engleski

Comparison and trends of measured elemental carbon mass concentrations and estimated mass concentrations of black carbon in PM2.5 particle fraction

Black smoke (BS) is a product of incomplete combustion and a pollutant generally present in inhabited zones. It is commonly known as a collection of fine solid and/or liquid particles from several nanometres to several microns. Since the usual sample mass is too small for reliable gravimetrical analysis, optical methods are commonly used for determining its mass concentration. It is of extreme importance that the mass concentration of BS not be confused with that of suspended particles. BS concentrations are determined in order to evaluate the impact on human health, because its composition may cause negative health effects, including carcinogenic ones. The term total carbon (TC) refers to all forms of carbon present in samples of particulate matter in air ; organic (OC), elemental (EC) and carbonate carbon (CC), which derive from fossil fuel combustion, biomass burning, residential space heating coal, biogenic emissions and secondary sources. EC has a long lifetime in the atmosphere and it is a visible component of particulate matter in ambient air. Particulate EC is also defined by collection and analysis. In atmospheric conditions, EC is inert, non-volatile, insoluble in solvents, and absorbs wavelengths from the visible, near infrared and ultraviolet region. It has a large specific surface area and can be a carrier of polluting gases and particles adhered to its surface transporting them deeper into the human respiratory tract. Daily PM2.5 samples were collected continuously during a five-year period, from the beginning of 2014 to the end of 2018. The sampling station was situated in the northern residential part of Zagreb. PM mass concentrations were determined gravimetrically following EN 12341:2014. Samples were analysed for OC and EC using the thermal/optical transmittance method (TOT) with a Quartz protocol. Mass concentrations of BC, instead by aethelometry, were estimated using light absorption coefficient from BS measurements determined by a Smokestain reflectometer EEL43M. This approach allows the estimation of the mass concentration of EC in airborne particles at multiple points without additional expensive and time-consuming analyses. It is necessary to emphasize that the model estimates the distribution parameters of a larger set of data better than individual data. The EC measured and estimated BC mass concentrations in airborne particles were well matched in the PM2.5 fraction of particles collected over the investigated period. The range of the estimated BC mass concentrations was narrower than the range of measured EC concentrations as a result of the absorption coefficient saturation in the range of high concentrations. During the measured period, the results showed a slightly decreasing trend for BC concentrations while no trend was found for EC concentrations. Both BC and EC mass concentrations showed a well- expressed seasonal dependence.

BC, BS, BSI, EC and PM2.5

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