Quantifying traffic, biomass burning and secondary source contributions to atmospheric particle number concentrations at urban and suburban sites

In this study, we propose a new approach to determine the contributions of primary vehicle exhaust (N-1(ff)), primary biomass burning (N-1(bb)) and secondary (N-2) particles to mode segregated particle number concentrations. We used simultaneous measurements of aerosol size distribution in the 12-600 nm size range and black carbon (BC) concentration obtained during winter period at urban and suburban sites influenced by biomass burning (BB) emissions. As expected, larger aerosol number concentrations in the 12-25 and 25-100 nm size ranges are observed at the urban site compared to the suburban site. However, similar concentrations of BC are observed at both sites due to the larger contribution of BB particles to the observed BC at suburban (34%) in comparison to urban site (23%). Due to this influence of BB emissions in our study area, the application of the Rodriguez and Cuevas (2007) method, which was developed for areas mainly influenced by traffic emissions, leads to an overestimation of the primary vehicle exhaust particles concentrations by 18% and 26% in urban and suburban sites, respectively, as compared to our new proposed approach. The results show that (1) N-2 is the main contributor in all size ranges at both sites, (2) N-1(ff) is the main contributor to primary particles (>70%) in all size ranges at both sites and (3) N-1(bb) contributes significantly to the primary particles in the 25-100 and 100-600 nm size ranges at the suburban (24% and 28%, respectively) and urban (13% and 20%, respectively) sites. At urban site, the N-1(ff) contribution shows a slight increase with the increase of total particle concentration, reaching a contribution of up to 65% at high ambient aerosol concentrations. New particle loination events are an important aerosol source during summer noon hours but, on average, these events do not implicate a considerable contribution to urban particles. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

A new method was proposed to determine the contributions of primary vehicle exhaust and biomass burning particles to aerosol number concentrations, showing differences in particle contributions between urban and suburban sites. Urban sites have higher aerosol number concentrations compared to suburban sites, while biomass burning particles contribute more to black carbon levels in suburban areas. The traditional method used in the study leads to an overestimation of primary vehicle exhaust particles concentrations in both urban and suburban sites.