Characteristics of carbonyls: Concentrations and source strengths for indoor and outdoor residential microenvironments in China

Indoor and outdoor carbonyl concentrations were measured simultaneously in 12 urban dwellings in Beijing, Shanghai, Guangzhou, and Xi’an, China in summer (from July to September in 2004) and winter (from December 2004 to February 2005). Formaldehyde was the most abundant indoor carbonyls species, while formaldehyde, acetaldehyde and acetone were found to be the most abundant outdoor carbonyls species. The average formaldehyde concentrations in summer indoor air varied widely between cities, ranging from a low of 19.3 μg m⁻³ in Xi’an to a high of 92.8 μg m⁻³ in Beijing. The results showed that the dwellings with tobacco smoke, incense burning or poor ventilation had significantly higher indoor concentrations of certain carbonyls. It was noticed that although one half of the dwellings in this study installed with low emission building materials or furniture, the carbonyls levels were still significantly high. It was also noted that in winter both the indoor and outdoor acetone concentrations in two dwellings in Guangzhou were significantly high, which were mainly caused by the usage of acetone as industrial solvent in many paint manufacturing and other industries located around Guangzhou and relatively longer lifetime of acetone for removal by photolysis and OH reaction than other carbonyls species. The indoor carbonyls levels in Chinese dwellings were higher than that in dwellings in the other countries. The levels of indoor and ambient carbonyls showed great seasonal differences. Six carbonyls species were carried out the estimation of indoor source strengths. Formaldehyde had the largest indoor source strength, with an average of 5.25 mg h⁻¹ in summer and 1.98 mg h⁻¹ in winter, respectively. However, propionaldehyde, crotonaldehyde and benzaldehyde had the weakest indoor sources.     

The relationship between indoor and outdoor airborne particles in the residential environment

The relationship between indoor and outdoor airborne particles was investigated for 16 residential houses located in a suburban area of Brisbane, Australia. The submicrometer particle numbers were measured using the Scanning Mobility Particle Sizer, the larger particle numbers using the Aerodynamic Particle Sizer and an approximation of PM_2.5 was also measured using a DustTrak. The measurements were conducted for normal and minimum ventilation conditions using simultaneous and non-simultaneous measurement methods designed for the purpose of the study. Comparison of the ratios of indoor to outdoor particle concentrations revealed that while temporary values of the ratio vary in a broad range from 0.2 to 2.5 for both lower and higher ventilation conditions, average values of the ratios were very close to one regardless of ventilation conditions and of particle size range. The ratios were in the range from 0.78 to 1.07 for submicrometer particles, from 0.95 to 1.0 for supermicrometer particles and from 1.01 to 1.08 for PM_2.5 fraction. Comparison of the time series of indoor to outdoor particle concentrations shows a clear positive relationship existing for many houses under normal ventilation conditions (estimated to be about and above 2 h⁻¹), but not under minimum ventilation conditions (estimated to be about and below 1 h⁻¹). These results suggest that for normal ventilation conditions, outdoor particle concentrations could be used to predict instantaneous indoor particle concentrations but not for minimum ventilation, unless air exchange rate is known, thus allowing for estimation of the “delay constant”.     

