Recycling concrete: An undiscovered source of ultrafine particles

- Ultrafine particle (UFP) emission from simulated concrete recycling process assessed.
- UFP decay profiles around source and associated exposure determined.
- Effectiveness of commonly deployed masks at construction sites analysed.
- Over 90% of particle number concentrations were found in UFP size range.
- UFPs showed much slower decay rate compared with particles >100 nm in diameter.

While concrete recycling is practiced worldwide, there are many unanswered questions in relation to ultrafine particle (UFP; Dp < 100 nm) 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 between 0.15 and 15.15 m that were generated by an experimentally 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 in the 100-560 nm size range. 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.

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