Low-Cost Black Carbon Detection from Beta Attenuation Monitors Using Image Reflectance Based Method

ABHISHEK ANAND, Albert Presto, Suryaprakash Kompalli, Eniola Ajiboye, Carnegie Mellon University

     Abstract Number: 470
     Working Group: Instrumentation and Methods

Abstract
Exposure to ambient air pollution accounts for 4.2 million deaths annually. Yet, air quality information is inadequate in many densely populated lands for evidence-based policymaking, especially in the Global South. A critical need is better quantification of fine particulate matter (PM_2.5) composition, which can in turn be used to identify crucial pollutant sources. A major barrier is the high capital and operational costs of research-grade monitors. This study investigates a cost-effective way to leverage existing monitors to expand the limited air quality dataset in these areas. The US Department of State collects air pollutant data at US Embassies around the world to inform US personnel and citizens of air quality overseas. These measurements use Beta Attenuation Monitors (BAMs) to measure hourly ambient PM_2.5 concentrations. BAMs collect PM_2.5 onto a filter tape and estimate particle concentrations by measuring attenuation of beta rays using the Beer-Lambert law. We utilize these BAM tapes to determine hourly ambient black carbon (BC) concentration. Each filter tape spot is individually photographed with a cell phone camera on a reference card containing a set of predefined grayscales corresponding to different BC concentrations. The image is then processed through a custom computer-vision Python script, which performs spatial correction, adjusts for lighting variations, locates the filter spot and then compares its red-light reflectance with that of the grayscales on the reference card to estimate BC concentration. The method was calibrated using filters with known BC concentrations determined from co-located aethalometer and offline thermal-optical EC measurements. The limit of detection is approximately 0.2 µg.m^-3 for 1-hr samples. This presentation will show validation of BC estimates from BAM tapes with EC at a US EPA’s Chemical Speciation Network site in Pittsburgh, and analysis of BAM tapes collected at the US Embassies in Addis Ababa, Ethiopia, Abidjan, and Côte d’Ivoire.