Real world ultrafine particle emission factors for road-traffic derived from multi-year urban flux measurements using eddy covariance

Abstract

Vehicular traffic is an important source of ultrafine particles in urban areas. The emission strength may be quantified using particle emission factors (EF) which are an important input to air-quality models such as dispersion or chemical transport models. We quantified particle EFs for a mixed traffic fleet from size-resolved particle number flux measurements in the size range 10 nm < D_p < 200 nm utilizing the eddy covariance technique at an urban site in Berlin, Germany over the time period from 2017–2020. Particle EFs were calculated using a linear regression approach of particle number fluxes vs. traffic intensity. For the 3 year observation period the average total particle number emission for the mixed fleet was 2.80 × 10¹⁴ veh⁻¹ km⁻¹. The strongest particle emission occurred in the nucleation mode (D_p < 30 nm), i.e. 69% of total mixed fleet particle emission. A multiple regression analysis for light (LDV) and heavy duty vehicles (HDV) indicated higher EF_HDV by a factor of 11.2 for ultrafine particles (D_p < 100 nm) than EF_LDV, and a factor 9.8 for nucleation mode particles. The eddy covariance particle flux measurements proved a powerful approach to quantify size-resolved particle EFs over multiple years.