Source apportionment of ultrafine particle size distributions in urban Europe
Authors: Garcia Marlès Meritxell , Alastuey Andrés , Querol Xavier , Hopke Philip K. 
Published: February 2023

Ultrafine particles (UFP, particles sized <100 nm) &#160;significantly impact health and the environment. However, their study is still a challenge, and a specific regulation is required. The measurement of UFP-PSD (Ultrafine Particles &#8211; Particle Size Distribution) and its application in air quality assessment is a significant goal of RI-URBANS. 2017-2019 hourly UFP-PSD data from 26 sites in urban Europe and one site in the US have been compiled and evaluated according to the instrumental and methodological approaches implemented; the comparison of urban concentrations across Europe; the identification of similarities and major differences; and the evaluation of relationships with other pollutants, such as BC, PMx and gaseous pollutants (SO2, NOx, O3, CO), and with meteorological parameters. The results of this study have recently been published by Trechera et al. (2023).To continue the study by Trechera et al. (2023) in UFP, source apportionment for the previous 27 urban sites is being analyzed with an extended period from 2009 to 2019. This study aims to identify and quantify sources contributing to UFP-PSD using Positive Matrix Factorization (PMF), comparing the differences between the sites. PMF is a widely used multivariate factor analysis tool to identify the source types that may be contributing to the sample using measured source profile information. According to a recent review on UFP source apportionment based on UFP-PSD measurements by Hopke et al. (2022), the typically reported sources of UFP include nucleation, several traffic sources (fresh to aged), domestic and residential heating, regional secondary inorganic aerosols (i.e., regional nitrate and sulfate), particles associated with oxidants as represented by O3 (i.e., regional secondary organic and inorganic aerosols) and other sources (such as biomass burning, urban background sources, industrial emissions, diverse sources, dust and unknown sources). In the near future we expect to publish the results of source apportionment for the datasets mentioned above.&#160;&#160;&#160;&#160;&#160;&#160;Cassee F., Morawska L., Peters A. (Eds)., 2019. The White Paper on Ambient Ultrafine Particles: evidence for policy makers. &#8216;Thinking outside the box&#8217; Team, October 2019, 23 pp, https://efca.net/files/WHITE%20PAPER-UFP%20evidence%20for%20policy%20makers%20(25%20OCT).pdfHopke, P.K., Feng, Y., Dai, Q., 2022. Source apportionment of particle number concentrations: A global review. Sci. Total Environ. 819, 153104. https://doi.org/10.1016/j.scitotenv.2022.153104Paatero, P., and U. Tapper, 1994. Positive matrix factorization: A non-negative factor model with optimal utilization of error estimates of data values., Environmetrics, 5, 111&#8211;126, doi:10.1002/env.3170050203Rivas, I., Vicens, L., Basaga&#241;a, X., Tob&#237;as, A., Katsouyanni, K., Walton, H., H&#252;glin, C., Alastuey, A., Kulmala, M., Harrison, R.M., Pekkanen, J., Querol, X., Sunyer, J., Kelly, F.J., 2021. Associations between sources of particle number and mortality in four European cities. Environ. Int. 155. https://doi.org/10.1016/j.envint.2021.106662Trechera, P., Garcia-Marl&#232;s, M., Liu, X., et al., 2023. Phenomenology of ultrafine particle concentrations and size distribution across urban Europe. Environ. Int. Accepted (Publication in progress).