Seasonal variations and mass closure analysis of particulate matter in Hong Kong

The chemical characteristics of ambient particulate matters in urban and rural areas of Hong Kong were determined in this study. A monitoring program starting from November 2000 to February 2001 (winter) and June 2001 to August 2001 (summer) for PM10 and PM2.5 was performed at three monitoring stations in Hong Kong. Twenty-four-hour PM10 and PM2.5 samples were collected once every 6 days at two urban sites, PolyU and KT, and every 12 days at a background site, HT, with Hi-Vol samplers. High concentrations of OC, EC (except in PolyU), water-soluble ions and elements were observed in winter among the three sampling sites for PM10 and PM2.5 fractions. Seasonal variations were significant in background HT. Dilution effect due to the increase in mixing depth and precipitation in summer reduced the concentrations of particulate matters. Long-range transport could contribute to the higher concentrations of particulate matter in the winter. Chemical mass closure calculations were performed for PM10 and PM2.5 observed. Mass closure improved when separate factors (1.4 and 1.9 respectively) were used to convert water-soluble organic carbon (WSOC) and water-insoluble organic carbon (WINSOC) into corresponding organic masses. The urban sites showed high percentages of water-soluble ions in winter and high percentages of carbonaceous species in summer. Better results were obtained for the chemical mass closure analysis in winter than in summer. High temperature and solar radiation in summer increased the rate of the complex photochemical reaction in the atmosphere. Therefore the chemical mass closure analysis would underestimate the volatized species and secondary aerosols during summer.     

Commuter exposure to aromatic VOCs in public transportation modes in Hong Kong

This study investigated commuter exposure to aromatic volatile organic compounds (VOCs) in different commuting microenvironments. In Hong Kong, more than 90% of the local citizens rely on public transport facilities in their daily commutes. During five winter months in late 2001 and early 2002, in-vehicle monitoring was performed in nine popular public transportation modes: tram, public light bus, air-conditioned bus, non-air-conditioned bus, taxi, ferry and three railway systems (Mass Transit Railway-MTR, Kowloon-Canton Railway-KCR and Light Rail Transit-LRT). These transports were grouped into three categories: railway transport, roadway transport and marine transport. Air samples of benzene, toluene, ethylbenzene and m/p/o-xylene were collected by canisters and analysed by gas chromatography and mass selective detector technique. Results indicated that the in-vehicle VOC exposure levels were greatly influenced by the mode of transport. For benzene, mean concentration ranged from 4.8 to 6.1 microg x m(-3) in roadway transports, 3.0-3.8 microg x m(-3) in railway transports and it was 2.1 microg x m(-3) in ferry. Regardless of the results in MTR and air-conditioned buses, the VOC levels in roadway transport were the highest and was followed by railway transport. The exposure levels in marine transport were the lowest. The TEX concentrations were found to be substantially higher in air-conditioned buses and MTR trains than in other transports, suggesting the existence of additional solvent-related sources in their vehicle interiors. Measurements in non-air-conditioned double deck vehicles indicate that there was slightly higher VOC levels in the lower deck than in the upper deck microenvironment. The average upper to lower deck exposure ratio ranged from 0.79 to 0.87 in trams and 0.78-0.83 in non-air-conditioned buses, depending on the compound of concern. The VOC exposure levels of public transport commuters in Hong Kong are far lower than those in most oversea cities. The experimental concentrations obtained in this study are within the relevant health-protecting limits as stated in the Hong Kong Indoor Air Quality Objective. Influences of recent VOC pollution control measures and local traffic characteristics on in-vehicle level are discussed.     

Indoor levels of volatile organic compounds at Florentine museum environments in Italy

Indoor Air Quality monitoring in cultural institutions is of particular concern to protect these places and the cultural heritage content. An indoor monitoring campaign was performed in three museums in Florence (Italy) to determine the occurrence and levels of volatile organic compounds (VOCs). VOCs of interest included BTEX (benzene, toluene, ethylbenzene, xylenes), terpenes, aldehydes, organic acids, and cyclic volatile methyl siloxanes (cVMS). The most abundant VOCs in all samples analyzed were BTEX, which were strictly related to the traffic source, followed by siloxanes and terpenes. Among BTEX, toluene was always the most abundant followed by xylenes, ethylbenzene, and benzene. cVMS in exhibition rooms with the presence of visitors showed higher values compared to samples collected when the museums were closed. Terpenes showed not only the influence of vegetation-biogenic sources surrounding a museum but could also be related to the wood used for the construction of showcases and furniture and the use of cleaning products. Data obtained also showed the presence of organic acids and aldehydes whose source can be traced back to exhibits themselves and wood-based furniture. Assessing the levels of organic acids in museums is important because, over time, it can cause deterioration of the artifacts.     

