A Tale of Two Cities' Black Carbon Measurement

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Source: Enviro Technology Services plc

Advanced photoacoustic measurement of black carbon particles, using equipment available via UK-based Enviro Technology, has led to a better understanding of pollution in Los Angeles and Mexico City.

PAX (Photoacoustic Extinctiometer) Black Carbon Monitors have been deployed to deliver a more accurate picture of daily black carbon trends in these two similarly densely-populated cities. The equipment measures the light absorption of black carbon particles while they are suspended in the air and produces a corresponding sound wave. The intensity of the sound is directly proportional to the level of black carbon currently in the air. 

Monitors in Los Angeles and Mexico City demonstrated quite different weekend and weekday trends. Los Angeles had higher concentrations on weekends, whereas Mexico City had much higher concentrations during the week. Overall, Mexico City’s daily peak values were double those of Los Angeles, but hourly maximum values were similar, reaching almost 10µg m-3.

The differences can be clearly attributed to contrasts in meteorology and traffic patterns, particularly wind patterns and the percentage of diesel-burning vehicles on the road.

Duncan Mounsor, Director of Sales at emissions monitoring specialist Enviro Technology believes important lessons can be learnt from the studies. 

“The data from the two cities paints a clear picture of how urban activity impacts on black carbon levels on a daily and hourly basis,” he explains. “It makes a strong case for photoacoustic monitoring. The accuracy and immediacy of the PAX system’s measurement enables more precisely targeted air pollution management.”

Traditional monitoring of black carbon involves the collection of atmospheric aerosols on a sheet of filter medium, followed by measurement in the change in light intensity while the particles are deposited. The reduction in light is then correlated with the concentration of black carbon in the air. However, there are uncertainties present with filter techniques which photoacoustic methods can overcome. In addition, the equipment can be easily and accurately calibrated in the field.

Mounsor concludes: “We took a long hard look at instrumentation that is currently available for the measurement of black carbon in ambient air and we are delighted to have settled on the PAX from Droplet Technologies. The PAX really is a cutting-edge instrument, and there is no doubt that its photoacoustic extinctiometer technique improves greatly on traditional filter tape instruments.”

Black carbon exists as particles in the atmosphere and is a major component of soot. It has a significant impact on human health and climate change. Scientific evidence and new analyses demonstrate that control of black carbon particles through rapid implementation of proven emission reduction measures would have immediate and multiple benefits for human wellbeing.

The PAX is available exclusively through Enviro Technology in the UK and Ireland. Further information about Enviro Technology is available at: www.et.co.uk

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