Particulate matter and manganese exposures in Toronto,Canada

Methylcyclopentadienyl manganese tricarbonyl (MMT) is a manganese-based gasoline additive used to enhance automobile performance. MMT has been used in Canadian gasoline for about 20 yr. Because of the potential for increased levels of Mn in particulate matter resulting from automotive exhausts, a large-scale population-based exposure study (∼1000 participant periods) was conducted in Toronto, Canada, to estimate the distribution of 3-day average personal exposures to particulate matter (PM_2.5 and PM₁₀) and Mn. A stratified, three-stage, two-phase probability, longitudinal sample design of the metropolitan population was employed. Residential indoor and outdoor, and ambient levels (at a fixed site and on a roof) of PM_2.5, PM₁₀, and Mn were also measured. Supplementary data on traffic counts, meteorology, MMT levels in gasoline, personal occupations, and activities (e.g. amount of vehicular usage) were collected. Overall precision (%RSD) for analysis of duplicate co-located samples ranged from 2.5 to 5.0% for particulate matter and 3.1 to 5.5% for Mn. The detection limits were 1.47 and 3.45 μg m^-3 for the PM₁₀ and PM_2.5 fractions, respectively, and 5.50 and 1.83 ng m^-3 for Mn in PM₁₀ and PM_2.5, respectively. These low detection limits permitted the reporting of concentrations for >98% of the samples. For PM₁₀, the personal particulate matter levels (median 48.5 μg m^-3) were much higher than either indoor (23.1 μg m^-3) or outdoor levels (23.6 μg m^-3). The median levels for PM_2.5 for personal, indoor, and outdoor were 28.4, 15.4 and 13.2 μg m^-3, respectively. The correlation between PM_2.5 personal exposures and indoor concentrations was high (0.79), while correlations between personal and the outdoor, fixed site and roof site were low (0.16–0.27). Indoor Mn concentration distributions (in PM_2.5 and PM₁₀), unlike particulate matter, exhibited much lower and less variable levels that the corresponding outdoor data. The median personal exposure was 8.0 ng m^-3, compared with 4.7 and 8.6 ng m^-3, respectively, for the indoor and outdoor distributions. The highest correlations occurred for personal vs indoor data (0.56) and for outdoor vs roof site data (0.66), and vs fixed site data (0.56). The concentration of Mn in particulate matter, expressed in ppm (w/w), revealed that the fixed site was the highest, followed by the roof site, outdoor, indoor, and personal. The personal and indoor data showed a statistically significant correlation (0.68) while all other correlations between personal or indoor data and outdoor or fixed-site data were quite small. The low correlations of personal and indoor levels with outdoor levels suggest that different sources in the indoor and outdoor microenvironments produce particle matter with dissimilar composition. The correlation results indicate that neither the roof- nor fixed-site concentrations can adequately predict personal particulate matter or Mn exposures.     

Participant-based monitoring of indoor and outdoor nitrogen dioxide,volatile organic compounds,and polycyclic aromatic hydrocarbons among MICA-Air households

The Mechanistic Indicators of Childhood Asthma (MICA) study in Detroit, Michigan introduced a participant-based approach to reduce the resource burden associated with collection of indoor and outdoor residential air sampling data. A subset of participants designated as MICA-Air conducted indoor and outdoor residential sampling of nitrogen dioxide (NO₂), volatile organic compounds (VOCs), and polycyclic aromatic hydrocarbons (PAHs). This participant-based methodology was subsequently adapted for use in the Vanguard phase of the U.S. National Children’s Study. The current paper examines residential indoor and outdoor concentrations of these pollutant species among health study participants in Detroit, Michigan.Pollutants measured under MICA-Air agreed well with other studies and continuous monitoring data collected in Detroit. For example, NO₂ and BTEX concentrations reported for other Detroit area monitoring were generally within 10–15% of indoor and outdoor concentrations measured in MICA-Air households. Outdoor NO₂ concentrations were typically higher than indoor NO₂ concentration among MICA-Air homes, with a median indoor/outdoor (I/O) ratio of 0.6 in homes that were not impacted by environmental tobacco smoke (ETS) during air sampling. Indoor concentrations generally exceeded outdoor concentrations for VOC and PAH species measured among non-ETS homes in the study. I/O ratios for BTEX species (benzene, toluene, ethylbenzene, and m/p- and o-xylene) ranged from 1.2 for benzene to 3.1 for toluene. Outdoor NO₂ concentrations were approximately 4.5 ppb higher on weekdays versus weekends. As expected, I/O ratios pollutants were generally higher for homes impacted by ETS.These findings suggest that participant-based air sampling can provide a cost-effective alternative to technician-based approaches for assessing indoor and outdoor residential air pollution in community health studies. We also introduced a technique for estimating daily concentrations at each home by weighting 2- and 7-day integrated concentrations using continuous measurements from regulatory monitoring sites. This approach may be applied to estimate short-term daily or hourly pollutant concentrations in future health studies.     