Spatial and temporal variation of BTEX in the urban atmosphere of Delhi, India

Benzene, toluene, ethylbenzene and xylene (BTEX) form an important group of aromatic Volatile Organic Compounds (VOCs) because of their role in the tropospheric chemistry and the risk posed by them to human health. Concentrations of BTEX were determined at different sampling points in the ambient air of Delhi in order to investigate their temporal and spatial distributions. Significant positive correlation coefficient (p<0.01) was found between inter-species concentrations at all the sampling locations. Inter-species ratio and Pearson's correlations indicate that gasoline vehicular exhaust could be the major source of BTEX in Delhi. The inter-species ratios exhibit clear seasonal variations indicating differential reactivity of the VOC species in different seasons. Xylenes were found the largest contributor to the ozone formation followed by toluene.     

The effect of wet film thickness on VOC emissions from a finishing varnish

Finishing varnishes, a typical type of oil-based varnishes, are widely used to shine metal, wood trim and cabinet surfaces in Hong Kong. The influence of wet film thickness on volatile organic compound (VOC) emissions from a finishing varnish was studied in an environmental test chamber. The varnish was applied on an aluminium foil with three different wet film thickness (35.2, 69.9 and 107.3 microm). The experimental conditions were 25.0 degrees C, 50.0% relative humidity (RH) with an air exchange rate of 0.5 h(-1). The concentrations of the major VOCs were monitored for the first 10 h. The air samples were collected by canisters and analysed by gas chromatography/mass selective detector (GC/MSD). Six major VOCs including toluene, chlorobenzene, ethylbenzene, m,p-xylene, o-xylene and 1,3,5-trimethylbenzene were identified and quantified. Marked differences were observed for three different film thicknesses. VOC concentrations increased rapidly during the first few hours and then decreased as the emission rates declined. The thicker the wet film, the higher the VOC emissions. A model expression included an exponentially decreasing emission rate of varnish film. The concentration and time data measured in the chamber were used to determine the parameters of empirical emission rate model. The present work confirmed that the film thickness of varnish influenced markedly the concentrations and emissions of VOCs.     

Long-term observations on the influence of groundwater level variations on BTEX concentrations in groundwater

A long-term study on natural attenuation and remediation in soil and groundwater at the former military base Schäferhof-Süd (Niedersachsen) was performed at a former gasoline filling station. At this locality, a large residual source of benzene, toluene, ethylbenzene, xylenes (BTEX) and additional petroleum hydrocarbons is present in the soil. BTEX-concentrations in the groundwater and their correlation with groundwater level variations were monitored for three years. Within the monitoring period, a very dry summer was recorded, which caused the groundwater level to drop by 1.7 m and the BTEX concentrations to increase from 240 µg/l to 1300 µg/l at the site of contamination. The microbial degradation of BTEX was documented by data on consumption of electron acceptors (oxygen, nitrate or sulphate) and production of reduced products (Fe(II), methane). The degradation is further supported by the detection of metabolites. Therefore, the increasing BTEX concentrations were not a consequence of limited biological degradation.     

Source apportionment of volatile organic compounds in Hong Kong homes

Indoor volatile organic compound (VOC) data obtained in 100 Hong Kong homes were analyzed to investigate the nature of emission sources and their contributions to indoor concentrations. A principal component analysis (PCA) showed that off-gassing of building materials, household products, painted wood products, room freshener, mothballs and consumer products were the major sources of VOCs in Hong Kong homes. The source apportionments were then evaluated by using an absolute principal component scores (APCS) technique combined with multiple linear regressions. The results indicated that 76.5 ± 1% (average ± standard error) of the total VOC emissions in Hong Kong homes attributes to the off-gassing of building materials, followed by the room freshener (8 ± 4%), household products (6 ± 2%), mothballs (5 ± 3%) and painted wood products (4 ± 2%). Analysis on the source strength in the monitored homes revealed that although six indoor sources were identified and quantified in the Hong Kong homes, only some homes were responsible for the elevated concentrations of target VOCs emitted from these sources. The findings provide us the mechanism of reducing levels of indoor VOCs and ultimately lead to cost effective reduction in population exposures.     

