Nitrocatechols (NCs) are hazardous environmental pollutants that pose a significant risk to aquatic organisms. The toxicity of pollutants is determined by their speciation, which depends on interactions with coexisting inorganic and organic substances, emphasizing the need for detailed specific studies. Employing square wave and cyclic voltammetry, we investigated the complexation between NCs, specifically 4-nitrocatechol (4NC), 3methyl-4-nitrocatechol (3M4NC), 3-methyl-5-nitrocatechol (3M5NC), and 4-methyl-5-nitrocatechol (4M5NC), and copper ions (Cu(II)), a micronutrient that is toxic at elevated concentrations. By confirming and following a quasi-reversible two-electron reduction of di-nitrocatecholate [Cu(NC)2]2- complexes in slightly alkaline solution (pH 8.2), we demonstrated fast complex formation in solution at different analyte concentrations and high kinetic stability. However, the pH lowering resulted in degradation of these complexes, yielding mononitrocatecholate [Cu(NC)] species and eventually uncomplexed Cu(II) ions. The chronic toxicity bioassays (AlgaeTox) with Scenedesmus subspicatus microalgae exposed to a mixture of Cu(II) and NCs at different concentrations showed decreased toxicity compared to the toxicity of individual Cu(II) and NCs. This decrease was linked to the formation of [Cu(NC)2]2- complexes, which was confirmed by the appearance of a corresponding voltammetric reduction peak. Conversely, increased toxicity was observed when the complexes were degraded, resulting in the presence of free/labile Cu(II) or NCs species in the solution. These results demonstrate that concentration-dependent complexation between pollutants significantly alters the toxicity profile of Cu(II)/NC systems. This study highlights the value of voltammetry with a mercury drop working electrode as a reliable method for studying pollutant complexation relevant to ecotoxicity in natural waters.

New particle formation (NPF) is considered a major source of aerosol particles and cloud condensation nuclei (CCN); however, our understanding of NPF and the subsequent particle growth mechanisms in coastal areas remains limited. This study provides evidence of frequent NPF events followed by particle growth in the middle Adriatic Sea during the summer months at the coastal station of Rogoznica in Croatia. To our knowledge, this is the first study to report such events in this region. Our research aims to improve the understanding of NPF by investigating particle growth through detailed physicochemical characterization and event classification. We used a combination of online measurements and offline particle collection, followed by a thorough chemical analysis. Our results suggest the role of bromine in the particle growth process and provide evidence for its involvement in combination with organic compounds. In addition, we demonstrated the significant influence of surface-active substances (SAS) on particle growth. NPF and particle growth events have been observed in air masses originating from the Adriatic Sea, which can serve as an important source of volatile organic compounds (VOC). Our study shows an intricate interplay between bromine, organic carbon (OC), and SAS in atmospheric particle growth, contributing to a better understanding of coastal NPF processes. In this context, we also introduced a new approach using the semi-empirical 1st derivative method to determine the growth rate for each time point that is not sensitive to the nonlinear behavior of the particle growth over time. We observed that during NPF and particle growth event days, the OC concentration measured in the ultrafine mode particle fraction was higher compared to non-event days. Moreover, in contrast to non-event days, bromine compounds were detected in the ultrafine mode atmospheric particle fraction on nearly all NPF and particle growth event days. Regarding sulfuric acid, the measured sulfate concentration in the ultrafine mode atmospheric particle fraction on both NPF event and non-event days showed no significant differences. This suggests that sulfuric acid may not be the primary factor influencing the appearance of NPF and the particle growth process in the coastal region of Rogoznica.