Behavioral and environmental determinants of personal exposures to PM2.5 in EXPOLIS – Helsinki,Finland

Behavioral and environmental determinants of PM_2.5 personal exposures were analyzed for 201 randomly selected adult participants (25–55 years old) of the EXPOLIS study in Helsinki, Finland. Personal exposure concentrations were higher than respective residential outdoor, residential indoor and workplace indoor concentrations for both smokers and non-smokers. Mean personal exposure concentrations of active smokers (31.0±31.4 μg m⁻³) were almost double those of participants exposed to environmental tobacco smoke (ETS) (16.6±11.8 μg m⁻³) and three times those of participants not exposed to tobacco smoke (9.9±6.2 μg m⁻³). Mean indoor concentrations of PM_2.5 when a member of the household smoked indoors (20.8±23.9 μg m⁻³) were approximately 2.5 times the concentrations of PM_2.5 when no smoking was reported (8.2±5.2 μg m⁻³). Interestingly, however, both mean (8.2 μg m⁻³) and median (6.9 μg m⁻³) residential indoor concentrations for non-ETS exposed participants were lower than residential outdoor concentrations (9.5 and 7.3 μg m⁻³, respectively). In simple linear regression models residential indoor concentrations were the best predictors of personal exposure concentrations. Correlations (r²) between PM_2.5 personal exposure concentrations of all participants, both smoking and non-smoking, and residential indoor, workplace indoor, residential outdoor and ambient fixed site concentrations were 0.53, 0.38, 0.17 and 0.16, respectively. Predictors for personal exposure concentrations of non-ETS exposed participants identified in multiple regression were residential indoor concentrations, workplace concentrations and traffic density in the nearest street from home, which accounted for 77% of the variance. Subsequently, step-wise regression not including residential and workplace indoor concentrations as input (as these are frequently not available), identified ambient PM_2.5 concentration and home location, as predictors of personal exposure, accounting for 47% of the variance. Ambient fixed site PM_2.5 concentrations were closely related to residential outdoor concentrations (r²=0.9, p=0.000) and PM_2.5 personal exposure concentrations were higher in summer than during other seasons. Personal exposure concentrations were significantly (p=0.040) higher for individuals living downtown compared with individuals in suburban family homes. Further analysis will focus on comparisons of determinants between Helsinki and other EXPOLIS centers.     

Potential effects of particulate matter from combustion during services on human health and on works of art in medieval churches in Cyprus

Indoor and outdoor particulate matter (PM_0.3-10) number concentrations were established in two medieval churches in Cyprus. In both churches incense was burnt occasionally during Mass. The highest indoor PM_0.5-1 concentrations compared with outdoors (10.7 times higher) were observed in the church that burning of candles indoors was allowed. Peak indoor black carbon concentration was 6.8 μg m⁻³ in the instances that incense was burning and 13.4 μg m⁻³ in the instances that the candles were burning (outdoor levels ranged between 0.6 and 1.3 μg m⁻³). From the water soluble inorganic components determined in PM₁₀, calcium prevailed in all samples indoors or outdoors, whilst high potassium concentration indoors were a clear marker of combustion. Indoor sources of PM were clearly identified and their emission strengths were estimated via modeling of the results. Indoor estimated PM_0.3-10 mass concentrations exceeded air quality standards for human health protection and for the preservation of works of art.     

Modelling of indoor exposure to nitrogen dioxide in the UK

A dynamic multi-compartment computer model has been developed to describe the physical processes determining indoor pollutant concentrations as a function of outdoor concentrations, indoor emission rates and building characteristics. The model has been parameterised for typical UK homes and workplaces and linked to a time-activity model to calculate exposures for a representative homemaker, schoolchild and office worker, with respect to NO₂. The estimates of population exposures, for selected urban and rural sites, are expressed in terms of annual means and frequency of hours in which air quality standards are exceeded. The annual mean exposures are estimated to fall within the range of 5–21 ppb for homes with no source, and 21–27 ppb for homes with gas cooking, varying across sites and population groups. The contribution of outdoor exposure to annual mean NO₂ exposure varied from 5 to 24%, that of indoor penetration of outdoor air from 17 to 86% and that of gas cooking from 0 to 78%. The frequency of exposure to 1 h mean concentrations above 150 ppb was very low, except for people cooking with gas.     

