Abstract
Abstract. Effects of a new aerosol particle formation (NPF) and particle diameter growth process as a single source of atmospheric particle number concentrations were evaluated and quantified on the basis of experimental data sets obtained from particle number size distribution measurements in the city centre and near-city background of Budapest for 5 years. Nucleation strength factors for a nucleation day (NSFNUC) and for a general day (NSFGEN) were derived separately for seasons and full years. The former characteristic represents the concentration increment of ultrafine (UF) particles specifically on nucleation days with respect to accumulation-mode (regional background) concentrations (particles with equivalent diameters of 100–1000 nm; N100−1000) due solely to the nucleation process. The latter factor expresses the contribution of nucleation to particle numbers on general days; thus, it represents a longer time interval such as season or year. The nucleation source had the largest effect on the concentrations around noon and early afternoon, as expected. During this time interval, it became the major source of particles in the near-city background. Nucleation increased the daily mean concentrations on nucleation days by mean factors of 2.3 and 1.58 in the near-city background and city centre, respectively. Its effect was largest in winter, which was explained by the substantially lower N100−1000 levels on nucleation days than those on non-nucleation days. On an annual timescale, 37 % of the UF particles were generated by nucleation in the near-city background, while NPF produced 13 % of UF particles in the city centre. The differences among the annual mean values, and among the corresponding seasonal mean values, were likely caused by the variability in controlling factors from year to year. The values obtained represent the lower limits of the contributions. The shares determined imply that NPF is a non-negligible or substantial source of particles in near-city background environments and even in city centres, where the vehicular road emissions usually prevail. Atmospheric residence time of nucleation-mode particles was assessed by a decay curve analysis, and a mean of 02:30 was obtained. The present study suggests that the health-related consequences of the atmospheric NPF and growth process in cities should also be considered in addition to its urban climate implications.
Highlights
Large-scale modelling studies suggest that the new aerosol particle formation (NPF) and consecutive particle diameter growth process in the atmosphere (Kulmala et al, 2004, 2013) is the dominant source of particle number concentrations on a global scale (Spracklen et al, 2006; Reddington et al, 2011; Makkonen et al, 2012; Yu et al, 2015)
The seasonal variation of the nucleation frequency fits into the second group of measurement sites – which is characterized by the highest number of nucleation events in spring and the lowest in winter, with a relatively high total number of events (Manninen et al, 2010)
We showed in the present study that NPF and a particle diameter growth process as a single source represent a considerable contribution to UF particles in a central European city with respect to all other emission sources, including vehicular road traffic
Summary
Large-scale modelling studies suggest that the new aerosol particle formation (NPF) and consecutive particle diameter growth process in the atmosphere (Kulmala et al, 2004, 2013) is the dominant source of particle number concentrations on a global scale (Spracklen et al, 2006; Reddington et al, 2011; Makkonen et al, 2012; Yu et al, 2015). The share of NPF as a single source of ambient particle number concentrations in cities remained, largely unknown despite the fact that there is often a spatial coincidence between the poorer air quality and population density (Samoli et al, 2016). The maximum values in the city centre represented concentration contributions from 30 to 60 % due to nucleation for a limited time interval. The curve for the near-city background was the largest, as expected, and it even exceeded the value of 2 around noon for approximately 3 h This all means that nucleation has an important contribution to UF particles during the midday in the city centre, while it even becomes the dominant source of particles directly after midday in the near-city background.
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