| Popis: |
Elevated ambient concentrations of sub-3 nm particles (nanocluster aerosol, NCA) are generally related to atmospheric new particle formation events, usually linked with gaseous sulfuric acid (H2SO4) produced via photochemical oxidation of sulfur dioxide. According to our measurement results of H2SO4 and NCA concentrations, traffic density, and solar irradiance at an urban traffic site in Helsinki, Finland, the view of aerosol formation in traffic-influenced environments is updated by presenting two separate and independent pathways of traffic affecting the atmospheric NCA concentrations: by acting as a direct nanocluster source, and by influencing the production of H2SO4. As traffic density is frequently correlated with solar radiation, it is likely that the influence of traffic-related nanoclusters has been hidden in the diurnal variation, and is thus underestimated because new particle formation events also follow the diurnal cycle of sunlight. Urban aerosol formation studies should, therefore, be updated to include the proposed formation mechanisms. Additionally, the directly emitted NCA poses a potentially elevated health risk, highlighting the need for quantifying the source and loadings in populated areas. The formation of H2SO4 in urban environments is here separated in two routes: primary H2SO4 is formed in hot vehicle exhaust and is converted rapidly to particle phase; secondary H2SO4 results from the combined effect of emitted gaseous precursors and available solar radiation. |
