Concentrations of monoaromatic hydrocarbons in the air of the underground car park and individual garages attached to residential buildings

Science of the Total Environment 573 (2016) 767–777

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Concentrations of monoaromatic hydrocarbons in the air of the underground car park and individual garages attached to residential buildings Mariusz Marć a,⁎, Monika Śmiełowska a, Bożena Zabiegała a a

Department of Analytical Chemistry, Gdansk University of Technology, Gdansk, Poland

H I G H L I G H T S

G R A P H I C A L

A B S T R A C T

• Liquid fuel combustion is the main source of emission of BTEX into the two-level underground car park air; • The underground car park might be considered as the so-called "hot spot", a specific emission source of BTEX to urban air; • There was a meaningful relationship between the number of parked cars and the concentration of BTEX in the car park air; • The type of fuel for running the car considerably affects the concentration of BTEX in the residential garages air; • The garage used as a workshop and storage area had approx. 10-fold higher BTEX concentration in air than the other garages.

a r t i c l e

i n f o

Article history: Received 1 June 2016 Received in revised form 24 August 2016 Accepted 25 August 2016 Available online xxxx Editor: D. Barcelo Keywords: Underground car park BTEX Vehicle emissions Passive sampling Residential garages

a b s t r a c t The paper describes the characteristics of a two-level underground car park and three individual garages attached to residential buildings, differing by the resident utilization habits, located in North Poland (Tri-City agglomeration area). The strategy of collecting the analyte samples from air in mentioned enclosed areas, concerning the determination of benzene, toluene, ethylbenzene, o-xylene and p,m-xylenes (BTEX) concentrations was performed using passive sampling technique – Radiello® diffusive passive samplers with graphitised charcoal cartridge as a sorption medium. The stage of liberation and final determination of collected analytes was conducted with the use of thermal desorption-gas chromatography-flame ionisation detector (TD-GC-FID) system. As a result of the performed measurements in two-level underground car park, it was observed that the time-weighted average concentrations of BTEX in air were as follows: Level-1 – benzene – 5.2 ± 1.1 μg/m3, toluene – 12.3 ± 2.4 μg/m3, ethylbenzene 2.85 ± 0.80 μg/m3, o-xylene – 4.6 ± 1.4 μg/m3, p, m-xylenes – 8.8 ± 2,4 μg/m3; Level-2 – benzene - 5.2 ± 1.1 μg/m3, toluene – 12.9 ± 3.6 μg/m3, ethylbenzene – 2.73 ± 0.79 μg/ m3, o-xylene – 4.2 ± 1.1 μg/m3, p, m-xylenes – 8.5 ± 2.3 μg/m3. As for residential garages, the time-weighted average concentrations of BTEX in air were in the following ranges: from 5.9 to 53 μg/m3 (benzene), from 7.1 to 195 μg/m3 (toluene), from 3.0 to 39 μg/m3 (ethylbenzene), from 5.6 to 44 μg/m3 (o-xylene) and from 6.3 to 99 μg/m3 (p,m-xylenes). Also, BTEX concentration ratios such as: tol/benz ratio and (m, p)-xyl/et.benz coefficient,

⁎ Corresponding author at: Department of Analytical Chemistry, Gdansk University of Technology, Narutowicza Str. 11/12, PL 80-233 Gdansk, Poland. E-mail address: [email protected] (M. Marć).

http://dx.doi.org/10.1016/j.scitotenv.2016.08.173 0048-9697/© 2016 Elsevier B.V. All rights reserved.

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were calculated based on the obtained results to assess the “freshness” of air mass and the influence exerted by vehicle movement on the concentration of BTEX in air in studied enclosed areas. © 2016 Elsevier B.V. All rights reserved.

1. Introduction Garage enclosures and large-sized underground and aboveground car parks must be analysed as a specific type of microenvironment (Papakonstantinou et al., 2003). Such compartments are usually designed and built as an integral household element, or residential building (individual garages), or as separate, large-sized areas to store many cars in the same place, in a convenient fashion for employees of a company or enterprise, customers of large-sized stores, or residents of large housing estates (Demir, 2015). For freestanding car parks occupying large areas, it is very frequent to design and built them as underground compartments, instead of having them constructed in open area. Also, such a constructional solution requires process-related solutions to allow proper air circulation and air exchange inside the underground car park (Batterman et al., 2006a). The specificity of microenvironment in residential vehicle garages or underground car parks occupying large areas results from the fact that the air in this type of buildings contains chemical compounds that can occur at very high concentration levels. In addition, for garages attached to the households or residential buildings, pollutants may be transported from the garages to other rooms intended for occupants, e.g. kitchen, living room and bedroom (Batterman et al., 2006b, Dodson et al., 2008; Nirvan et al., 2012). Despite that the common user stays in such places for a relatively short time per day (access to the parking space, getting out of the car, approaching the exit of the underground car park), a very high accumulation of harmful compounds in the air is the reason for which the air in car parks can be classified as an additional element/factor of human exposure to xenobiotics, and consequently human health may be affected (Glorennec et al., 2008). Moreover, underground car parks can be recognized as the so-called “hot spots”, i.e. places posing a high impact on ambient air quality, significantly rising the concentrations of selected pollutants - organic compounds (mainly those in the group of VOCs), inorganic compounds (CO and NOx) and suspended particulate matter (PM10 and PM2.5) (Kim et al., 2007; Vuković et al., 2014). Therefore, for almost 15 years, many research centres have been making an attempt to obtain analytic information on the type, and the quantity of hazardous chemical compounds in the air in different types of large-sized car parks and various types of vehicle garages attached to the residential buildings or households. Fuel combustion is a main source of emissions - vehicle exhaust emissions are the dominant source of aromatic hydrocarbons which largely affects the quality of air in different types of car parks. Consequently, analysing the literature data on air quality in different types of car park areas, it can be noticed that the mostly following compounds or groups of chemical compounds have been determined: MTBE, benzene, toluene, ethylbenzene, xylenes (Hun et al., 2011), 1,3-butadiene, formaldehyde, CO, CO2, NOx, and total hydrocarbons (THCs) (Jo and Song 2001; Graham et al., 2004; Zielińska et al., 2012, Li and Xiang, 2013). Concentrations of chemical compounds determined in the air in car park areas depend on many factors, which can be generally classified as factors depending on: the characteristics of the motor vehicle, characteristics of the car park area (usable area, frequency of use, number of parked cars etc.) and meteorological conditions present in the open area. In case of large-sized car parks, one must pay attention to the fact that air circulation and air exchange inside the car park area is provided using a suitably designed ventilation system (Batterman et al., 2006a). Therefore, there is a risk that emitted pollutants can be transported by the ventilation system, directly into the ambient air.

