Author Correction: The relative contributions of traffic and non-traffic sources in ultrafine particle formations in Tehran mega city

Abstract

Emissions of ultrafine particles (UFPs; diameter < 100 nm) are strongly associated with traffic-related emissions and are a growing global concern in urban environments. This study investigated variations in particle number concentration (PNC) for particles larger than 10 nm across nine monitoring stations in Tehran megacity, to determine the primary versus secondary sources of UFPs. Measurements of NOₓ and PNC were gathered from these urban locations in 2020, while black carbon (BC) concentrations were monitored at two stations. All sites exhibited clear diurnal patterns, with PNC peaking during morning and evening rush hours and strongly correlating with NOₓ levels. PNC values in Tehran were higher than those reported in many other cities, ranging on average from 8.4 × 10³ to 5.7 × 10⁴ cm⁻³. The highest concentrations were recorded at a traffic-dominated site (District 19), while the lowest were observed in a residential area (Punak). At Ray and Sharif stations, estimated contributions from primary (direct emissions) and secondary (formed in atmosphere) sources averaged 67% and 33%, respectively. The findings suggest that reductions in primary emissions could significantly lower overall aerosol concentrations, even in the context of photo-nucleation-driven secondary particle formation.