Measurements of sub-3 nm particles using a particle size magnifier in different environments: from clean mountain top to polluted megacities

摘要

The measurement of sub-3 nm aerosol particles is technicallychallenging. Therefore, there is a lack of knowledge about the concentrationsof atmospheric sub-3 nm particles and their variation in differentenvironments. In this study, the concentrations of ∼ 1–3 nm particlesmeasured with a particle size magnifier (PSM) were investigated at nine sitesaround the world. Sub-3 nm particle concentrations were highest at the siteswith strong anthropogenic influence. In boreal forest, measured particleconcentrations were clearly higher in summer than in winter, suggesting theimportance of biogenic precursor vapors in this environment. At all sites, sub-3 nm particle concentrations had daytime maxima, which are likely linkedto the photochemical production of precursor vapors and the emissions ofprecursor vapors or particles from different sources. When comparing ionconcentrations to the total sub-3 nm particle concentrations, electricallyneutral particles were observed to dominate in polluted environments and inboreal forest during spring and summer. Generally, the concentrations ofsub-3 nm particles seem to be determined by the availability of precursorvapors rather than the level of the sink caused by preexisting aerosolparticles. The results also indicate that the formation of the smallestparticles and their subsequent growth to larger sizes are two separateprocesses, and therefore studying the concentration of sub-3 nm particlesseparately in different size ranges is essential.