Additionally, based on the information presented in the scientific literature, BTEX compounds (benzene, toluene, ethylbenzene, o-xylene, m, and p-xylenes) are referred to as indicators of the extent to which man is exposed to harmful chemicals from volatile organic compounds (VOCs) (Ly-Verdú et al., 2010). This paper presents research results to estimate concentrations of BTEX compounds in the air of a two-level underground car park in the close vicinity of a public utility building and used only by the employees of that institution. The study was conducted for 30 days, including week days (20 days) and weekends (10 days). Also, for comparison, the results of the research on the air quality (given as the concentration of BTEX compounds) in three individual garages attached to residential buildings are presented. The garages differed in cubature, their typical use (not only to park the vehicles) and the type of fuel used to drive the vehicle. The evaluation of indoor air quality in different types of garages (large-scale underground car park and individual garages) allows to assess the problem of BTEX emission to ambient air from sources that are not considered significant from the point of view of emission rates and their impact on the quality of the ambient air. This applies in particular to the individual garage spaces, where the air inside is not subject of regular monitoring or controlling systems, and which may be recognized as uncontrolled emission sources of BTEX compounds into the ambient air and deteriorating local ambient air quality. Also, in presented studies concerning a specific types of microenvironments (large-scale underground car park and individual garages), the BTEX concentration ratios such as: tol/benz ratio and (m, p)-xyl/ et.benz coefficient, were calculated based on the obtained results to assess the “freshness” of air mass and the vehicle movement intensity influence on the concentration of BTEX in air in studied enclosed areas. This is a specific approach in a case of mentioned microenvironment air quality research, due to the fact that BTEX concentration ratios are commonly applied in the field of urban air quality research. Radiello® diffusive passive samplers were used to collect samples of BTEX compounds from the gaseous phase. The application of passive sampling technique (in this type of research an alternative and more convenient solution than application of dynamic/active sampling devices) made it possible to conduct air quality measurements, both in the large-scale underground car park and individual garages without any interference with its normal functioning and use. 2. Materials and methods 2.1. Description of the BTEX sampling area The two-level underground park, upon which the air quality was studied for the concentration of BTEX compounds, is located in the city centre of Gdansk, Poland. This car park is not publically accessible as it is intended only for cars owned by employees of the public utility institution. The car park has two levels: Level 1 has 38 parking spaces (total parking area of 1571 m2; Level 2 has 45 parking spaces (total parking area of 1638 m2). There is only one entrance for the cars to access the underground car park (both to Level 1 and Level 2). In order to access level 2, one must travel along the access route is arranged within the entire area of Level 1. A detailed plan of the two-level underground car park in which the air quality was studied is presented in Fig. 1. Both car park levels are equipped with mechanical ventilation, which is activated periodically. The average temperature in the area on Level 1 and Level 2 was 13 ± 1 °C and 14 ± 2 °C, respectively.

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For individual garages attached to residential buildings, the study was performed in three garages, which significantly differed in their cubature and typical use. All three garages were located within the Tri-City agglomeration area (Gdansk, Gdynia and Sopot area). There was only one vehicle in each of the studied individual garages. During the study, the temperature inside the individual garage was monitored daily. The characteristics of individual garages attached to residential buildings are summarised in Table 1. 2.2. Analytical procedure – sample collection, liberation and final determination of analytes 2.2.1. Large-sized underground car park The analytes sampling (BTEX) from the gaseous phase were conducted using passive sampling devices - Radiello®, diffusive type (Fondazione Salvatore Maugeri, Padova, Italy), where the Carbograph 4 (graphitised charcoal, 300 ± 10 mg, 35–50 mesh) was used as a sorption bed. There were 6 measuring points on each levels of the underground car park. Locations of the sampling points were selected to minimise the influence of air movement occurring during operation of the underground car park ventilation system, the operation of which is based on a programmed activation sequence. Apart from the programmed ventilation and purging system in the underground car park area, there are also GAZEX® sensors that switch on the ventilation

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system if too high concentration of carbon monoxide or LPG is detected in the air. The passive sampling devices were installed at a height of 2 m along the main driving route for cars. A layout plan of both levels of the underground car park levels, with marked measuring points and the main route travelled by cars within the car park area are shown in Fig. 1. The measurements of the underground car park air quality were performed in winter at the turn of January and February 2016. The monitoring was done on weekdays and weekends. During the study the temperature on both levels of the underground car park was monitored as well. Each time, changing the cylindrical container filled with sorption bed placed in Radiello® passive sampler, the number of cars parked on the same level was routinely checked and documented. After completed exposure (24 h) the Radiello® cylindrical containers with the sorption bed were placed in glass vessels, sealed with a cap and transported to the laboratory. Prior to the final determination procedures, tubes filled with sorption beds were held at a temperature of approx. 5 °C for no longer than 24 h. The final stage of the analytical procedure, which involved liberation, gas chromatography (GC) separation and quantitate analysis of the BTEX compounds collected on the sorption bed, was performed by the two-staged thermal desorption system combined with gas chromatography using a flame ionisation detector (TD-GC-FID system). Detailed information on the applied analytical procedure is presented in Fig. 2.