Source impacts by volatile organic compounds in an industrial city of southern Taiwan

This study investigates source impacts by airborne volatile organic compounds (VOC) at two sites designated for traffic and industry, in the largest industrial area Kaohsiung, southern Taiwan. The samples were collected at the two sites simultaneously during rush and non-rush hours in summer and autumn seasons. Same pattern of VOC groups were found at both sites: most abundant aromatics (78-95%) followed by alkanes (2-16%) and alkenes (0-6%). The BTEX concentration measured at the two sites ranged from 69 to 301 ppbC. Toluene, isopentane, ethylbenzene, and benzene were found to be the most abundant species. Speciation of VOCs was characterized with several skills including principal component factor analysis and BTEX characteristic ratios. Each of the resulted principal factors at the two sites explained over 80% of the VOCs data variance, and indicated that both of the sampling sites were influenced by both traffic and industrial sources with separately different levels. The remarkable patterns of the first two factors described not only the similarity but also the discrepancy at the two sampling sites, in terms of the source impacts. The high T/B ratios (7.56-14.25) observed at the industrial site implied the important impact from mobile emissions. The indicators, m,p-xylene/benzene and o-xylene/benzene, also confirmed the potential source of motor vehicles at both of the sampling sites. Air age assessment showed that more than half of the total observations located in the domain of fresh air. Low X/E ratios implied somewhat aged air mass transported to the sampling sites. The industrial site might not only encounter emissions from the industry sources, but also under unavoidable impact from the traffic sources.     

Seasonal cycle of VOCs in apartments

To assess the adverse health effects of volatile organic compounds (VOCs), epidemiological studies combine the health outcome of individuals with their concomitant VOC exposure. While the latter is representative of the studied period, health effects might also be the result of long-term exposure or emerge in consequence of a peak pollution throughout the year. To address these problems, additional information about the spatiotemporal distribution of VOCs is necessary. The present paper aims at elucidating the spatial and temporal variation of VOC concentrations in Leipzig, Germany. The analysis is based on 1499 indoor and 222 outdoor measurements taken in the period between 1994 and 2001. All data were collected in the frame of epidemiological studies (Diez et al., 1999; Fritz et al., 1998; Schulz et al., 1999). The analysis comprised concentrations of 30 VOCs belonging to the groups of alkanes, cycloalkanes, aromatics, volatile halogenated hydrocarbons, and terpenes. We found that the VOC load in indoor air is, on average, 10 times higher than outdoors. For the studied period there was a clear downward tendency for all VOCs in apartments in Leipzig, except for terpenes which show an upward trend in the period 1996-99. In indoor air we observe an annual cycle for the total VOC concentration as well as the sum concentrations of the above called groups. Highest concentrations occur during the winter months, approximately three times higher than the summer burden. We summarize this finding in a seasonal model, which is fitted to our measurements. Based on the model we develop a procedure for seasonal adjustment, which enables to roughly estimate the annual peak concentration utilizing one monthly observation.     

Mass concentrations of BTEX inside air environment of buses in Changsha,China

In order to estimate the mass concentrations of benzene (B), toluene (T), ethylbenzene (E) and xylenes (X) inside air environment of buses and to analyze the influencing factors of the BTEX pollution levels, 22 public buses were investigated in Changsha, China. The interior air was collected through activated charcoal adsorption tubes and then the air samples were analyzed with thermally desorbed gas chromatograph. The mass concentrations ranged from 21.3 to 106.4 μg/m³ for benzene, from 53.5 to 266.0 μg/m³ for toluene, from 19.6 to 95.9 μg/m³ for ethylbenzene and from 46.9 to 234.8 μg/m³ for xylenes. Their mean values were 68.7, 179.7, 62.5 and 151.8 μg/m³, respectively. The rates of buses tested where the interior concentrations exceeded the limit levels of Chinese Indoor Air Quality Standard were 45.5% for toluene and 13.6% for xylenes. The BTEX levels increased when in-car temperature or relative humidity rose, and decreased when car age or travel distance increased. The BTEX concentrations were higher in leather trims buses than in non-leather trims ones, in air-conditioned buses than in non-air-conditioned ones, and in high-grade buses than in low-grade ones. According to the analysis of multiple linear regression equation, car age and in-car temperature were two most important factors influencing the BTEX pollution levels in the cabins of public buses.     