C5- and C6- unsaturated oxygenated organic compounds emitted by plants under stress like cutting, freezing or drying, known as Green Leaf Volatiles (GLVs), may clear some of the existing uncertainties in secondary organic aerosol (SOA) budget. The transformations of GLVs are a potential source of SOA components through photo-oxidation processes occurring in the atmospheric aqueous phase. Here, we investigated the aqueous photo-oxidation products from three abundant GLVs (1-penten-3-ol, (Z)-2-hexen-1-ol, and (E)-2-hexen-1-al) induced by OH radicals, carried out in a photo-reactor under simulated solar conditions. The aqueous reaction samples were analyzed using advanced hyphenated mass spectrometry techniques: capillary gas chromatography mass spectrometry (c-GC-MS); and reversed-phase liquid chromatography high resolution mass spectrometry (LC-HRMS). Using carbonyl-targeted c-GC-MS analysis, we confirmed the presence of propionaldehyde, butyraldehyde, 1-penten-3-one, and 2-hexen-1-al in the reaction samples. The LC-HRMS analysis confirmed the presence of a new carbonyl product with the molecular formula C6H10O2, which probably bears the hydroxyhexenal or hydroxyhexenone structure. Density functional theory (DFT)-based quantum calculations were used to evaluate the experimental data and obtain insight into the formation mechanism and structures of the identified oxidation products via the addition and hydrogen-abstraction pathways. DFT calculations highlighted the importance of the hydrogen abstraction pathway leading to the new product C6H10O2. Atmospheric relevance of the identified products was evaluated using a set of physical property data like Henry's law constant (HLC) and vapor pressure (VP). The unknown product of molecular formula C6H10O2 has higher HLC and lower VP than the parent GLV and thus has potential to remain in the aqueous phase leading to possible aqueous SOA formation. Other observed carbonyl products are likely first stage oxidation products and precursors of aged SOA.

Atmospheric gases and particulate matter (PM) in contact with the material’s surface lead to chemical and physical changes, which in most cases cause degradation of the cultural heritage material. Atmospheric damage and soiling are recognized as two pivotal forms of deterioration of cultural heritage materials caused by air pollution. However, the atmospheric damage effect of PM is rather complicated; its variable composition accelerates the deterioration process. Considering this, one of the important contributions of this work is to review the existing knowledge on PM influence on atmospheric damage, further recognize, and critically evaluate the main gaps in current understanding. The second phenomenon related to cultural heritage material and PM pollution is soiling. Even if soiling was recognized long ago, its definition and knowledge have not changed much for several decades. In the past, it was believed that black carbon (BC) was the primary soiling agent and that the change of the lightness could effectively measure the soiling. With the change of pollution situation, the lightness measurements do not represent the degree of soiling correctly. The additional contribution of this work is thus, the critical evaluation of soiling measurements, and accordingly, due to the change of pollution situation, redefinition of soiling is proposed. Even though numerous studies have treated soiling and atmospheric damage separately, there is an overlap between these two processes. No systematic studies exist on the synergy between soiling and atmospheric damage caused by atmospheric PM.

Air pollution studies are still scarce in some areas in Europe like around the Adriatic Sea. Source apportionment of the fine particulate (PM2.5) organic aerosol (OA) was conducted near Rogoznica, a small touristic settlement on the Eastern Adriatic coast of Croatia, near Lake Rogoznica (43.53° N, 15.95° E). Filter-based offline analyses of PM by a high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and an extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF) were used to apportion OA to its sources. We quantified the contributions of fresh biomass burning OA (BBOA) and three oxygenated OA (OOA), denoted as background OOA (bkgOOA), summer OOA (SOOA), and sulfur-containing OOA (SC-OOA). The bkgOOA component correlates with anthropogenically influenced secondary inorganic aerosol constituents (e.g. sulfate) and dominates OA both during the warm and cold seasons (44%). It exhibits characteristics of regional SOA and there are indications that during the warm season SOA from wildfires could be a substantial contributor. EESI-TOF measurements of the levoglucosan related ion showed a high correlation with the BBOA factor. Secondary OA has a similar molecular composition during the cold and warm seasons – in line with the large contribution of bkgOOA throughout the investigated seasons. SOOA comprises 19% of total OA and increases exponentially with the local temperature, consistent with SOA production by oxidation of biogenic emissions. In addition to biogenic precursors, other precursors (alkanes and aromatic) may contribute to the OOA enhancement during the warm season. SC-OOA is a minor contributor to OA (6%) and is most likely linked to emissions from a close-by marine lake.