Levels of outdoor PM2.5, absorbance and sulphur as surrogates for personal exposures among post-myocardial infarction patients in Barcelona,Spain

Outdoor levels of fine particles (PM_2.5; particles <2.5 μm) have been associated with cardiovascular health. Persons with existing cardiovascular disease have been suggested to be especially vulnerable. It is unclear, how well outdoor concentrations of PM_2.5 and its constituents measured at a central site reflect personal exposures in Southern European countries. The objective of the study was to assess the relationship between outdoor and personal concentrations of PM_2.5, absorbance and sulphur among post-myocardial infarction patients in Barcelona, Spain.Thirty-eight subjects carried personal PM_2.5 monitors for 24-h once a month (2–6 repeated measurements) between November 2003 and June 2004. PM_2.5 was measured also at a central outdoor monitoring site. Light absorbance (a proxy for elemental carbon) and sulphur content of filter samples were determined as markers of combustion originating and long-range transported PM_2.5, respectively.There were 110, 162 and 88 measurements of PM_2.5, absorbance and sulphur, respectively. Levels of outdoor PM_2.5 (median 17 μg m³) were lower than personal PM_2.5 even after excluding days with exposure to environmental tobacco smoke (ETS) (median after exclusion 27 μg m³). However, outdoor concentrations of absorbance and sulphur were similar to personal concentrations after exclusion of ETS. When repeated measurements were taken into account, there was a statistically significant association between personal and outdoor absorbance when adjusting for ETS (slope 0.66, p<0.001), but for PM_2.5 the association was weaker (slope 0.51, p=0.066). Adjustment for ETS had little effect on the respective association of S (slope 0.69, p<0.001).Our results suggest that outdoor measurements of absorbance and sulphur can be used to estimate both the daily variation and levels of personal exposures also in Southern European countries, especially when exposure to ETS has been taken into account. For PM_2.5, indoor sources need to be carefully considered.     

Inter-comparison of air pollutant concentrations in different indoor environments in Hong Kong

Indoor air quality in selected indoor environments in Hong Kong such as homes, offices, schools, shopping malls and restaurants were investigated. Average CO₂ levels and total bacteria counts in air-conditioned classrooms, shopping malls and restaurants were comparatively higher than those measured in occupied offices and homes. Elevated CO₂ levels exceeding 1000 ppm and total bacteria counts resulted from high occupancy combined with inadequate ventilation. Average PM₁₀ levels were usually higher indoors than outdoors in homes, shopping malls and restaurants. The highest indoor PM₁₀ levels were observed at investigated restaurants due to the presence of cigarette smoking and extensive use of gas stoves for cooking. The restaurants and shopping malls investigated had higher formaldehyde levels than other indoor environments when building material, smoking and internal renovation work were present. Volatile organic compounds (VOCs) in both indoor and outdoor environments mainly resulted from vehicle exhaust emissions. It was observed that interior decoration work and the use of industrial solvents in an indoor environment could significantly increase the indoor levels of VOCs.     

Polyfluorinated telomers in indoor air of Japanese houses

The fluorotelomer alcohols (FTOHs) have been detected in various environmental compartments, including indoor and outdoor air, in North America and Europe. In our previous studies, FTOHs were detected at a relative higher concentration in outdoor air in the Keihan (Kyoto–Osaka, one of the major industrial zones) area, Japan compared to reported data. The exposure level of FTOHs in indoor air in the Keihan area remains unclear. In the present study, indoor air FTOH concentrations were investigated using a passive air sampler containing activated carbon felts. The indoor air sampling was conducted in 49 households of the Keihan area, during winter and summer 2008. Most samples contained 6:2 FTOH, 8:2 FTOH, 10:2 FTOH and 8:2 FTOAc. The median concentration of 8:2 FTOH (5.84 ng m^?3) was highest among fluorotelomers, followed by those of 10:2 FTOH (1.12 ng m^?3), 6:2 FTOH (0.29 ng m^?3), and others. Significant correlations among fluorotelomers were observed in collected samples. The association between housing conditions and 8:2 FTOH concentrations showed that samples collected from bed rooms have higher 8:2 FTOH concentrations than those collected from other locations. In addition, samples collected in winter showed lower levels of 8:2 FTOH than those collected in summer. These findings suggest that 8:2 FTOH is the predominant component among fluorotelomers in indoor air, and that there are emission sources of fluorotelomers in indoor environments of the Keihan area. Further investigations into the origins of fluorotelomers are needed to evaluate indoor contamination with fluorotelomers.     

