Continuous Monitoring of Lung Deposited Surface Area (LDSA) Across 11 European Cities: First Results from the Net4Cities Project

Ultrafine particles (UFPs; <100 nm) represent a significant environmental health challenge, particularly within the transport sector. Traditional mass-based metrics used to monitor particulate matter emissions (PM₁₀​, PM_2.5​) poorly capture the impact of UFPs, which contribute only negligibly to mass but dominate in number and need to be addressed¹. While Particle Number Concentration (PNC) has long been the primary metric for quantifying UFP exposure², Lung Deposited Surface Area (LDSA) has emerged as a valuable complementary metric for a more robust health risk assessment. This metric is biologically vital because the particle surface is the primary interface for toxicological interactions and the generation of oxidative stress within human tissue³.

Despite its high relevance as a proxy for potential health impact, there is currently a significant lack of harmonized data on LDSA immissions and a scarcity of long-term measurements across diverse urban environments. To address this gap, an extensive monitoring network has been established under the Horizon Europe Net4Cities project⁴. Spanning 11 European cities, this network utilizes specifically developed measurement devices based on diffusion charging⁵, enabling continuous 24/7 online monitoring of LDSA concentrations. The strategic deployment of these devices at different site types—namely road traffic hubs, airports, and ports—allows for a detailed comparative assessment and of how various transport activities contribute to local LDSA levels. 

Our preliminary results confirm a high degree of spatiotemporal heterogeneity in LDSA concentrations, a characteristic previously identified in smaller-scale studies^3,6, and demonstrate that these fluctuations are strongly coupled with local human activity across all site types. While road traffic contributes to a consistent diurnal baseline, sites near airports exhibit extreme concentration spikes coinciding with the onset of air traffic, often exceeding peak levels found in heavy road-traffic zones. These findings highlight the importance of LDSA in capturing high-intensity exposure events and provide the robust, multi-city dataset required to support targeted "Zero Pollution" policy interventions in Europe.

 

References: 

(1)         Directive (EU) 2024/2881 of the European Parliament and of the Council of 23 October 2024 on Ambient Air Quality and Cleaner Air for Europe (Recast); 2024. http://data.europa.eu/eli/dir/2024/2881/oj (accessed 2026-01-09).

(2)         WHO global air quality guidelines: particulate matter (PM2.5 and PM10), ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide: executive summary. https://iris.who.int/items/2f8fec42-5636-4506-9b44-e0c91c678484 (accessed 2026-01-09).

(3)         Yuan, J.; Zhang, W.; Hu, J.; Rupakheti, M.; Rupakheti, D. Studies on Lung-Deposited Surface Area (LDSA) of Particulate Matter during 2005–2024. Air Qual. Atmosphere Health 2025, 18, 2431–2446. https://doi.org/10.1007/s11869-025-01786-5.

(4)         Partner Cities – Net4Cities. https://www.net4cities.eu/partnercities/ (accessed 2026-01-09).

(5)         Fierz, M.; Meier, D.; Steigmeier, P.; Burtscher, H. Aerosol Measurement by Induced Currents. Aerosol Sci. Technol. 2014, 48 (4), 350–357. https://doi.org/10.1080/02786826.2013.875981.

(6)         Edebeli, J.; Spirig, C.; Fluck, S.; Fierz, M.; Anet, J. Spatiotemporal Heterogeneity of Lung-Deposited Surface Area in Zurich Switzerland: Lung-Deposited Surface Area as a New Routine Metric for Ambient Particle Monitoring. Int. J. Public Health 2023, 68, 1605879. https://doi.org/10.3389/ijph.2023.1605879.