Nitroaromatic compounds (NACs) as important constituents of atmospheric humic-like substances (HULIS) and brown carbon (BrC) affect the Earth's climate and pose a serious environmental hazard. We investigated seasonal size-segregated NACs in aerosol samples from the urban background environment in Ljubljana, Slovenia. Total concentrations of twenty NACs in PM15.6 were on average from 0.51 ng m(-3) (summer) to 109 ng m? 3 (winter), and contributed the most to submicron aerosols (more than 74%). Besides 4-nitrocatechol (4NC) as the prevailing species, methylnitrocatechols (MNCs) and nitrophenols (NPs), we reported on some very rarely mentioned, but also on five novel NACs (i.e., 3H4NBA: 3-hydroxy-4-nitrobenzoic acid, 3MeO4NP: 3-methoxy-4nitrophenol, 4Et5NC: 4-ethyl-5-nitrocatechol, 3Et5NC: 3-ethyl-5-nitrocatechol and 3MeO5NC: 3-methoxy-5nitrocatechol). Concentrations of 3MeO5NC, 4Et5NC and 3Et5NC were enhanced during cold seasons, contributing up to 11% to total NAC in winter. In cold season, NAC size distributions were characterized with the peaks in the broader size range of 0.305-1.01 mu m (accumulation mode), with 4NC and alkyl-nitrocatechols ( n-ary sumation (M/Et) NC) as the most abundant, followed by 4-nitrosyringol, nitrophenols and nitroguaiacols. In spring, a pronounced peak of n-ary sumation (M/Et)NC was observed in the accumulation mode (0.305-0.56 mu m) as well as in the coarse one. A strong correlation of all NACs with n-ary sumation (M/Et)NC and levoglucosan indicates that primary emissions of wood burning were the most important source of NACs, but their secondary formation (e.g., aqueous-phase at higher ambient RH) in cold season could also be a significant one. In warmer season, NACs may be mostly derived from traffic-related aromatic VOCs. The contribution of NACs to the light absorption of the aqueous extracts was up to 10-times higher (contribution to Abs365 up to 31%) than their mass contributions to WSOC (up to 3%) of corresponding size-segregated aerosols, confirming that most of the identified NACs are strong BrC chromophores.

Green plants exposed to abiotic or biotic stress release C-5 and C-6 unsaturated oxygenated hydrocarbons called Green Leaf Volatiles (GLVs). GLVs partition into tropospheric waters and react to form secondary organic aerosol (SOA). We explored the kinetics of aqueous-phase reactions of 1-penten-3-ol (PENTOL), (Z)-2-hexen-1-ol (HEXOL), and (E)-2-hexen-1-al (HEXAL) with SO4•–, •OH, and NO3•. At 298 K, the rate constants for reactions of PENTOL, HEXOL, and HEXAL with SO4•– were, respectively, (9.4 ± 1.0) × 108 L mol–1 s–1, (2.5 ± 0.3) × 109 L mol–1 s–1, and (4.8 ± 0.2) × 108 L mol–1 s–1; with •OH – (6.3 ± 0.1) × 109 L mol–1 s–1, (6.7 ± 0.3) × 109 L mol–1 s–1, and (4.8 ± 0.3) × 109 L mol–1 s–1; and with NO3• – (1.5 ± 0.15) × 108 L mol–1 s–1, (8.4 ± 2.3) × 108 L mol–1 s–1, and (3.0 ± 0.7) × 107 L mol–1 s–1. The rate constants increased weakly with temperatures ranging from 278 to 318 K. The diffusional limitations of the rate constants appeared significant only for the GLV–•OH reactions. The aqueous-phase reactions appeared negligible in deliquescent aerosol and haze water but not in clouds and rains. The atmospheric lifetimes of GLVs decreased from many days to hours with increasing liquid water content and radicals' concentration.

The Atmosphere Special Issue “Atmospheric Aqueous-Phase Chemistry” comprises ten original articles dealing with different aspects of chemistry in atmospheric liquid water. [...]

