Sub-23 nm Particles Dominate Non-Volatile Particle Number Emissions of Road Traffic

Abstract

Ultrafine particles (<100 nm) in urban air are a serious health hazard not yet fully understood. Therefore, particle number concentration monitoring was recently included in the WHO air quality guidelines. At present, e.g., the EU regulates particle number only regarding the emissions of solid particles larger than 23 nm emitted by vehicles. The aim of this study was to examine the non-volatile fraction of sub-23 nm particles in a trafficinfluenced urban environment. We measured the number concentration of particles larger than 1.4, 3, 10, and 23 nm in May 2018. Volatile compounds were thermally removed in the sampling line and the line losses were carefully determined. According to our results, the sub-23 nm particles dominated the non-volatile number concentrations. Additionally, based on the determined particle number emission factors, the traffic emissions of non-volatile sub-10 nm particles can be even 3 times higher than those of particles larger than 10 nm. Yet, only a fraction of urban sub-10 nm particles consisted of non-volatiles. Thus, while the results highlight the role of ultrafine particles in the traffic-influenced urban air, a careful consideration is needed in terms of future particle number standards to cover the varying factors affecting measured concentrations.

Inter-Annual Trends of Ultrafine Particles in Urban Europe

“…At present, the EU regulates PNC emissions from vehicles only for those >23 nm. Very recently, Lintusaari et al (2023) showed that the <23 nm particles dominated the non-volatile number concentrations and that the traffic emissions of non-volatile <10 nm particles can be even 3 times higher than those >10 nm. Yet, only a fraction of urban <10 nm particles consisted of non-volatiles.…”

Pushing nano-aerosol measurements to a new decade – Technical note on Airmodus Particle Size Magnifier 2.0

“…Earlier studies have observed a large number of particles in the sub-3 nm size range e.g. in fresh traffic emissions (Rönkkö et al, 2017, Lintusaari et al, 2023, boreal forests (Kulmala et al, 2013, Sulo et al, 2021, polluted environments (Kontkanen et al, 2017, rainforest (Wimmer et al, 2018), arctic environments (Sipilä et al, 2021), mountaintops (Bianchi et al, 2020) as well as industry (Ahonen et al, 2017;Sarnela et al, 2015) and indoor air (Farmer et al, 2019).…”