Black Carbon Measurements in Multiple Cities of Sub-Saharan Africa with Low Cost Image-Reflectance Method

ABHISHEK ANAND, Albert Presto, Suryaprakash Kompalli, Eniola Ajiboye, Evelyne Toure, Julien Bahino, Sylvain Gnamien, Carnegie Mellon University

     Abstract Number: 296
     Working Group: Identifying and Addressing Disparate Health and Social Impacts of Exposure to Aerosols and Other Contaminants across Continents, Communities, and Microenvironments

Abstract
There is a lack of continuous monitoring of air pollutants in the Global South due to high cost of regulatory monitors. We have developed a low-cost method that utilizes reflected red light from particle deposits on filters to measure black carbon (BC). US embassies around the world use Beta Attenuation Monitors (BAMs) to measure PM_2.5. A BAM collects PM_2.5 on filter tapes every hour as spots and uses beta ray attenuation through each spot to measure hourly PM_2.5. We photograph particle spots on used filter tapes from these existing BAMs at US Embassies one at a time with a custom reference card and then apply an image processing algorithm on the photo to estimate BC concentration for that hour. BC estimates from BAM tapes were validated with elemental carbon at a US EPA’s Chemical Speciation Network site in Pittsburgh. The effective detection limit of the method is approximately 0.15 µg.m^-3 for 1-hr samples. We present 2 months (July-August 2020) of hourly BC concentrations for three cities in Sub-Saharan Africa, including Abidjan (Côte d’Ivoire), Addis Ababa (Ethiopia), and Accra (Ghana). The hourly BC data at the three sites show a clear diurnal pattern of BC with prominent peaks during the morning and evening rush hours on workdays. The average BC for the 2-month period at the Abidjan US embassy was 3.85 µg.m^-3 (weekdays: 3.33 µg.m^-3, weekend: 3.98 µg.m^-3). The hourly PM_2.5 concentrations collected by the Embassy showed a high correlation (R² ~ 0.55) with the estimated BC levels. The average BC to PM_2.5 fraction was estimated to be ~18% during weekdays which dropped to ~15% on weekends. The PM_2.5 composition data, thus acquired, can be crucial in identifying emission sources and help in effective policymaking.