Quantification of Saharan dust contribution to PM10 concentrations over Italy during 2003–2005

Italy is frequently affected by Saharan dust intrusions, which result in high PM₁₀ concentrations in the atmosphere and can cause the exceedances of the PM₁₀ daily limits (50 μg m^?3) set by the European Union (EU/2008/50). The estimate of African dust contribution to PM₁₀ concentrations is therefore a key issue in air quality assessment and policy formulation. This study presents a first identification of Saharan dust outbreaks as well as an estimate of the African dust contribution to PM₁₀ concentrations during the period 2003–2005 over Italy. The identification of dust events has been carried out by looking at different sources of information such as monitoring network observations, satellite images, ground measurements of aerosol optical properties, dust model simulations and air mass backward trajectory analysis. The contribution of Saharan dust to PM₁₀ monthly concentrations has been estimated at seven Italian locations. The results are both spatially (with station) and temporally (with month and year) variable, as a consequence of the variability of the meteorological conditions. However, excluding the contribution of severe dust events (21st February 2004, 25th–28th September 2003, 23rd–27th March 2005), the monthly contribution of dust varies approximately between 1 μg m^?3 and 10 μg m^?3 throughout year 2005 and between 1 μg m^?3 and 8 μg m^?3 throughout year 2003. In 2004 the dust concentration is lower than 2003 and 2005 (<5 μg m^?3 at all sites). The reduction in the number of daily exceedances of the limit value (50 μg m^?3) after subtraction of the dust contribution is also calculated at each station: it varies with station between 20% and 50% in 2005 and between 5% and 25% in 2003 and 2004.     

Personal exposure to PM2.5 and element composition—A comparison between outdoor and indoor workers from two Mexican cities

Many individuals work outdoors in the formal and informal economy of the large urban areas in developing countries, where they are potentially exposed for long periods to high concentrations of ambient airborne particulate matter (PM). This study describes the personal exposures to PM of 2.5 μm aerodynamic diameter and smaller (PM_2.5) for a sample of outdoor and indoor workers in two cities, Mexico City and Puebla, in central Mexico.Thirty-six workers in Mexico City and 17 in Puebla were studied. Thirty were outdoor workers (i.e., taxi and bus drivers, street vendors, and vehicle inspectors) and 23 were indoor (office) workers. Their personal exposures to PM_2.5 were monitored for a mean 19-h period. In Mexico City, the street vendors and taxi drivers overall exposures were significantly higher than indoor workers were. In Puebla, bus drivers had a higher overall exposure than vehicle inspectors or indoor workers. Most of the exposures were above the 65 μg m⁻³ 24-h Mexican standard.In Mexico City, exposures to Si, Ti, Cr, Mn, Fe, Ni, Cu, Mo and Cd were higher for outdoor than for indoor workers. In Puebla, exposures to Si, S, K, Ca, Ti, V, Mn, and Zn also were higher for outdoor workers. In Mexico City outdoor workers exposures to Cu, Pb, Cr, Se and Mo were 4 or more times higher than for Puebla outdoor workers, while Puebla outdoor workers’ exposures to V, Si, Fe and Ca were 3 or more times higher than Mexico City outdoor workers.These results suggest that for these outdoor workers the elevated local ambient air PM concentrations and an extended period spent outside are more important contributors to total exposures than indoor concentrations. These workers could be at particular risk of increased morbidity and mortality associated with ambient PM.     

Comparison of indoor and outdoor concentrations of CO at a public school. Evaluation of an indoor air quality model

A field study was carried out to investigate the internal and external carbon monoxide (CO) concentration levels of a public school building in Athens, Greece. Simultaneous measurements of indoor and outdoor CO concentrations were conducted using a non-dispersive infrared analyzer. Measurements of mean hourly CO concentrations inside and outside the sampling room were conducted on a 24-h basis for 13 consecutive days during May and June 1999 and for 14 consecutive days during December 1999. The aim of the study was to investigate the attenuation pattern of external pollution levels within the building. The diurnal concentration variations reported for different days during the week show that indoor CO concentrations are in general lower than the respective outdoor levels, and that the morning peaks of indoor concentrations show a delay of 1 h or less compared to the morning peaks of outdoor concentrations. The measured indoor to outdoor concentration ratios show a seasonal variation. An indoor air quality model for the prediction of indoor concentration levels developed by Hayes (J. Air Pollut. Control Assoc. 39 (11) (1989) 1453; J. Air Waste Manage. Assoc. 41 (2) (1991) 161) is coded as a computer program and evaluated using the experimental data. The model results are in good agreement with the indoor concentration measurements, although in some cases the model cannot respond adequately to sharp outdoor concentration changes. The ratio between measured and predicted daily maximum indoor concentration ranges between 0.88 and 1.23. The regression curve between predicted by the model and measured hourly indoor concentrations, for a continuous period of 96 h, has a slope of 0.64 and a coefficient of determination (R²) of 0.69.     