Fig. 1. A layout view of the two-level underground car park: A) Level 1, B) Level 2.

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Table 1 General information about the research subjects – individual vehicle garages attached to residential buildings. Garage Internal diameters

Average temperature during the sampling period

Vehicle characteristics

Occupancy type of the garage

Garage 5.6 m × 3.5 no. 1 m × 2.1 m

10.5 ± 1.5 °C

• vehicle classification – car segment C (small family car), • fuel type – gasoline • car's age – 4 years • average presence time of the car per day in garage – 22 h

Garage 6.5 m × 3.0 no. 2 m × 2.0 m

11.5 ± 1.5 °C

Garage 5.5 m × 4.5 no. 3 m × 2.4 m

11.0 ± 1.0 °C

• vehicle classification – car segment C (small family car), • fuel type – diesel • car's age – 8 years • average presence time of the car per day in garage – 12 h • vehicle classification – car segment C (large family car), • fuel type – diesel • car's age – 2 years • average presence time of the car per day in garage – 14 h

• age of garage – 30 years, • place for parking one vehicle, • area used for various household repairs and renovation work (the so-call household workshop), • place used to store all types of vehicle fluids (windscreen washer, brake fluid, coolant), • compartment used to store various types of organic solvents (e.g. extraction naphtha), engine oil used in the vehicle, agents for car interior and body maintenance, open cans with paints, enamels and varnishes, various types of greases and synthetic oils as well as pesticides. • age of garage – 10 years, • place used only to store the motor vehicle, not used for other purposes, • storage of vehicle liquids (windscreen washer, brake fluid, coolant), • lack of containers with solvents, paints, varnishes, engine oils and lubricants.

• • • • •

2.2.2. Individual garages associated with accommodations spaces As for measurements in individual garages attached to residential buildings, 3 Radiello® diffusive passive sampling devices were installed each time in different points in the studied pleases at a height of approx. 2 m. The exposure time of the passive sampling devices in individual garages was shorter than the exposure time of sampling devices in the underground car park (24 h) and lasted for 12 h. Shorter exposure time was justified by the fact that concentration of BTEX compounds in the air in individual garages can be much higher than in the underground car park, due to much smaller cubature and a lower air circulation in individual garages (air exchange is mainly by opening and closing the entrance door). The measurement of air quality in individual garages was carried out for 7 days, including monitoring of the air temperature inside the garage. The analytical procedure – aimed at obtaining reliable analytical information on the level of BTEX compounds– was the same as in the study performed in the two-level underground car park. The concentration (C) of the analyte in the air samples was determined using the formula proposed by Radiello® diffusive passive sampler manufacturer and described in literature data by Fondelli et al., 2008 and Dumanoglu et al., 2014 (1): C air ¼

m Q 298 


T 1:5 298

t

 106

ð1Þ

where: m - amount of the analyte retained on a sorption bed [μg]; t - exposure time of passive sampler [min]; Cair - time-weighted average (TWA) concentration of the analyte determined in air [μg/m3]; Q298 – the analyte sampling rate at a temperature of 298 K and a pressure of 1013 hPa [ml/min]determined and defined by the manufacturer of the Radiello® passive sampling device; and T – average temperature during sampling [K]. The applied analytical procedure offers the possibility of liberating analytes from the sorption bed without the need to use organic solvents that are burdensome to the environment, which is consistent with the philosophy of “green analytic chemistry”.

age of garage – 5 years, place for parking one vehicle, area used for permanent storage of cut firewood, storage of vehicle liquids (windscreen washer, brake fluid, coolant) lack of containers with solvents, paints, varnishes, engine oils and lubricants.

compounds from the group of organic volatile compounds VOCs was used, including BTEX compounds, each with a concentration of 2000 μg/ml (EPA VOC Mix 2, Supelco, USA). Two five-point calibration curves were carried out with ranges: from 50 to 400 ng per tube filled with sorption bed, and from 400 to 2000 ng per tube filled with sorption bed. The correlation coefficient R2 of the calibration curves were in the range of 0.994 to 0.999 for all BTEX compounds. The method could not separate m-xylene and p-xylene; therefore these two compounds were quantified together. Detailed information on the Radiello® diffusive passive samplers, laboratory equipment and the analytical procedure used for calibration of the TDGC-FID system can be found in previous research papers (Zabiegała et al., 2011; Marć et al., 2014a, 2014b). 2.4. QA/QC of BTEX measurements Quality assurance of BTEX measurements in the air in the two-level underground car park and individual garages attached to residential buildings involved a determination of the blank value. For that purpose, a Radiello® cylindrical container filled with clean sorption bed that had not been exposed was analysed applying the same analytical procedure. All obtained results were corrected, taking into account the blank value (Król et al., 2012). In addition, the effectiveness of analyte desorption/ liberation from applied sorption bed (Carbograph 4) was investigated. Estimated values of recovery of analytes (BTEX compounds) from the sorption bed ranged from 98 to 103%. On the basis of obtained calibration curves characteristics (equations) the method quantification limit (MQL) of applied analytical procedure were estimated and ranged from 0.022 μg/m3 (for p, m-xylene) to 0.053 μg/m3 (for benzene). The values of the uncertainty (2σ) of the Q parameter (uptake rate of applied sampler) were evaluated by the manufacturer of the Radiello® diffusive passive sampling devices and ranged from 7.5% for benzene to 11.3 for p-xylene. 3. Results and discussion

2.3. Chemical standards and calibration of the TD-GC-FID system

3.1. Time weighted average concentration of BTEX compounds measured in the air in the two-level underground car park area

For quantitative analysis of BTEX compounds the external-standard (ESTD) method was applied. For that purpose, a mix of 13 chemical

According to guidelines published in European legislation (Directive 2008/50/EC), the annual average of benzene concentration determined

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Fig. 2. A diagram of the analytical procedure used for the determination of BTEX compounds in the two-level underground car park air.