At present, there are still numerous unresolved questions concerning the mechanisms of light-absorbing organic aerosol (brown carbon, BrC) formation in the atmosphere. Moreover, there is growing evidence that chemical processes in the atmospheric aqueous phase can be important. In this work, we investigate the aqueous-phase formation of BrC from 3-methylcatechol (3MC) under simulated sunlight conditions. The influence of different HNO2/NO2− concentrations on the kinetics of 3MC degradation and BrC formation was investigated. Under illumination, the degradation of 3MC is faster (k2nd(global) = 0.075 M−1·s−1) in comparison to its degradation in the dark under the same solution conditions (k2nd = 0.032 M−1·s−1). On the other hand, the yield of the main two products of the dark reaction (3-methyl-5-nitrocatechol, 3M5NC, and 3-methyl-4-nitrocatechol, 3M4NC) is low, suggesting different degradation pathways of 3MC in the sunlight. Besides the known primary reaction products with distinct absorption at 350 nm, second-generation products responsible for the absorption above 400 nm (e.g., hydroxy-3-methyl-5-nitrocatechol, 3M5NC-OH, and the oxidative cleavage products of 3M4NC) were also confirmed in the reaction mixture. The characteristic mass absorption coefficient (MAC) values were found to increase with the increase of NO2−/3MC concentration ratio (at the concentration ratio of 50, MAC is greater than 4 m2·g−1 at 350 nm) and decrease with the increasing wavelength, which is characteristic for BrC. Yet, in the dark, roughly 50% more BrC is produced at comparable solution conditions (in terms of MAC values). Our findings reveal that the aqueous-phase processing of 3MC in the presence of HNO2/NO2−, both under the sunlight and in the dark, may significantly contribute to secondary organic aerosol (SOA) light absorption.

Fine particulate matter (PM2.5) concentrations at the Middle Adriatic coastal site of Croatia were affected by different air-mass inflows and/or local sources and meteorological conditions, and peaked in summer. More polluted continental air-mass inflows mostly affected the area in the winter period, while southern marine pathways had higher impact in spring and summer. Chemical characterization of the water-soluble inorganic and organic ionic constituents is discussed with respect to seasonal trends, possible sources, and air-mass inputs. The largest contributors to the PM2.5 mass were sea salts modified by the presence of secondary sulfate-rich aerosols indicated also by principal component analysis. SO42− was the prevailing anion, while the anthropogenic SO42− (anth-nssSO42−) dominantly constituted the major non-sea-salt SO42− (nssSO42−) fraction. Being influenced by the marine origin, its biogenic fraction (bio-nssSO42−) increased particularly in the spring. During the investigated period, aerosols were generally acidic. High Cl− deficit was observed at Middle Adriatic location for which the acid displacement is primarily responsible. With nssSO42− being dominant in Cl− depletion, sulfur-containing species from anthropogenic pollution emissions may have profound impact on atmospheric composition through altering chlorine chemistry in this region. However, when accounting for the neutralization of H2SO4 by NH3, the potential of HNO3 and organic acids to considerably influence Cl− depletion is shown to increase. Intensive open-fire events substantially increased the PM2.5 concentrations and changed the water-soluble ion composition and aerosol acidity in summer of 2015. To our knowledge, this work presents the first time-resolved data evaluating the seasonal composition of water-soluble ions and their possible sources in PM2.5 at the Middle Adriatic area. This study contributes towards a better understanding of atmospheric composition in the coastal Adriatic area and serves as a basis for the comparison with future studies related to the air quality at the coastal Adriatic and/or Mediterranean regions.

The ultimate goal in the understanding of complex chemical processes is a complete description of the underlying reaction mechanism. In the present study and for this purpose, a novel experimental platform is introduced that builds upon electrochemistry capable of generating reactive intermediate species at the electrode surface. The atmospherically relevant nitration of catechols is taken as a case example. First, we confirm the recently proposed nitration mechanism, advancing the understanding of atmospheric brown carbon formation in the dark. We are able to selectively quantify aromatic isomers, which is beyond the limits of conventional electroanalysis. Second, we identify a new pathway of nitrocatechol hydroxylation, which proceeds simply by oxidation and the addition of water. This pathway can be environmentally significant in the dark aqueous-phase formation of secondary organic aerosols. Third, the developed methodology is capable of selectively detecting a wide range of nitroaromatics; a possible application in environmental monitoring is proposed.

Many ambiguities surround the possible mechanisms of colored and toxic nitrophenols formation in natural systems. Nitration of a biologically and environmentally relevant aromatic compound, guaiacol (2-methoxyphenol), under mild aqueous-phase conditions (ambient temperatures, pH 4.5) was investigated by a temperature-dependent experimental modeling coupled to extensive ab initio calculations to obtain the activation energies of the modeled reaction pathways. The importance of dark nonradical reactions is emphasized, involving nitrous (HNO2) and peroxynitrous (HOONO) acids. Oxidation by HOONO is shown to proceed via a nonradical pathway, possibly involving the nitronium ion (NO2+) formation. Using quantum chemical calculations at the MP2/6-31++g(d,p) level, NO2• is shown capable of abstracting a hydrogen atom from the phenolic group on the aromatic ring. In a protic solvent, the corresponding aryl radical can combine with HNO2 to yield OH• and, after a subsequent oxidation step, nitrated aromatic products. The demonstrated chemistry is especially important for understanding the aging of nighttime atmospheric deliquesced aerosol. The relevance should be further investigated in the atmospheric gaseous phase. The results of this study have direct implications for accurate modeling of the burden of toxic nitroaromatic pollutants, and the formation of atmospheric brown carbon and its associated influence on Earth's albedo and climate forcing.

