Interpretation of particle number size distribution, ultrafine particles and black carbon concentrations in Istanbul

This study is the first to investigate atmospheric nanoparticles in Turkiye, specifically in Istanbul. Total particle number concentrations (PNC) in the 10-400 nm size range were measured at the traffic, suburban and urban background sites, across all seasons in 2023-2024. Simultaneous measurements of black carbon (BC) and other criteria air pollutants were also conducted. The annual average PNCs reached approximately 6000 #/cm³, 8000 #/cm³, and 20,000 #/cm³ at the suburban, urban background and traffic sites, respectively. Ultrafine particles (UFPs, 10-100 nm) contributed an average of 76 % to PNCs at the suburban background, 83 % at the urban background and 89 % at the traffic sites. The particle number size distributions (PNSD) are characterised by a large Aitken mode, and relatively low Nucleation mode contributions when compared with numerous urban-European measurements. The suburban and urban background concentrations of Istanbul and Athens, both representing urban environments in the Eastern Mediterranean, have relatively low nucleation contributions to UFP. For the same period, high (compared with urban Europe) average e-BC concentrations reached 2.4, 3.2, and 6.0 μg/m³, respectively. Thus, compared to the suburban background, PNC and e-BC levels were around 3-fold higher at the traffic site and 1.5-fold higher at the urban background site. A moderate correlation (∼0.6) was found between UFP and e-BC concentrations, whereas weaker correlations (ranging from 0.27 to 0.45) were observed between UFP and PM₁₀ or PM_2.5 across all sites. These findings reveal the similarity between PNC and PNSD patterns in Eastern Mediterranean cities, emphasising the significance of UFPs in Istanbul's atmosphere and supporting the recommendation for continuous monitoring of UFPs and BC.