in the ambient air in an urban area cannot exceed 5 μg/m3. According to experts from the International Agency for Research on Cancer, benzene was classified among Group I as a compound with documented carcinogenic properties (I.A.R.C, 1982). According to research results published in research papers, long-lasting exposure to benzene may result in an increased incidence of aplastic anaemia and acute myeloid leukaemia (Pariselli et al., 2009; Schiavon et al., 2015). Garage and parking facilities are specific types of buildings: their air quality is frequently without continuous (routine) monitoring or it is monitored randomly or occasionally. It is alarming that the

concentration of xenobiotics in the air in large-sized underground car parks and individual garages attached to residential buildings can be much higher than in the ambient air (Shinohara et al., 2009). Table 2 summarises the results of the study of the air quality assessment for the two-level underground car park, a 30-day TWA concentration of BTEX compounds as well as minimum and maximal concentrations obtained are presented. Detailed information on the variability of the daily (time-weighted) concentration of BTEX compounds, determined in the air in the underground car park, is presented in Supplementary Materials (Supplementary Figs. 1, 2 and 3). While

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interpreting the data in Table 2, it is noticeable that time-weighted average concentration of benzene determined in the air in the underground car park during regular use (on work days), both on Level 1 and Level 2, exceeded 5 μg/m3 (6.1 ± 1.4 μg/m3 and 6.0 ± 1.7 μg/m3, respectively). As far as the studies conducted on weekends are concerned, it was found that the concentration of benzene in the air in the underground car park, both on Level 1 and Level 2, was slightly lower and equal to 4.37 ± 0.82 μg/m3 and 4.36 ± 0.57 μg/m3, respectively. Differences between the concentration of BTEX compounds determined in the air in the underground car park on weekdays, and on weekends, are caused by a small number (b10) of cars left at the car park during weekends. Nevertheless, it can be noted that the TWA concentration of benzene is at a rather high level, despite the small number of cars on both levels of the car park. It can result from a reduced frequency of ventilation in the underground car park on weekends (reduced activity of the main sensor – number of cars), affecting the frequency of switching on the ventilation system. The limitation of air exchange creates favourable conditions for an elevated concentration of organic compounds in the air in the underground car park. On the other hand, occurrence of the mentioned phenomenon at weekends may force one to conclude that organic compounds emitted by using motor vehicles in the underground car park may be adsorbed on wall surfaces, supporting columns and other elements of the underground car park and then liberated into the air in the underground car park. While comparing concentrations of individual BTEX compounds determined in the air in the underground car park on regular working days on Level 1 with concentrations on Level 2, it can be noted that there are no significant differences between the concentrations determined on selected car park levels. This was also observed for results obtained on weekends. It is worth noting that the concentration of ethylbenzene and xylenes in the air in the underground car park on weekends was slightly higher on Level 1 than Level 2, i.e. 10.4% and 14.2%, respectively. An occurrence of this type of phenomenon, both on weekdays (intensive use of the underground car park) and on weekends (occasional use of the parking space), may result from two main factors: (i) number of motor vehicles passing through the parking area on Level 1 – users Table 2 The time-weighted average concentrations of BTEX compounds determined in the twostage underground parking air during 30 days sampling period. Working days (n = 20)

Benzene [μg/m3]

Toluene [μg/m3]

Ethylbenzene [μg/m3]

o-Xylene [μg/m3]

p, m-Xylene [μg/m3]

Level-1 Average Standard dev. Median Min Max

6.1 1.4 6,0 3.0 13.1

15.8 3.2 15.5 8.6 28.7

3.4 1.0 3.2 1.5 6.3

5.7 1.6 5.5 2.8 15.1

10.9 3.3 10.4 5.6 24.9

Level-2 Average Standard dev. Median Min Max

6.0 1.7 5.8 2.0 13.6

16.7 5.3 15.1 7.7 34.9

3.4 1.1 3.1 0.9 8.0

5.5 1.6 5.1 2.8 12.5

10.7 3.4 10.0 3.9 24.2

Benzene [μg/m3]

Toluene [μg/m3]

Ethylbenzene [μg/m3]

o-Xylene [μg/m3]

p, m-Xylene [μg/m3]

4.4 0.8 4.2 1.7 7.8

8.8 1.6 8.7 4.6 14.5

2.3 0.6 2.3 1.4 3.8

3.6 1.1 3.3 1.8 10.1

6.8 1.6 6.6 4.0 11.6

4.4 0.6 4.3 1.7 9.7

9.1 1.8 8.7 3.9 16.0

2.1 0.4 2.1 1.2 3.5

2.9 0.7 2.9 1.0 4.6

6.2 1.3 6.2 3.6 10.3

Weekends (n = 10) Level-1 Average Standard dev. Median Min Max Level-2 Average Standard dev. Median Min Max

