First measurements of PM2.5 and NO2 in Mombasa, Kenya

In Africa, air pollution causes an estimated 780,000 premature deaths annually, and a significant number of diseases (comorbidities) that are known to be worsened by chronic exposure to air pollution, like asthma, lung cancer, and chronic obstructive pulmonary disease (COPD). Five hundred million African children live in areas with no reliable air quality monitoring, making actual impacts uncertain. Many major cities have limited or non-existent air quality monitoring networks. One such city with limited monitoring includes Mombasa, a major port city in Kenya with a population of at least 1.2 million people and growing. To address this lack of air pollution data, we deploy a reference Beta Attenuation Monitor 1022 (BAM-1022) and four Clarity Node-S low cost sensors in diverse environments within Mombasa. Locations include 2 urban sites on the main Mombasa island, one residential site, and one site in proximity to Bamburi Cement Factory, a major point source slightly north of the city. Low-cost PM2.5 from the Clarity Node-S are calibrated against the reference BAM-1022 and yield high correlation on daily and hourly timescales but moderate bias. Initial results show relatively good air quality for the months of July (~10 µg m-3 average) at the urban and residential sites, perhaps modulated by pristine air mixing in from the Indian Ocean. Concentrations at the industrial cement site are significantly elevated, with a July average of ~13 µg m-3 and peak hourly concentrations reaching 70 µg m-3. Nonetheless, these air pollution levels are surprisingly low for a major city with a variety of emissions sources, and substantially lower than July mean levels in Nairobi which are about 23 µg m-3 in urban environments. NO2 concentrations in Mombasa are also low, at only about 13 ppbv compared to 16 ppbv in Nairobi, though better understanding and characterization of low-cost NO2 sensors are needed before placing high confidence in this data. Ongoing work will examine additional data as it comes in and attempt to understand sources and explanations for the relatively cleaner air quality in Mombasa.