Modelling of black carbon statistical distribution and return periods of extreme concentrations * Katarzyna Maciejewska a, * , Katarzyna Juda-Rezler a , Magdalena Reizer a , Krzysztof Klejnowski b a Warsaw University of Technology, Faculty of Environmental Engineering, Nowowiejska 20, 00-653 Warsaw, Poland b Institute of Environmental Engineering e Polish Academy of Sciences, M. Sklodowskiej-Curie 34, 41-819 Zabrze, Poland article info Article history: Received 22 July 2014 Received in revised form 16 April 2015 Accepted 25 April 2015 Available online 18 June 2015 Keywords: Atmospheric aerosol Black carbon Statistical modelling Frequency distribution Daily profile Return period Poland abstract Eight datasets of 1-h black carbon (BC) concentrations measured in Warsaw agglomeration (Poland), at urban background and sub-urban sites, and in Racib orz, a small town in Upper Silesia district (regional background site) were analyzed to evaluate BC levels, daily profiles and statistical distributions of con- centrations in Central-Eastern European region. The observed mean levels ranged from 1483 ng m 3 in suburban site during summer to 3358 ng m 3 in regional background site in winter. Observed diurnal patterns were bimodal in the locations dominated by traffic emissions, but unimodal, with elevated evening peak in individually heated residential area. Three theoretical frequency distributions were applied to fit analyzed datasets separately. The lognormal distribution was the most appropriate to represent the middle-range values, while the high concentrations were satisfactorily predicted by the type I two-parameter exponential distribution which was used to estimate the return periods of extreme concentrations for winter months. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Atmospheric aerosols play fundamental role in the functioning of the Earth system, and their load have been included as one out of nine major processes within the framework of planetary bound- aries which define a safe operating space for humanity, based on the intrinsic biophysical processes which regulate the stability of the Earth system (Rockstr€ om et al., 2009; Steffen et al., 2015). At- mospheric aerosols have well-known, serious human health im- pacts, leading to about 3.7 million deaths per year (WHO, 2014), as well as a broad spectrum of effects on the climate of the Earth and functioning of the planet's system. One of the most important components of the atmospheric aerosol is carbonaceous matter of natural and anthropogenic origin, which can be primary or sec- ondary and contain both inorganic and organic carbon (OC) species. Due to its distinct properties and extensive range of effects, at- mospheric carbonaceous matter e and black carbon (BC) in particular e is a subject of various research fields, such as climate change, air chemistry, ambient air quality, biogeochemistry, as well as paleoclimatology. Among such a wide group of researchers, it has been difficult to agree on a clear, unambiguous terminology con- cerning quantification of carbonaceous matter. Therefore, Petzold et al. (2013) have lately proposed a consistent terminology, based on the carbonaceous material properties and associated measure- ment techniques and instruments. According to this recommen- dation, ‘soot’ is a qualitative term tightly related to the source of emission of carbonaceous matter, and denotes carbonaceous par- ticles formed from incomplete combustion of carbon-based fuels, i.e. fossil fuels, as well as biofuels and biomass. Two main mea- surement techniques are used to determine the ambient concen- trations of inorganic carbonaceous pollutants, and these are the filter-based light absorption (optical) method whose results are referred to as BC, and the thermal-optical method which provides measurements expressed as elemental carbon (EC). According to the strict definition, BC is the ideally light- absorbing pollutant, refractory and insoluble in water and organic solvents, which is composed of aggregates of small carbon spher- ules that consist mostly of graphite-like sp2-bonded carbon atoms (Petzold et al., 2013). However, such definition is not useful in practice, as carbonaceous matter in the atmosphere is never a pure matter, but a mixture of various carbonaceous compounds of * Thematic Issue on the Modelling Health Risks. * Corresponding author. Tel.: þ48 22 234 72 74. E-mail address: katarzyna.maciejewska@is.pw.edu.pl (K. Maciejewska). Contents lists available at ScienceDirect Environmental Modelling & Software journal homepage: www.elsevier.com/locate/envsoft http://dx.doi.org/10.1016/j.envsoft.2015.04.016 1364-8152/© 2015 Elsevier Ltd. All rights reserved. Environmental Modelling & Software 74 (2015) 212e226