who own parking spaces on Level 2 (they must drive through the entire car park on Level 1 to access Level 2); (ii) the location of the exit of the underground car park on Level 1 (exit of the entire underground car park is located very close to the car park on Level 1). In view of the fact that the car park exit is arranged at an angle, all drivers of motor vehicles must appropriately increase engine output for the departure of the underground car park (instantaneous increase in emission of liquid fuel combustion products into the air in the underground car park). Despite the presence of the factors affecting the content of BTEX compounds in the air in the underground car park on Level 1, the TWA concentration of BTEX compounds determined in the air on Level 1 and Level 2 during the study did not differ statistically significant; the biggest difference between the determined concentration in the air on selected car park levels amounted to 14.2%. This phenomenon may be influenced by such factors associated with two-level underground car park characteristics as: (i) close location of the exit/entrance from/to the underground car park on Level 1, which may dilute pollutants present in the air in the underground car park by the ambient air and transport of organic compounds from the air in the underground car park (mainly from Level 1) into the ambient air; (ii) a smaller number of vehicles parked by users on Level 1 during the measurement, compared to Level 2 (there were 19 vehicles on average on Level 1, and 21 vehicles on Level 2) ; (iii) occurrence of additional forced air circulation on Level 1. This circulation is caused by moving vehicles that pass through the area on level − 1 to access the car park area on Level 2. In addition, the difference between the concentration of BTEX compounds determined in the air on the two levels of the underground car park may result from the type of fuel driving the vehicles (gasoline, diesel fuel or LPG) and age of the vehicles parked on each level; for older vehicles, it is possible that the process of fuel combustion in the engine is not optimally effective, and it is very likely that the car park surface is contaminated with liquids leaking from vehicles, e.g. engine oil. Apart from determination of the concentration of BTEX compounds in the air on each level of the underground car park, it was attempted to estimate the relationship between the number of cars parked and the total content of BTEX compounds in the air inside the underground car park. Fig. 3 shows the relationship (expressed by means of the coefficient of determination R2) between the number of cars parked by users of the underground car park on individual levels and the total concentration of BTEX compounds determined in the air. While interpreting the information resented in Fig. 3, it can be claimed that there is a meaningful relationship (R2(level-1) = 0.68 and R2(level-2) = 0.55) between the number of parked cars on the defined level and the concentration of BTEX compounds determined in the air on the level. The coefficient of the determination calculated for Level 1 indicates that the number of parked cars on the level has a more significant influence on the amount of BTEX compounds, compared to Level 2. Additionally, a higher value of the R2 coefficient results from the fact that people owning parking places on Level 2 must travel through the entire area of the car park on Level 1. In order to illustrate the scale of the problem with air quality in large-sized underground car parks, the obtained results were compared with the average concentration of BTEX compounds determined in the ambient air. The concentrations of BTEX compounds in ambient air were obtained from the Foundation Agency of Regional Air Quality Monitoring in the Gdansk ARMAAG, which is the institution that provided the results of ambient air quality measurements. According to the data made available, the average concentration of benzene, toluene and xylenes in the ambient air within the study period (30 days) were as follow: 1.6 ± 1.1 μg/m3; 1.28 ± 0.98 μg/m3 and 2.6 ± 2.8 μg/m3. While comparing the information with the data summarised in Table 2, it can be noted that the average concentration of benzene, toluene and xylenes determined in the air in the underground car park is higher than in the ambient air. For example, the concentration of benzene determined in the air in the underground car park during daily use (working days) is N3.5-fold higher than the concentration of benzene

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Fig. 3. Relationship between the amount of vehicles parked by employees in the two-level underground car park and the total BTEX compounds measured in the air in the monitoring place.

determined in the ambient air. A higher concentration of benzene and other organic compounds determined in the air also results from the fact that the underground car park is the place where the vehicle engine is started up, and hence the engine fails to attaint optimum operating parameters at the beginning. Driving within the underground car park

with the “cold engine” (disadvantageous conditions for combustion of liquid fuel in the engine) gives rise to emissions of organic compounds into the air. Studies have highlighted the problem that the large underground car parks can be a source of emissions of BTEX compounds into the

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ambient air. This is possible when the underground car park ventilation system is not equipped with an adequate air cleaning system for the air transported from inside the underground car park into the ambient air. 3.2. BTEX concentration ratios determined in the air in the two-level underground car park area According to the data presented in the literature, in the case when the movement/operation of vehicles with combustion engines is the main (sometimes, the only) source of emissions: the toluene to benzene concentration ratio range from 1.3 to 4.3. The lower the value of the toluene/benzene ratio, one can claim with a higher probability how significant the influence exerted by vehicle movement on the concentration of BTEX compounds in air is. However, the defined values of the tol/ benz ratio relate to air quality measurements in urbanised areas, according to Miller et al., 2010, Yurdakul et al. (2013) as well as Rad et al. (2014), mainly along main communication paths or routes passing through a tunnel. For the BTEX ratios (illustrating the concentration ration of individual BTEX compounds relative to the determined concentration of ethylbenzene), the values reported in the literature, defining the main effect of traffic on ambient air quality, amount to 3:4:1:5, as determined by Chiang et al. (1996) and Khoder (2007). Table 3 summarises the data on the determined values of the BTEX inter-species concentration ratio, which makes it possible to define the main source of emissions of BTEX compounds into air, or specify how significant the effect of vehicle movement on air quality in the monitored enclosed area is. The data were divided into the period of the measurement performed on week/working days and weekends. While interpreting the data listed in Table 3, both for the measurement performed on weekdays (regular use of the underground car park) and on weekends, one can note that the determined tol/benz ratios were always higher for the studied air on Level 2, compared to the air on Level 1, and amounted to 10.2% and 8.6%, respectively. The main cause of the situation is the aforementioned vehicle movement: the owners of which have parking spaces located on Level 2; they must drive through the entire car park on Level 1 to access their parking spaces. While Table 3 The average BTEX inter-species concentration ratios in underground two-stage car park area. BTEX concentration ratios at Level-1 in underground car park during working days Parameter Average Range Average Range