Spatial and temporal trends of volatile organic compounds (VOC) in a rural area of northern Spain

Ambient concentrations of volatile organic compounds (VOCs) were measured at 40 rural sampling points in Navarre (northern Spain). Air samples were collected by means of sorbent passive sampling and analyzed by thermal desorption (TD) and gas chromatography/mass-selective detector (GC/MSD). A total of 140 VOCs were identified during the study, which was carried out between May to October 2004 for a total of a 10 biweekly sampling campaigns. Concentrations of benzene, toluene, ethylbenzene, m/p-xylenes, o-xylene (BTEX) and 1,3,5-trimethylbenzene were determined in order to investigate their temporal and spatial distributions. Geostatistical analysis pointed to traffic as the main emission source of these compounds. Supporting this idea, BTEX and nitrogen oxides concentrations were found to be highly significantly correlated (r = 0.495, P = 0.001), whereas a strong negative correlation between BTEX and ozone was also observed (r = -0.355, P = 0.025). The concentrations for the BTEX group were similar to the values that have been previously reported for other rural areas.     

Formaldehyde and volatile organic compounds in Hong Kong homes: concentrations and impact factors

Abstract Abstract This paper presents formaldehyde and volatile organic compounds (VOC) concentrations, potential sources and impact factors in 100 homes. The 24‐h average formaldehyde concentration in 37 homes exceeded the good class of the Hong Kong Indoor Air Quality Objectives (HKIAQO), whereas the total VOCs concentration in all homes was lower than the HKIAQO. Compared to other East Asian cities, indoor formaldehyde and styrene in Hong Kong was the highest, reflecting that the homes in Hong Kong were more affected by household products and materials. The formaldehyde concentration in newly built apartments was significantly higher than that in old buildings, whereas no relationship between the concentration and the building age was found for VOCs. There was no difference for formaldehyde and toluene between smoking and non‐smoking homes, suggesting that cigarette smoking was not the major source of these two species. Homes of a couple with a child had higher formaldehyde and acetic acid concentrations, while homes with more than three people had higher concentrations of 1‐butanol, heptane and d‐limonene. When shoes were inside the homes, heptane, acetic acid, nonane and styrene concentrations were statistically higher than that when shoes were out of the homes. Furthermore, higher levels of 1,2,4‐trimethylbenzene, styrene, nonane and heptane were found in gas‐use families rather than in electricity‐use homes.     

Ambient air levels of volatile organic compounds (VOC) and nitrogen dioxide (NO2) in a medium size city in Northern Spain

Ambient concentrations of volatile organic compounds (VOC) and nitrogen dioxide (NO₂) were measured by means of passive sampling at 40 sampling points in a medium-size city in Northern Spain, from June 2006 to June 2007. VOC and NO₂ samplers were analysed by thermal desorption followed by gas chromatography/mass-selective detector and by visible spectrophotometry, respectively. Mean concentrations of benzene, toluene, ethylbenzene, xylenes, propylbenzene, trimethylbenzenes, and NO₂ were 2.84, 13.26, 2.15, 6.01, 0.59, 1.32 and 23.17 µg m^− 3 respectively, and found to be highly correlated. Their spatial distribution showed high differences in small distances and pointed to traffic as the main emission source of these compounds. The lowest levels of VOC and NO₂ occurred during summer, owing to the increase in solar radiation and to lower traffic densities. Mean concentrations of benzene and NO₂ exceeded the European limits at some of the monitored points.     

