A cellphone based system for large-scale monitoring of black carbon

• Published in: Atmospheric environment (1994) 2011-08, Vol.45 (26), p.4481-4487
• Main Authors: Ramanathan, N., Lukac, M., Ahmed, T., Kar, A., Praveen, P.S., Honles, T., Leong, I., Rehman, I.H., Schauer, J.J., Ramanathan, V.
• Format: Article
• Language: English
• Subjects: Aerosols; air; air pollution; Applied sciences; atmospheric chemistry; Atmospheric pollution; Black carbon monitoring; Carbon; Cell phones; Cellphone sensing; climate; climate change; climate models; color; cost effectiveness; Exact sciences and technology; image analysis; issues and policy; Monitoring; Pollution; quartz; reflectance; Rural; rural areas; Soot sensor; Southern California; temporal variation; wavelengths
• ISSN: 1352-2310; 1873-2844
• DOI: 10.1016/j.atmosenv.2011.05.030

Black carbon aerosols are a major component of soot and are also a major contributor to global and regional climate change. Reliable and cost-effective systems to measure near-surface black carbon (BC) mass concentrations (hereafter denoted as [BC]) globally are necessary to validate air pollution and climate models and to evaluate the effectiveness of BC mitigation actions. Toward this goal we describe a new wireless, low-cost, ultra low-power, BC cellphone based monitoring system (BC_CBM). BC_CBM integrates a Miniaturized Aerosol filter Sampler (MAS) with a cellphone for filter image collection, transmission and image analysis for determining [BC] in real time. The BC aerosols in the air accumulate on the MAS quartz filter, resulting in a coloration of the filter. A photograph of the filter is captured by the cellphone camera and transmitted by the cellphone to the analytics component of BC_CBM. The analytics component compares the image with a calibrated reference scale (also included in the photograph) to estimate [BC]. We demonstrate with field data collected from vastly differing environments, ranging from southern California to rural regions in the Indo-Gangetic plains of Northern India, that the total BC deposited on the filter is directly and uniquely related to the reflectance of the filter in the red wavelength, irrespective of its source or how the particles were deposited. [BC] varied from 0.1 to 1 μg m −3 in Southern California and from 10 to 200 μg m −3 in rural India in our field studies. In spite of the 3 orders of magnitude variation in [BC], the BC_CBM system was able to determine the [BC] well within the experimental error of two independent reference instruments for both indoor air and outdoor ambient air. Accurate, global-scale measurements of [BC] in urban and remote rural locations, enabled by the wireless, low-cost, ultra low-power operation of BC_CBM, will make it possible to better capture the large spatial and temporal variations in [BC], informing climate science, health, and policy. ► Low-power, low-cost cellphone system for black carbon monitoring (BC_CBM) described. ► Cellphone captures and uploads images of filters exposed to ambient aerosols. ► Field results show filter color is uniquely related to quantity of BC on filter. ► BC_CBM accuracy within experimental error of 2 reference methods. ► Field accuracy demonstrates BC_CBM potential for large-scale BC monitoring.