Tol/benz 2.65 1.62 ÷ 3.75 B: 1.83 1.32 ÷ 2.81

p, m-xyl/benz 1.84 1.13 ÷ 2.45 T: 4.70 3.54 ÷ 6.22

o-xyl/benz 0.95 0.69 ÷ 1.23 E: 1.00 1.00

p, m-xyl/ethbenz 3.24 2.94 ÷ 3.60 X 4.93 4.48 ÷ 5.30

BTEX concentration ratios at Level-2 in underground car park during working days Parameter Tol/benz p, m-Xyl/benz o-Xyl/benz p, m-Xyl/ethbenz Average 2.92 1.89 0.96 3.25 Range 1.61 ÷ 3.89 0.99 ÷ 3.01 0.54 ÷ 1.50 2.66 ÷ 3.56 B: T: E: X Average 1.85 5.08 1.00 4.93 Range 1.04 ÷ 3.40 3.91 ÷ 6.37 1.00 3.86 ÷ 5.55 BTEX concentration ratios at Level-1 in underground car park during weekends Parameter Tol/benz p, m-xyl/benz o-xyl/benz p, m-xyl/ethbenz Average 2.10 1.71 0.89 2.90 Range 1.81 ÷ 2.71 1.13 ÷ 2.64 0.54 ÷ 1.23 2.72 ÷ 3.11 B: T: E: X Average 1.83 3.72 1.00 4.43 Range 1.11 ÷ 2.40 3.02 ÷ 4.46 1.00 4.00 ÷ 4.79 BTEX concentration ratios at Level-2 in underground car park during weekends Parameter Tol/benz p, m-Xyl/benz o-Xyl/benz p, m-Xyl/ethbenz Average 2.28 1.62 0.75 2.95 Range 1.63 ÷ 2.84 1.01 ÷ 2.48 0.46 ÷ 1.00 2.82 ÷ 3.05 B: T: E: X Average 1.97 4.27 1.00 4.33 Range 1.21 ÷ 2.78 3.43 ÷ 4.53 1.00 4.09 ÷ 4.60

comparing the determined the tol/benz ratio with the value reported in the literature (from 1.3 to 4.3), it is noticeable that the values were within the range described in the literature in all cases. This indicates that both on weekdays, when the underground car park area is regularly used, and on weekends, when use of the underground car park is occasional: the activity of vehicles with combustion engines is the main emission source. Slight differences between tol/benz ratios determined for individual levels can also result from the characteristics of vehicles (their age, technical condition, type and quality of fuel) and various style of driving a vehicle. For the p/m-xyl/ethbenz ratio (used to determine to so-called “freshness” of air mass), the determined values for Level 1 and Level 2 during regular use of the underground car park on work days were very similar to one another (3.24 and 3.25, respectively), and similar to the value reported in the literature (3.3 or higher), too. The occurrence of this relationship indicates that BTEX compounds are emitted into the air in the underground car park by “fresh” and intensive emission sources, here the vehicle movement. This makes it possible to conclude that chemical compounds emitted into the air in the underground car park are removed by the ventilation system, directly into the ambient air surrounding the monitored, large-sized underground car park. This fact may be in turn proof that large-sized underground car parks can be classified as the so-called “hot spots”, i.e. significant and specific emission sources of chemical compounds into the ambient air in urbanised areas. Smaller values of the tol/benz ratio (by 11.7% and 10.2%, respectively), determined during occasional use of the underground car park on weekends, are caused by an decrease in the number of cars parked within the entire underground car park at that time (reduced activity of the main emission source). In addition, smaller values of the p/m-xyl/ ethbenz ratio determined during occasional use may result from the occurrence of dilution of pollutants in the air in the underground car park due to a too small number of emission sources (vehicles) and cyclicallyoperated ventilation (independently of the number of vehicles). Referring to the information summarised in Table 3 with regard to the BTEX inter-species concentration ratio, it can be noted that the determined values of that parameter for the air in the car park on Level 1 and Level 2 during regular use were very similar to one another. Therefore, it can be concluded that air quality in the underground car park on the specified car park levels is only affected by vehicle movement. Small differences between the determined BTEX concentration ratios and the data in the literature (3:4:1:5) may result from the type and quality of fuel used, age and efficiency of the car, the driving styles well as in the intensity and efficiency of the installed ventilation system. Moreover, the results described in the literature with regard to the determination of BTEX concentration ratios refer not to measurements carried out in places, such as the underground car park, but studies performed along a communication route (increased vehicle traffic, open space). Considerably lower values of BTEX concentration ratios, determined for the air in the underground car park to rig occasional use on the weekend, results from the fact that vehicle traffic is very limited during this time. Additionally, the intensity of the emission of BTEX compounds into the air in the underground car park on weekends is very low; consequently, the values of BTEX concentration ratios are affected. 3.3. BTEX concentration in the indoor air in vehicle garages attached to households Another, very different in particular due to the number of parked cars and ventilation extent, example of places intended for parking motor vehicles includes individual garages attached to residential buildings. According to the data published in the scientific literature vehicles driven engines, in which the fuel is diesel oil, are less intense source of emissions of various types of hydrocarbons (HC) and carbon monoxide, than vehicles powered by engines, in which gasoline is used as fuel. While the vehicles powered by diesel fuel are more intense emission source of nitrogen oxides (NOx) and particulate matter (PM) into air

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(Giechaskiel et al., 2014; Reşitoğlu et al., 2015). Because of this, there is a good chance that in the individual garage areas, in which the left are vehicles with gasoline engines, the concentration of organic compounds in the air (particular, the BTEX compounds) can be much greater compared to individual garages where diesel vehicles are parked. Table 4 summarises the information on the time-weighted average concentration of BTEX compounds determined in the air in three types of garages attached to residential buildings. Referring to the data presented in Table 4, it can be noted that the concentration of BTEX compounds in the air in garage no. 1 was much higher than in the other two garages. By analysing the total average content of BTEX compounds (ΣBTEX) in the air in the studied garages, it was observed that ΣBTEX concentration for Garage no. 1 was equal to 431 ± 171 μg/m3, whereas in Garages no. 2 was 29 ± 11 μg/m3 (almost 15-fold less) and in garages no. 3, was 49 ± 11 μg/m3 (N8.5-fold less). A much higher concentration of BTEX compounds determined in the air in the garage no. 1 is caused by the following factors: (i) a very long time for parking the car in the garage (approximately 22 h per day on average), which consequently results in very low air circulation inside the garage (very low frequency of opening the entrance door to the garage and no forced ventilation between the air in the garage and the ambient air); (ii) type of fuel consumed by the motor vehicle (the studied garage no. 1 was used to park a gasoline engine car which, according to the earlier information, may considerably affect the increase in the concentration of organic compounds (BTEX compounds as well) in the air; (iii) evaporative emission of BTEX compounds from parked motor vehicle – according to the results published by de Castro et al. (2015), evaporation process of BTEX compounds from parked cars might be considered as one of the main factors, which influences significantly (increases) the concentration of monoaromatic hydrocarbons (mainly BTEX compounds) in garage air (including both evaporation from motor vehicle and evaporation from potential spills of gasoline or engine oil); (iv) the garage being used as a workshop for different repairs and maintenance. Therefore, the garage is used to store different types of containers with adhesives, paints, enamels, varnishes, organic solvents and car interior and body cleaning agents, which create an intensive source of emission of organic compounds into the studied environment in the garage no. 1. Consequently, all the mentioned factors considerably induce very high content levels of BTEX compounds in the air in Garage no. 1 Additionally, the time-weighted average of benzene was almost 10-fold higher (53 ± 22 μg/m3), than in the other garages - no. 2 and no. 3 (6.9 ± 2.2 μg/m3 and 5.9 ± 1.6 μg/m3, respectively). Such a high Table 4 The time-weighted average concentrations of BTEX compounds determined in the air in three different vehicle garages attached to residential buildings. Working days (n = 7)

