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 Kigali is 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 almost two times that 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. Vehicular 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.
Highlights
Ambient air pollution, especially fine particulate mass (PM2.5) and ozone (O3), has been associated with premature human mortality (Dockery et al, 1993; Jerrett et al, 2009; Laden et al., 2006)
As most of the Kigali O3 data is from real-time affordable multi-pollutant (RAMP) not collocated at Mugogo, the results presented here for ambient carbon monoxide (CO) and O3 are based on the generalized RAMP (gRAMP) models
We have presented the results of a long-term ground-based monitoring campaign, the first of its kind in Kigali, Rwanda
Summary
Especially fine particulate mass (PM2.5) and ozone (O3), has been associated with premature human mortality (Dockery et al, 1993; Jerrett et al, 2009; Laden et al., 2006). The World Health Organization (WHO) estimates that in 2016, ambient air pollution caused about three thousand deaths in Rwanda (Brauer et al, 2012; WHO, 2018). Such estimates can be uncertain because exposure is inferred from satellite estimates. The situation is similar in many other sub-Saharan African countries (Kalisa et al, 2019; Petkova et al, 2013) This lack of monitoring due to resource limitations hampers scientific understanding of the sources contributing to air pollution in these countries, which is essential to formulating effective environmental management policies
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