Black Carbon Sensing
Black carbon (BC) is the light-absorbing portion of particulate matter pollution emitted during the incomplete combustion of fossil fuels or biomass. Common BC sources include diesel vehicles and wood fires. These combustion emissions are harmful to both human health and the environment.
Schematic of Aerosol Absorption Photometer
The ObservAir measures BC using an aerosol absorption photometer (AAP) designed and developed at DSTech. Two fibrous filter spots (3mm in diameter) are mounted to a foam tab that seals in the AAP. Photodiodes monitor the intensity of 880 nm light transmitted from LEDs through the two filters.
As polluted air is drawn through the AAP, light-absorbing BC accumulates on the first ‘signal’ filter and the transmitted light intensity dims predictably over time. Filtered air (devoid of PM) then passes through the second ‘reference’ filter, so it is unaffected by BC concentrations. By comparing the reference light intensity to the signal, it is possible to isolate the light attenuation resulting from BC absorption alone, while eliminating other factors. Using the light attenuation data, BC concentrations are calculated in real-time. The tab is replaced when too much BC has collected on the filter, as the light intensity signal degrades.
New, clean filter
Used, dirty filter