Benzene [μg/m3]

Toluene [μg/m3]

Ethylbenzene [μg/m3]

o-Xylene [μg/m3]

p, m-Xylene [μg/m3]

Residential vehicle garage no. 1 - fuel used in motor vehicle - gasoline Average 53 195 39 44 99 Standard dev. 22 98 13 10 28 Median 59 168 41 45 106 Min 19 71 19 26 52 Max 89 366 59 64 143 Residential vehicle garage no. 2 - fuel used in motor vehicle - diesel Average 6.9 7.1 2.96 5.6 Standard dev. 2.2 3.3 0.83 2.3 Median 6.7 5.8 2.95 5.3 Min 2.2 3.8 1.84 1.9 Max 12.0 14.0 5.23 11.4

6.3 2.8 5.6 2.4 12.2

Residential vehicle garage no. 3 - fuel used in motor vehicle - diesel Average 5.9 10.7 6.6 9.5 Standard dev. 1.6 2.0 1.2 3.9 Median 5.6 11.0 6.6 8.2 Min 3.7 7.4 5.0 3.1 Max 8.7 14.9 9.7 16.6

16.5 2.2 16.5 12.7 19.8

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benzene concentration in the air in Garage no. 1 may pose very serious health hazards to users staying in this place, even if the frequency of being present there is relatively low. Also, it was noted that the concentration of benzene, toluene, ethylbenzene and total xylenes in the air in individual garage no. 1 was approximately 9-fold, 12-fold and approximately 9-fold and 7-fold lower, respectively, compared to the concentration of such compounds determined in the air in the two-level underground car park. This is particularly a consequence of forced air circulation inside the two-level underground car park due to the installed ventilation system. For garages no. 2 and no. 3, it can be noted that the results obtained of the studies associated with the content level of BTEX compounds in air are similar. It may result from the fact that the users own similar types of motor vehicles and that same type of engine (diesel). Additionally, garages no. 2 and no. 3 are used for practical purposes on a daily basis as storage for the car and its related accessories. A slightly higher concentration of toluene and xylenes determined in the air in garage no. 3 may result that this place is used to store firewood, which may act as a natural sorbent and, depending on temperature conditions, adsorb organic compounds or liberate previously retained compounds into the garage air. Moreover, the presence of small fluctuations between the determined concentration of BTEX compounds in the air in garages no. 2 and no. 3 may result from the quality of the fuel oil used and the time for which the motor vehicle has been parked in the garage. For garage no. 2, the average time, in which the motor vehicle has been present was the shortest - approximately 12 h per day. Additional factors that might influence the concentration level of BTEX compounds in such enclosed places, like individual residential garages are i.e. applied heating source or system in the garage, cigarette smoking by vehicle users inside the car or inside garage, or the age of garage. In a case of described individual residential garages, there was a lack of any heating systems (central heating systems or individual furnaces). Therefore, the impact of this factor might be omitted. Similarly, in a case of the impact of tobacco smoke on air quality in enclosed areas, in none of the described individual garages their users were active tobacco smokers. For this reason, the influence of this factor on the fluctuations between the BTEX concentrations measured in garages air also might be omitted. In order to estimate the extent to which the activity of motor vehicles parked in garages effects air quality in that place, BTEX inter-species concentration ratios (see Table 5) were determined, based on the obtained measurement results. Taking into account information summarised in Table 5, it is to be noted that the tol/benz ratio determined based on the obtained results for the air in garages no. 1 and no. 3 are within the range reported in the literature (from 1.3 to 4.3), which indicates a clear influence exerted by motor vehicle activity on the air quality in the studied places. A considerably higher value of the tol/benz ratio determined for the air in garage no. 1 indicates the presence of additional intensive sources of toluene into the air, such as varnishes, enamels, paints, organic solvents and engine oil. In addition, according to the already presented characteristics of garage no. 1 (see Table 1), the motor vehicle was present in the garage for the longest period of time (approximately 22 h per day on average). The smallest value of the tol/benz ratio was determined for the air in garage no. 2. This phenomenon may be associated with the fact that the motor vehicle was parked in the studied place for the shortest period of time (approximately 12 h per day on average). Additionally, this fact also indicates that there were no other sources of toluene emissions into the garage air, as the sources would considerably affect air quality. Comparing the obtained values of the p, m-xyl/ethbenz ratio confirmed that the time in which the motor vehicle is present in the garage, which is also associated with the frequency of use, and the fact that there is no ventilation in the garage exerts an appreciable effect on air quality. The highest values of the p, m-xyl/ethbenz ratio were recorded in garage no. 1, which indicates that BTEX compounds present in the

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Table 5 The average BTEX inter-species concentration ratios determined in three different vehicle garages attached to residential buildings. BTEX inter-species ratios at residential vehicle garage no. 1 - fuel used in motor vehicle - gasoline Parameter Average Range Average Range

