Traffic, marine ships and nucleation as the main sources of ultrafine particles in suburban Shanghai, China

Abstract

The health effects associated with ultrafine particles (UFPs) have received significant attention. Precisely identifying the sources of UFPs and quantifying their contributions pose considerable challenges. In this study, simultaneous observations were conducted at two suburban sites in Shanghai, a megacity in China, to measure the particle number size distributions (PNSD) and investigate the characteristics of UFPs. The application of the non-negative matrix factorization (NMF) algorithm on PNSD determines 5 factors at each site. The sources of UFPs are very different between the inland (Dianshan Lake, DSL) site and the seacoast (Dongtan, DT) site. By analyzing size distributions and daily variations of resolved factors, and examining their relationships with criteria pollutants and PM_2.5 (particulate matter with diameters ≤2.5 μm) chemical compositions, we identify the main sources of UFPs. At the DSL site, fresh and aged traffic emissions and traffic nucleation are the main contributors to UFPs. At the DT site, photochemical nucleation and growth processes and marine ship emissions are the most important UFP sources. Industrial emissions and the regional background are characterized by a larger GMD (geometric mean diameter) and contribute more to particle volume concentrations (PVC) rather than particle number concentrations (PNC), indicating their association with PM_2.5 rather than UFPs. These findings emphasize the underlying reasons why UFPs and PM_2.5 belong to two different metrics. Concerning the respiratory deposition of particles, the main UFPs sources also pose the greatest health risk. Either during clean days (PM_2.5 < 35 μg m⁻³) or during polluted days (PM_2.5 > 35 μg m⁻³), PNC_Deposits only varies slightly. And photochemical nucleation (i.e., new particle formation events) can significantly increase PNC deposited in the respiratory system.