Estimate of main local sources to ambient ultrafine particle number concentrations in an urban area

Highlights • Novel statistical model apportions source of particle number concentration (PNC). • Nucleated particles play a dominant role in increasing concentrations of urban PNC. • Mid-day PNC was up to 32% higher than corresponding peak traffic hours. • The majority of mid-day PNC were below 30 nm in diameter. Abstract Quantifying and apportioning the contribution of a range of sources to ultrafine particles (UFPs, D 2.5, PM10, NOx, CO, meteorological parameters and traffic counts at a stationary monitoring site. The developed Bayesian model showed reliable predictive performances in quantifying the contribution of NP formation events to UFPs (up to 4 × 104 particles cm− 3), with a significant day to day variability. The model identified potential NP formation and no-formations days based on PNC data and quantified the sources contribution to UFPs. Exploratory statistical analyses show that total mean PNC during the middle of the day was up to 32% higher than during peak morning and evening traffic periods, which were associated with NP formation events. The majority of UFPs measured during the peak traffic and NP formation periods were between 30–100 nm and smaller than 30 nm, respectively. To date, this is the first application of Bayesian model to apportion different sources contribution to UFPs, and therefore the importance of this study is not only in its modelling outcomes but in demonstrating the applicability and advantages of this statistical approach to air pollution studies