Tol/benz 3.56 2.41 ÷ 4.41 B: 1.35 1.13 ÷ 1.57

p, m-Xyl/benz 1.95 1.58 ÷ 2.47 T: 4.80 3.88 ÷ 6.53

o-Xyl/benz 0.90 0.65 ÷ 1.24 E: 1.00 1.00

p, m-Xyl/ethbenz 2.60 2.35 ÷ 2.87 X 3.79 3.23 ÷ 4.20

BTEX inter-species ratios at residential vehicle garage no. 2 - fuel used in motor vehicle - diesel Parameter Tol/benz p, m-Xyl/benz o-Xyl/benz p, m-Xyl/ethbenz Average 1.05 0.94 0.84 2.09 Range 0.53 ÷ 2.02 0.58 ÷ 1.77 0.47 ÷ 1.50 1.61 ÷ 2.81 B: T: E: X Average 2.44 2.35 1.00 3.93 Range 1.47 ÷ 3.48 1.68 ÷ 3.59 1.00 3.13 ÷ 4.80 BTEX inter-species ratios at residential vehicle garage no. 2 - fuel used in motor vehicle - diesel Parameter tol/benz p, m-Xyl/benz o-Xyl/benz p, m-Xyl/ethbenz Average 1.82 2.86 1.68 2.52 Range 1.49 ÷ 2.20 2.03 ÷ 3.40 0.76 ÷ 2.58 2.13 ÷ 3.02 B: T: E: X Average 0.90 1.62 1.00 3.97 Range 0.68 ÷ 1.05 1.36 ÷ 1.85 1.00 3.21 ÷ 5.12

environment in this area originate from a relatively “fresh” emission source. Also, the highest value of the p, m-xyl/ethbenz ratio results from the fact that the motor vehicle in garage no. 1 was stored for the longest period of time and the extent of air exchange between the garage air and the ambient air is of the smallest value. This indicates that garage no. 1 can be classified as fixed local source of emission of BTEX compounds into the ambient air. The smallest value of the p, m-xyl/ ethbenz ratio was recorded for the air in garage no. 2, which results from the shortest time in which the motor vehicle was kept in the garage, the highest frequency (among all studied individual garages) of using the garage (frequency of opening and closing the garage door of the garage). At this point it should be mentioned that the differences between the obtained values of the parameter p, m-xyl/ethbenz ratio, and the value reported in the scientific literature (over 3.3) can be the result of the unavailability of factors initiating processes of air self-cleaning, as a result of the photochemical reactions. There is no light access (very often this type of building has no windows or, if present, such windows have very small dimensions), as a result, it is impossible the formation of hydroxyl radicals. This is a consequence of the insufficient frequency of ventilation in garages, which takes place only by opening and closing the main garage door. For comparison, the determined values of the p, m-xyl/ethbenz ratio for underground car park air are very similar to the values published in the scientific literature. The reason for this situation is given by the fact that air exchange in the two-level underground car park is regular as the car park is equipped with a ventilation system. 3.4. Comparison of indoor air quality in the two-level underground car park and individual garages attached to residential buildings Presented studies on indoor air quality in different type of garages showed that concentrations of BTEX compounds both in indoor twolevel underground car park, with forced ventilation system, as well as in small, individual garages attached to residential buildings are always higher than the allowable concentrations of these compounds in ambient air (see Table 2 and Table 4). The study of the air quality from different types of garages – largescale underground car park and individual garages attached to residential buildings allows for better documentation and confirmation of the

fact that garages are or can be emission sources of BTEX compounds to ambient air, regardless of the size and type of the garages. The research has also shown that the way of utilization of individual garages attached to residential buildings can drastically affect the air quality in these areas. Very high concentrations of BTEX compounds were observed when garages were used by their owners as storage rooms, for example for storage of various types of materials and household products. 4. Conclusions As a result of the study on air quality in the underground car park, it was concluded that the concentration of benzene is considerably higher, compared to the ambient air surrounding the underground car park. Liquid fuel combustion in engines of vehicles is the main source of emission of BTEX compounds into the air in the 2nd level underground car park. Also, it was found that an appreciable effect on air quality in the car park is exerted by the number of cars parked on the car park level and the close location of the exit/entrance to/from the car park as the amount of consumed fuel must be increased so that the car can ascend at the right speed. Despite very short human exposure to harmful compounds present in the air in the underground car park, it was proven that air quality in this type of place presents a major problem to be taken into account under future legal regulations related to air quality inhaled by humans during the entire day. Due to the fact, that in most cases large-scale car parks are located below ground level, it is necessary to provide regular air ventilation (appropriately programmed and efficient) inside the underground car park to provide the removal of pollutants outside the underground car park area (into the ambient air). If a suitable treatment system, which evacuates the air from inside the underground car park, is missing, this type of place can be classified as a distinct source of the emission of organic compounds into the ambient air, i.e. the so-called “hot spots”. Following the interpretation of the performed measurement to obtain analytical information on the air quality in garages attached to houses/residential buildings, it is concluded that there are major factors affecting the concentration of BTEX compounds in the air and are as follows: (i) type of fuel consumed by the vehicle; (ii) time of presence of the vehicle inside the garage; (iii) other intended uses of the garage, e.g. workshop for various repairs and maintenance or storage of paints, varnishes, organic reagents as well as vehicle oil and lubricants. High – sometimes even very high – concentrations of harmful organic compounds (mainly benzene) as recorded in the air in the studied garages can be a consequence of too little air circulation inside such places. Additionally, interpretation of the obtained results concludes that air quality in areas intended for vehicle parking can exert a very distinct effect on the health and comfort of those who use such places. Conflict of interest The authors declare that they have no conflict of interest. Acknowledgments The study has been funded by the Ministry of Science and Higher Education under the Iuventus Plus programme in the years 2015–2017, project no. IP2014 028373. The authors are grateful to the Agency of the Regional Air Quality Monitoring Foundation in the Gdansk Metropolitan Area (ARMAAG Foundation) and to Michalina Bielawska for providing meteorological and BTX concentration data. The authors would like to their express gratitude to the Security Department for the opportunity to conduct their research and to Sławomir Tkaczyk for his technical cooperation.

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