Benzene exposure in Helsinki,Finland

Personal exposures and microenvironmental concentrations of benzene were measured in the residential indoor, residential outdoor and workplace environments for 201 participants in Helsinki, Finland, as a component of the EXPOLIS-Helsinki study. Median benzene personal exposures were 2.47 (arithmetic standard deviation (ASD)=1.62) μg m⁻³ for non-smokers, 2.89 (ASD=3.26) μg m⁻³ for those exposed to environmental tobacco smoke in any microenvironment and 3.08 (ASD=10.04) μg m⁻³ for active smokers. Median residential indoor benzene concentrations were 3.14 (ASD=1.51) μg m⁻³ and 1.87 (ASD=1.93) μg m⁻³ for environments with and without tobacco smoke, respectively. Median residential outdoor benzene concentrations were 1.51 (ASD=1.11) μg m⁻³ and median workplace benzene concentrations were 3.58 (ASD=1.96) μg m⁻³ and 2.13 (ASD=1.49) μg m⁻³ for environments with and without tobacco smoke, respectively. Multiple step-wise regression identified indoor benzene concentrations as the strongest predictor for personal benzene exposures of those not exposed to tobacco smoke, followed sequentially by time spent in a car, time in the indoor environment, indoor workplace concentrations and time in the home workshop. Relationships between indoor and outdoor microenvironment concentrations and personal exposures showed considerable variation between seasons, due to differences in ventilation patterns of homes in these northern latitudes. Automobile use-related activities were significantly associated with elevated benzene levels in personal and indoor measurements when tobacco smoke was not present, which demonstrates the importance of personal measurements in the assessment of exposure to benzene.     

Annual evolution and generation mechanisms of particulate nitrate in Madrid

During the course of one year (March 2004–March 2005), PM_2.5 particulate nitrate concentrations were semi-continuously measured every 10 min at a Madrid suburban site using the Rupprecht and Patashnick Series 8400N Ambient Particulate Nitrate Monitor (8400N). Gaseous pollutants (NO, NO₂, O₃, HCHO, HNO₂) were simultaneously measured with a DOAS spectrometer (OPSIS AR-500) and complementary meteorological information was obtained by a permanent tower. The particulate nitrate concentrations ranged from the instrumental detection limit of around 0.2 μg m⁻³, up to a maximum of about 25 μg m⁻³. The minimum monthly average was reached during August (0.32 μg m⁻³) and the maximum during November (3.0 μg m⁻³). Due to the semi-volatile nature of ammonium nitrate, peaks were hardly present during summer air pollution episodes. A typical pattern during days with low dispersive conditions was characterized by a steep rise of particulate nitrate in the morning, reaching maximum values between 9 and 14 UTC, followed by a decrease during the evening. On some occasions a light increase was observed at nighttime. During spring episodes, brief diurnal nitrate peaks were recorded, while during the autumn and winter episodes, later and broader nitrate peaks were registered. Analysis of particulate nitrate and related gaseous species indicated the photo-chemical origin of the morning maxima, delayed with respect to NO and closely associated with secondary NO₂ maximum values. The reverse evolution of nitrate and nitrous acid was observed after sunrise, suggesting a major contribution from HNO₂ photolysis to OH formation at this time of the day, which would rapidly produce nitrate in both gaseous and particulate phase. Some nocturnal nitrate maxima appeared under high humidity conditions, and a discussion about their origin involving different possible mechanisms is presented, i.e. the possibility that these nocturnal maximum values could be related to the heterogeneous formation of nitrous and nitric acid by the hydrolysis of NO₂ on wet aerosols.     

