Quantification of an atmospheric nucleation and growth process as a single source of aerosol particles in a city

摘要

Effects of a new aerosol particle formation (NPF) and particle diametergrowth process as a single source of atmospheric particle numberconcentrations were evaluated and quantified on the basis of experimentaldata sets obtained from particle number size distribution measurements in thecity centre and near-city background of Budapest for 5 years.Nucleation strength factors for a nucleation day (NSF) and for ageneral day (NSF) were derived separately for seasons and fullyears. The former characteristic represents the concentration increment ofultrafine (UF) particles specifically on nucleation days with respect toaccumulation-mode (regional background) concentrations (particles withequivalent diameters of 100–1000 nm; ) due solely to thenucleation process. The latter factor expresses the contribution ofnucleation to particle numbers on general days; thus, it represents a longertime interval such as season or year. The nucleation source had the largesteffect on the concentrations around noon and early afternoon, as expected.During this time interval, it became the major source of particles in thenear-city background. Nucleation increased the daily mean concentrations onnucleation days by mean factors of 2.3 and 1.58 in the near-city backgroundand city centre, respectively. Its effect was largest in winter, which wasexplained by the substantially lower levels on nucleation daysthan those on non-nucleation days. On an annual timescale, 37 % of the UFparticles were generated by nucleation in the near-city background, while NPFproduced 13 % of UF particles in the city centre. The differences amongthe annual mean values, and among the corresponding seasonal mean values,were likely caused by the variability in controlling factors from year toyear. The values obtained represent the lower limits of the contributions.The shares determined imply that NPF is a non-negligible or substantialsource of particles in near-city background environments and even in citycentres, where the vehicular road emissions usually prevail. Atmosphericresidence time of nucleation-mode particles was assessed by a decay curveanalysis, and a mean of 02:30 was obtained. The present study suggests thatthe health-related consequences of the atmospheric NPF and growth process incities should also be considered in addition to its urban climateimplications.