Yellow-colored methylnitrocatechols (MNC) contribute to the total organic aerosol mass and significantly alter absorption properties of the atmosphere. To date, their formation mechanisms are still not understood. In this work, the intriguing role of HNO2 (catalytic and oxidative) in the dark transformation of 3-methylcatechol (3MC) under atmospherically relevant aqueous-phase conditions is emphasized. Three possible pathways of dark 3-methyl-5-nitrocatechol and 3-methyl-4-nitrocatechol formation, markedly dependent on reaction conditions, were considered. In the dominant pathway, HNO2 is directly involved in the transformation of 3MC via consecutive oxidation and conjugated addition reactions (nonradical reaction mechanism). The two-step nitration dominates at a pH around the p Ka of HNO2, which is typical for atmospheric aerosols, and is moderately dependent on temperature. Under very acidic conditions, the other two nitration pathways, oxidative aromatic nitration (electrophilic) and recombination of radical species, gain in importance. The predicted atmospheric lifetime of 3MC according to the dominant mechanism at these conditions (2.4 days at pH 4.5 and 25 °C) is more than 3-times shorter than that via the other two competitive pathways. Our results highlight the significance of a catechol oxidation-conjugated addition reaction in a nighttime secondary nitroaromatic chromophore formation in the atmosphere, especially in polluted environments with high NO x concentrations and relatively acidic particles (pH around 3).

Our current understanding of the importance of surface-active substances (SAS) on atmospheric aerosol cloud-forming efficiency is limited, as explicit data on the content of size-resolved ambient aerosol SAS, which are responsible for lowering the surface tension (σ) of activating droplets, are not available. We report on the first data comprising seasonal variability of size-segregated SAS concentrations in ambient aerosol particulate matter (PM). To assess the impact of SAS distribution within PM on cloud droplet activation and growth, a concept of surfactant activity was adopted and a parametrization developed; i.e., surfactant activity factor (SAF) was defined, which allowed translation of experimental data for use in cloud parcel modeling. The results show that SAS-induced σ depression during cloud activation may affect droplet number ( Nd) as much as a 2-fold increase in particle number, whereas by considering also the size distribution of particulate SAS, Nd may increase for another 10%. This study underscores the importance of size-resolved SAS perspective on cloud activation, as data typically obtained from aqueous extracts of PM2.5 and PM10 may result in misleading conclusions about droplet growth due to large mass fractions of supermicron particles with SAS deficit and little or no influence on CCN and Nd.

A widely used instrument for collecting size-segregated particles is the micro-orifice uniform deposit impactor (MOUDI). In this work, a 10-stage MOUDI (cut-point diameter of 10 µm to 56 nm) was used to collect samples in Ljubljana, Slovenia, and Martinska, Croatia. Filters, collected with and without rotation, were cut in half and analyzed for nine elements (As, Cu, Fe, Ni, Mn, Pb, Sb, V, Zn) using laser ablation ICP-MS. Elemental image maps (created with ImageJ) were converted to concentrations using NIST SRM 2783. Statistical analysis of the elemental maps indicated that for submicron particles (stages 6–10), ablating 10 % of the filter (0.5 cm2, 20 min ablation time) was sufficient to give values in good agreement (±10 %) to analysis of larger parts of the filter and with good precision (RSE < 1 %). Excellent sensitivity was also observed (e.g., 20 ± 0.2 pg m−3 V). The novel use of LA-ICP-MS, together with image mapping, provided a fast and sensitive method for elemental analysis of size-segregated MOUDI filters, particularly for submicron particles.

