Candle soot: Journey from a pollutant to a functional material

Fabrication and characterization of a novel konjac glucomannan-based air filtration aerogels strengthened by wheat straw and okara.

While concrete recycling is practiced worldwide, there are many unanswered questions in relation to ultrafine particle (UFP; Dp<100nm) emissions and exposure around recycling sites. In particular: 

(i) Does recycling produce UFPs and in what quantities? 

(ii) How do they disperse around the source? 

(iii) What impact does recycling have on ambient particle number concentrations (PNCs) and exposure? 

(iv) How effective are commonly used dust respirators to limit exposure? 

We measured size-resolved particles in the 5-560 nm range at five distances from a simulated concrete recycling source and found that: 

(i) the size distributions were multimodal, with up to ~93% of total PNC in the UFP size range; and 

(ii) dilution was a key particle transformation mechanism.

UFPs showed a much slower decay rate, requiring ~62% more distance to reach 10% of their initial concentration compared with their larger counterparts. Compared with typical urban exposure during car journeys, exposure decay profiles showed up to ~5 times higher respiratory deposition within 10 m of the source. Dust respirators were found to remove half of total PNC; however the removal factor for UFPs was only ~57% of that observed in the 100-560 nm size range. These findings highlight a need for developing an understanding of the nature of the particles as well as for better control measures to limit UFP exposure.

Recycling concrete: An undiscovered source of ultrafine particles

Ultrafine particles (UFP; diameter less than 100 nm) are ubiquitous in urban air, and an acknowledged risk to human health. Globally, the major source for urban outdoor UFP concentrations is motor traffic. Ongoing trends towards urbanisation and expansion of road traffic are anticipated to further increase population exposure to UFPs. Numerous experimental studies have characterised UFPs in individual cities, but an integrated evaluation of emissions and population exposure is still lacking. Our analysis suggest that average exposure to outdoor UFPs in Asian cities is about four-times larger than those in European cities but impacts on human health are largely unknown. This article reviews some fundamental drivers of UFP emissions and dispersion, and highlights unresolved challenges, as well as recommendations to ensure sustainable urban development whilst minimising any possible adverse health impacts.

Ultrafine particles in cities

Filtration performance and loading capacity of nano-structured composite filter media for applications with high soot concentrations

Two proposed quartz fibrous filters with dissimilar solid volume fractions and thicknesses are investigated for their efficiency in removing soot aerosol particles from air. Soot particles are sourced from a candle burning in a chamber, and the tests involve 1.5 h of continuous loading of particles at three different flow rates: 4.5, 8.15 and 9.55 l/min. The fractional efficiency, morphology and pressure drop of both clean and loaded filters are studied using a scanning mobility particle sizer, scanning electron microscope and differential pressure gauge. Both filters have relatively similar levels of efficiency 93% for particle size (100–400 nm) at the lowest flow rate. At higher flow rates, the re-entrainment process effects the filtration efficiency of both filters. At the higher flow rate of 8.15 l/min, the filter with a higher solid volume fraction and thickness shows a higher pressure drop and an efficiency level of 95%. Increasing the flow rate to 9.55 l/min helps to pass the particles with diameters larger than 100 nm through two filters. This phenomenon decreases the fractional efficiency of both filters during the loading time.

Capacity of quartz fibers with high filtration efficiency for capturing soot aerosol particles

The capture efficiency of the small aerosol particle is strongly inﬂuenced by the structure of fibrous layers. This study presents particle deposition and dendrite formation on different arrangements of binary fibers. 2-D numerical simulation is performed using the open source software of OpenFOAM. In the instantaneous filtration of a single fiber, obtained results are in good agreement with the existing model. Results showed that addition of nanofiber to microfiber led to high capture efficiency for the particle size 50nm at the cross arrangement with fibers distance 2µm. When particle gets larger, i.e. 150 nm, binary fibers have higher capture efficiency and pressure drop than the single microfiber at all arrangements, especially for the fibers distance 1.5 µm. Therefore, the good fibers arrangement here seems the cross arrangement with the high capture efficiency, average pressure drop and fibers distance 2 µm.

https://www.ije.ir/article_73209_c6a178ab0939950a445afb6ff85dfe16.pdf

S. Akbarnezhad

Papers

Capacity of quartz fibers with high filtration efficiency for capturing soot aerosol particles

Eulerian Lagrangian Simulation of Particle Capture and Dendrite Formation on Binary Fibers