X-Ray Detector Window Importance in the Characterization of Black Carbon Nanoparticles

WILLIAM NICOLAS BACCA NOVOA, Cristina Cordoba, Cesar Diaz Pomar, Cristian Arango, Universidad Distrital Francisco José de Caldas

     Abstract Number: 382
     Working Group: Carbonaceous Aerosols

Abstract
Black Carbon Nanoparticles (BCNs) in the atmosphere are hazardous pollutants that cause severe consequences to human health and the environment. Epidemiological studies directly link chronic exposure to BCNs with respiratory diseases and cardiovascular morbidity, contributing to reduced life expectancy in polluted regions [1]. BCNs are also effective at absorbing solar radiation heating the surrounding air, and reducing albedo accelerating ice melting.

BCNs are especially prevalent in developing nations like Colombia, where urban transit systems remain heavily dependent on diesel-powered vehicles. While local governments have introduced mitigation strategies—such as Bogotá’s electric bus fleet and stricter emissions standards—critical gaps persist [2]. Notably, there remains a characterization deficit in BCN monitoring (e.g., size-resolved abundance, mixing state), hindering the development of targeted policies to reduce their health and climate impacts during the transition to cleaner energy and transportation systems.

Methods for collecting black carbon nanoparticles (BCNs) from the atmosphere based on simple teflon and quartz filters are widely available and cost efficient, however they may constrain the kind of studies that one is able to perform. Typical studies of BCNs deposited on there substrates commonly employ Raman spectroscopy (RS) and scanning electron microscopy (SEM). In SEM-based analyses, the oxygen-to-carbon (O/C) ratio is frequently characterized as a proxy for particle oxidation state, often measured via energy-dispersive Xray spectroscopy (EDS). While both techniques are widely available as standard tools for material characterization, we identified a critical gap in the literature: the lack of systematic studies evaluating how the detector window material (beryllium, polymer-based) in SEM-EDS systems affects the accuracy of O/C ratio quantification for BCNs. This parameter is particularly crucial for low-Z element (C, O) detection, where window absorption properties may introduce significant measurement biases. We provide correction factors for each window and compare the results with newer windowless detectors using BCNs collected on quartz from various areas of Bogota-Colombia.

References:
[1] WHO (2021). Global Air Quality Guidelines.
[2] IDEAM (2022). National Air Quality Report.