Long-term measurements of carbon in HUmic-LIke Substances (HULLS-C) of ambient size-segregated water soluble organic aerosols were performed using a ten-stage low-pressure Berner impactor from December 2014 to November 2015 at an urban background environment in Ljubljana, Slovenia. The mass size distribution patterns of measured species (PM - particulate matter, WSOC - water-soluble organic carbon and HULLS-C) for all seasons were generally tri-modal (primarily accumulation mode) but with significant seasonal variability. HULLS-C was found to have similar distributions as WSOC, with nearly the same mass median aerodynamic diameters (MMADs), except for winter when the HULLS-C size distribution was bimodal. In autumn and winter, the dominant accumulation mode with MMAD at ca. 0.65 mu m contributed 83 and 97% to the total HULLS-C concentration, respectively. HULIS-C accounted for a large fraction of WSOC, averaging more than 50% in autumn and 40% in winter. Alternatively, during warmer periods the contributions of ultrafine (27% in summer) and coarse mode (27% in spring) were also substantial. Based on mass size distribution characteristics, HULIS-C was found to be of various sources. In colder seasons, wood burning was confirmed as the most important HLTLIS source; secondary formation in atmospheric liquid water also contributed significantly, as revealed by the MMADs of the accumulation mode shifting to larger sizes. The distinct difference between the spring and summer ratios of HULIS-C/WSOC in fine particles (ca. 50% in spring, but only 10% in summer) indicated different sources and chemical composition of WSOC in summer (e.g., SOA formation from biogenic volatile organic compounds (BVOCs) via photochemistry). The enlarged amount of HULLS-C in the ultrafine mode in summer suggests that the important contribution was most likely from new particle formation during higher emissions of BVOC due to the vicinity of a mixed deciduous forest; the higher contribution of HULLS-C in the coarse mode demonstrated that beside soil erosion other sources, such as pollen and plant fragments, could also be responsible.

Properties, (trans)formation, and removal of organic particles remain the least understood aspects of atmospheric chemistry despite the importance of organic aerosol (OA) for both human health and climate change. Recently, organosulfur compounds (OS) have come into the focus of atmospheric research as significant reservoirs of S in the atmosphere, being potentially important components of gas-to- particle conversion and formation of secondary organic aerosol (SOA) especially in the oceanic region. Moreover, nitroaromatic compounds (NAC), as (methyl)nitrocatehols recently reported as potentially toxic constituents of aerosol water soluble organic matter (WSOM) and significant SOA tracers, have not been studied over marine atmosphere till now. A range of global exchange processes between the sea and the atmosphere is hindered by the sea surface microlayer (SML) generally enriched in surface active organics which form films and serve both as a sink and a source of marine OA. To better understand the role of surfactant films at the air-sea interface in global biogeochemistry as well as the sources and transport pathways of marine OA and to estimate their importance in global climate, it is necessary to study chemical composition and properties of trace organics, OS and NAC, in both the SML and marine aerosols as an integrated whole. We will present the first attempt to study marine aerosol WSOM as well as the SML collected in the Middle Adriatic with a special emphasis on its total S and OS content as well as on specific NAC. For that purpose a novel methodological approach capable of their quantification as well as determination of their surfactant nature is applied by combining liquid chromatography mass spectrometry, ion chromatography, inductively coupled plasma mass spectrometry, and electrochemistry. The obtained data are correlated with those for dissolved and particulate organic carbon, water soluble anions and cations, chlorophyll a, nutrients, and surfactants.

In recent studies, laser printers and photocopy machines have been identified as important sources of indoor air pollution with fine and ultrafine particles. In this work, the indoor pollution of a printing and photocopy center in Ljubljana, Slovenia was investigated. The particle number concentration time series and the particle size distributions were measured continuously for a period of one month by a scanning mobility particle sizer (SMPS). Our measurements clearly showed that during operating hours the total number concentration of nanoparticles (size between 15 and 750 nm) increased in both working rooms with laser printers as well as in a room with photocopy machines. In rooms with laser printers the bimodal particle size distribution was frequently observed (i.e. max. at ca. 20 or 30 nm and at ca. 100 nm), with the aged particles persisted in the room over the night and over the weekend. In the photocopy room the situation was different, again with a sharp increase in concentration of small particles (ca 20 nm) and their growth to bigger sizes, but after closing a decrease to the background concentration. The results undoubtedly proved that the fast increase in nanoparticles (size below 50 nm) was associated with processes, the intense laser printing and photocopying activity. Our study also confirmed that the ventilation of the room is a very important factor which affects the life time of aged nanoparticle in the indoor environment.