Carbonaceous characteristics of atmospheric particulate matter in Hong Kong

To determine the characteristic of carbonaceous species in atmospheric particles in Hong Kong, PM₁₀ and PM_2.5 samples were collected using high volume (hi-vol.) air samplers from November 2000 to February 2001. The organic carbon (OC) and elemental carbon (EC) were analyzed by the selective thermal manganese dioxide oxidation (TMO) method. The ratios of PM_2.5/PM₁₀ mass ratios were 0.61, 0.78 and 0.53 for particulate matter collected at PolyU station (PolyU, near a major traffic corridor), Kwun Tong station (KT, mixed residential/commercial/industrial) and the Hok Tsui background station (HT), respectively. These results indicate that the PM_2.5 concentrations constitute the majority of the PM₁₀ concentrations, especially in urban and industrial areas of Hong Kong. The average concentrations at the three sites ranged from 73.11 to 83.52 μg/m³ for PM₁₀ and from 42.37 to 57.38 μg/m³ for PM_2.5. The highest daily mass concentrations of PM₁₀ and PM_2.5 were 125.89 μg/m³ and 116.89 μg/m³ at KT, respectively. The correlation between PM₁₀ and PM_2.5 was high at KT and HT (r>0.9, P<0.01). This means that the sources of PM₁₀ and PM_2.5 may be the same at both sites. The highest mean concentration of OC (12.02 μg/m³) and EC (6.86 μg/m³) in PM₁₀ was found at the PolyU among the three sites. For PM_2.5, the highest mean concentration of OC (10.16 μg/m³) was at KT while the highest mean concentration of EC (7.95 μg/m³) was at PolyU. However, the background concentrations at HT were higher than another background area, Kosan, Korea. Transportation of pollutants from the Asian continent may be responsible for the elevations of EC+OC at the remote site. More than 74% of the EC and more than 79% of the OC were found in the PM_2.5 fraction at the three sampling locations. At PolyU station, PM_2.5 consisted of 18.18% OC and 11.16% EC while 17.70% OC and 8.81% EC were found in KT station. Thus OC and EC are major constituents of aerosols in Hong Kong. OC/EC ratios for PM₁₀ and PM_2.5 were less than 2 at PolyU and KT stations while the ratio exceeded 3 at HT background station. This indicates that OC measured in the urban area may be emitted directly as a primary aerosol.     

Ambient volatile organic compound (VOC) concentrations around a petrochemical complex and a petroleum refinery

Air samples were collected between September 2000 and September 2001 in Izmir, Turkey at three sampling sites located around a petrochemical complex and an oil refinery to measure ambient volatile organic compound (VOC) concentrations. VOC concentrations were 4-20-fold higher than those measured at a suburban site in Izmir, Turkey. Ethylene dichloride, a leaded gasoline additive used in petroleum refining and an intermediate product of the vinyl chloride process in the petrochemical complex, was the most abundant volatile organic compound, followed by ethyl alcohol and acetone. Evaluations based on wind direction clearly indicated that ambient VOC concentrations measured were affected by the refinery and petrochemical complex emissions. VOC concentrations showed seasonal variations at all sampling sites. Concentrations were highest in summer, followed by autumn, probably due to increased evaporation of VOCs from fugitive sources as a result of higher temperatures. VOC concentrations generally increased with temperature and wind speed. Temperature and wind speed together explained 1-60% of the variability in VOC concentrations. The variability in ambient VOC concentrations that could not be explained by temperature and wind speed can be attributed to the effect of other factors (i.e. wind direction, other VOC sources).     

Evaluation of impact factors on VOC emissions and concentrations from wooden flooring based on chamber tests

In this study, the impact factors of temperature, relative humidity (RH), air exchange rate, and volatile organic compound (VOC) properties on the VOC (toluene, n-butyl acetate, ethylbenzene, and m,p-xylene) specific emission rates (SERs) and concentrations from wooden flooring were investigated by chamber test for 8 days. The tested wood in this study is not common solid wood, but composite wood made of combined wood fibers. The experiments were conducted in a stainless-steel environmental test chamber coated with Teflon. The experimental results within 8 days of testing showed that, when the temperature increased from 15 to 30 °C, the VOC SERs and concentrations increased 1.5–129 times. When the RH increased from 50% to 80%, the VOC concentrations and SERs increased 1–32 times. When the air change rate increased from 1 to 2 h⁻¹, the VOC concentrations decreased 9–40%, while the VOC SERs increased 6–98%. The relations between the boiling points of the VOCs and each of the normalized VOC SERs and concentrations were linear with negative slopes. The relations between the vapor pressures of the VOCs and each of the normalized VOC SERs and concentrations were linear with positive slopes. At 15 °C, RH50%, the relations between the diffusivities of VOCs and each of the normalized VOC equilibrium SERs and concentrations were linear with a positive slope.     

