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Observations of Wintertime Aerosol Hygroscopicity and Volatility in Budapest

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Title: Observations of Wintertime Aerosol Hygroscopicity and Volatility in Budapest
Author(s): Enroth, Joonas
Contributor: University of Helsinki, Faculty of Science, Department of Physics
Language: English
Acceptance year: 2016
Atmospheric aerosols are liquid or solid particles suspended in the air. These particles are highly relevant for human health as well as the global climate. One of the methods which aerosol particles can affect the climate is by acting as seeds for cloud droplet formation, i.e. cloud condensation nuclei. The formation of the cloud droplets depends on the ambient conditions, but also on the particle properties. In order to estimate the impact of aerosols on the climate, information about the affinity of particles to uptake water is needed. The aim of this work was to provide that information from Budapest, and in eastern Europe more generally as a part of university cooperation between the University of Helsinki and the local Eötvös Loràn University. In this work the hygroscopic and volatile properties of urban atmospheric aerosols was measured in the city center of Budapest, Hungary, using a Hygroscopicity Volatility Tandem Differential Mobility Analyzer. The studied particle sizes were 20, 50, 75, 110 and 145 nm particles and the hygroscopicity and volatility was determined at 90 % RH and 270 °C, respectively. The measurement campaign took place in the winter of 2014-2015. The atmospheric aerosols at Budapest were found to be strongly influenced by local emission sources, most notably by traffic. The aerosol particles were highly externally mixed, and thus separated into two different types. The first type represented the local emissions and this was found to match the traffic pattern well. These particles were more prevalent in the smaller, sub 100 nm, particle size range, and showed only little hygroscopic or volatile properties. The second type was the regional particles, which were found to be more hygroscopic and more volatile. These particles conversely the dominant mode in the larger, plus 100 nm, particle size range. The overall aerosol hygroscopicity was found to be slightly lower at Budapest than at previous urban studies across Europe. This might be explained by the aerosol properties at Budapest differing from those in central Europe, but also by the measurement site of this campaign. The measurement site here was located in the city center rather than in the suburban areas as in most similar studies. The location was also reflected in the strong diurnal variation in the particle hygroscopicity and volatility, as there was also strong variation in the traffic density. This work succeeded in describing the wintertime conditions of hygroscopicity and volatility in Budapest. The results, tough describe only two months of wintertime conditions. In order to know the annual variation, and to describe the conditions more accurately, further measurements are suggested in the form of a campaign in the summer months.

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