University of Technology, Auckland 1142, New Zealand https://orcid.org/0000-0001-9906-583X
  • Haofan Li Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA 15218, USA
  • Peter Adams Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA 15218, USA https://orcid.org/0000-0003-0041-058X
  • Allen L Robinson Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA 15218, USA https://orcid.org/0000-0002-1819-083X
  • H. Langley DeWitt Center for Global Change Science, Massachusetts Institute of Technology, Cambridge, MA, USA
  • Jimmy Gasore Department of Physics, University of Rwanda, Kigali, Rwanda, Kigali Collaborative Research Center, Kigali, Rwanda
  • Paulina Jaramillo Department of Engineering and Public Policy, Carnegie Mellon University, Pittsburgh, PA, USA, Kigali Collaborative Research Center, Kigali, Rwanda https://orcid.org/0000-0002-4214-1106
Keywords: fine particulate matter, ozone, black carbon, Sub-Saharan Africa, urban air pollution, vehicular emissions, biofuel emissions, low-cost sensors

Abstract

Ambient air pollution, particularly fine particulate mass (PM2.5) and ozone (O3), is associated with premature human mortality and other health effects, but monitoring is scarce to non-existent in large parts of Africa. Lower-cost real-time affordable multi-pollutant (RAMP) monitors and a black carbon monitor were deployed in Kigali, Rwanda to fill the air quality data gap here. PM2.5 data were corrected using data from a coincident, short-term campaign that used standard filter-based gravimetry, while gas data were verified by collocation with reference carbon monoxide (CO) and O3 monitors at the Rwanda Climate Observatory at Mt Mugogo, Rwanda. Over March 2017-July 2018, the ambient average PM2.5 in Kigali was 52 µg/m3, significantly higher than World Health Organization (WHO) Interim Target 1. Study average BC was 4 µg/m3, comparable to mid-sized urban areas in India and China and significantly higher than BC in cities in developed countries. Spatial variability across various urban background sites in Kigali appears to be limited, while PM2.5 at Mt Mugogo is moderately correlated with PM2.5 in Kigali. A sharp diurnal profile is observed in both PM2.5 and BC, with the Absorption Angstrom Exponent (AAE) indicating that the morning peak is associated with rush-hour traffic-related air pollution (TRAP) while the late evening peak can be attributed to both traffic and domestic biofuel use. PM2.5 in the dry seasons is about two times PM2.5 during the following wet seasons while BC is 40-60% higher. Local sources contribute at least half the ambient PM2.5 during wet seasons and one-fourth during dry seasons. Traffic restrictions on some Sundays appear to reduce PM2.5 and BC by 10-12 µg/m3 and 1 µg/m3 respectively, but this needs further investigation. Dry season ozone in Kigali can exceed WHO guidelines. These lower-cost monitors can play an important role in the continued monitoring essential to track the effectiveness of pollution-control policies recently implemented in Rwanda.

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Published
2020-08-27
Section
Research Article