Indoor and outdoor carbonyl compounds and BTEX in the hospitals of Guangzhou, China

Indoor and outdoor concentration levels of 21 carbonyl compounds and five BTEX (benzene, toluene, ethylbenzene and xylenes) were measured in four hospitals of Guangzhou from 2nd January to 20th March 2004. Samples were collected in five consecutive daytimes for each hospital. Among most of the samples, acetone was the most abundant carbonyl, followed by acetaldehyde, 2-butanone or formaldehyde. Toluene was the most abundant BTEX and the others were at similar levels. The relatively higher acetone concentrations might have resulted from the high level of background in Guangzhou area due to emission of the factories and LPG-fuel vehicles, and also for the special weather conditions during sampling time. The high concentration of acetaldehyde, which was even higher than that of formaldehyde, might be resulted from the wide use of ethanol in hospital. The partial oxidation of ethanol may form acetaldehyde. The indoor concentrations of carbonyls and BTEX were found a little higher than their outdoor counterparts with only a few exceptions, which showed the anthropogenic sources for these compounds. The low correlations between most carbonyls and BTEX concentrations might be caused by their complex sources. Finally, the human exposure levels of formaldehyde and acetaldehyde in hospitals are discussed.     

Status of the indoor air chemical pollution in Japanese houses based on the nationwide field survey from 2000 to 2005

This paper describes the present state and the changes in indoor air pollution levels by Volatile Organic Compounds (VOCs) in houses in Japan, as revealed through measurements of indoor VOC concentrations and investigations on the actual conditions in the residential environment by means of a questionnaire survey covering a total of more than 10,000 newly built houses over six years (from 2000 to 2005). The VOCs initially measured were formaldehyde, toluene, xylene, and ethylbenzene, followed by the subsequent inclusion of styrene and acetaldehyde.     

Performance test for evaluating the reduction of VOCs in rooms and evaluating the lifetime of sorptive building materials

In this study, we evaluated the effectiveness of sorptive building materials in reducing volatile organic compound (VOC) concentrations in air using a small test chamber. Air containing a low concentration of VOCs was supplied and any decrease in the VOC concentrations was measured at the exhaust. Seven different types of building materials were investigated: activated carbon, gypsum board mixed with a given quantity of activated carbon, board made out of activated carbon, humidity-controlling porous ceramic material, humidity-controlling silicate calcium, ceramic tile and ordinary gypsum board. We examined the sorptive performance on a mix of gases (toluene, ethylbenzene, p-xylene and styrene) in a room. Activated carbon layer was one of the sorptive building materials, and effectively reduced VOC concentrations. We measured the sorption isotherm using the sorption breakthrough capacity test, which is an effective method of evaluating the long-term reduction performance of sorptive building materials and can be measured in a relatively short period of a few hours. Experiments show that sorptive building materials are fairly effective in reducing VOC concentrations in rooms, and that this effect can be expected in practical applications.     

Indoor gaseous air pollutants determinants in office buildings—The OFFICAIR project

The aim of this study was to identify determinants of aldehyde and volatile organic compound (VOC) indoor air concentrations in a sample of more than 140 office rooms, in the framework of the European OFFICAIR research project. A large field campaign was performed, which included (a) the air sampling of aldehydes and VOCs in 37 newly built or recently retrofitted office buildings across 8 European countries in summer and winter and (b) the collection of information on building and offices’ characteristics using checklists. Linear mixed models for repeated measurements were applied to identify the main factors affecting the measured concentrations of selected indoor air pollutants (IAPs). Several associations between aldehydes and VOCs concentrations and buildings’ structural characteristic or occupants’ activity patterns were identified. The aldehyde and VOC determinants in office buildings include building and furnishing materials, indoor climate characteristics (room temperature and relative humidity), the use of consumer products (eg, cleaning and personal care products, office equipment), as well as the presence of outdoor sources in the proximity of the buildings (ie, vehicular traffic). Results also showed that determinants of indoor air concentrations varied considerably among different type of pollutants.