Bus,minibus, metro inter-comparison of commuters’ exposure to air pollution in Mexico City

Commuters’ exposure measurements were taken for PM_2.5, carbon monoxide (CO) and benzene in minibuses, buses and metro during morning and evening rush hours during January–March 2003 in Mexico City. For PM_2.5, the chemical composition was characterized. Total carbon was the most abundant species in fine particles (approximately 50%). Minibuses (49 μg m⁻³) and buses had similar concentrations of exposure for PM_2.5 (53 μg m⁻³). For CO and benzene the concentrations were higher in minibuses. Morning rush hour was the commuting period with the highest concentrations for minibuses and buses. Metro was the mode of transport with lower concentrations for all pollutants. Carbon monoxide concentrations were similar to those identified in a previous campaign in 2002 and approximately 3.5 times lower than those in a study conducted in 1991. Benzene was characterized systematically in the selected modes of transport. A strong association was observed between wind speed and pollutant concentrations in buses.     

Personal exposures to NO2 in the EXPOLIS-study: relation to residential indoor,outdoor and workplace concentrations in Basel,Helsinki and Prague

Personal exposures, residential indoor, outdoor and workplace levels of nitrogen dioxide (NO₂) were measured for 262 urban adult (25–55 years) participants in three EXPOLIS centres (Basel; Switzerland, Helsinki; Finland, and Prague; Czech Republic) using passive samplers for 48-h sampling periods during 1996–1997. The average residential outdoor and indoor NO₂ levels were lowest in Helsinki (24±12 and 18±11 μg m⁻³, respectively), highest in Prague (61±20 and 43±23 μg m⁻³), with Basel in between (36±13 and 27±13 μg m⁻³). Average workplace NO₂ levels, however, were highest in Basel (36±24 μg m⁻³), lowest in Helsinki (27±15 μg m⁻³), with Prague in between (30±18 μg m⁻³). A time-weighted microenvironmental exposure model explained 74% of the personal NO₂ exposure variation in all centres and in average 88% of the exposures. Log-linear regression models, using residential outdoor measurements (fixed site monitoring) combined with residential and work characteristics (i.e. work location, using gas appliances and keeping windows open), explained 48% (37%) of the personal NO₂ exposure variation. Regression models based on ambient fixed site concentrations alone explained only 11–19% of personal NO₂ exposure variation. Thus, ambient fixed site monitoring alone was a poor predictor for personal NO₂ exposure variation, but adding personal questionnaire information can significantly improve the predicting power.     

Rapid measurements and mapping of tracer gas concentrations in a large indoor space

Rapid mapping of gas concentrations in air benefits studies of atmospheric phenomena ranging from pollutant dispersion to surface layer meteorology. Here we demonstrate a technique that combines multiple-open-path tunable-diode-laser spectroscopy and computed tomography to map tracer gas concentrations with approximately 0.5 m spatial and 7 s temporal resolution. Releasing CH₄ as a tracer gas in a large (7 m×9 m×11 m high) ventilated chamber, we measured path-integrated CH₄ concentrations over a planar array of 28 “long” (2–10 m) optical paths, recording a complete sequence of measurements every 7 s during the course of hour-long experiments. Maps of CH₄ concentration were reconstructed from the long path data using a computed tomography algorithm that employed simulated annealing to search for a best fit solution. The reconstructed maps were compared with simultaneous measurements from 28 “short” (0.5 m) optical paths located in the same measurement plane. On average, the reconstructed maps capture ∼74% of the variance in the short path measurements. The accuracy of the reconstructed maps is limited, in large part, by the number of optical paths and the time required for the measurement. Straightforward enhancements to the instrumentation will allow rapid mapping of three-dimensional gas concentrations in indoor and outdoor air, with sub-second temporal resolution.     

The effects of evaporating essential oils on indoor air quality

Essential oils, predominantly comprised of a group of aromatic chemicals, have attracted increasing attention as they are introduced into indoor environments through various forms of consumer products via different venues. Our study aimed to characterize the profiles and concentrations of emitted volatile organic compounds (VOCs) when evaporating essential oils indoors. Three popular essential oils in the market, lavender, eucalyptus, and tea tree, based on a nation-wide questionnaire survey, were tested. Specific aromatic compounds of interest were sampled during evaporating the essential oils, and analyzed by GC-MS. Indoor carbon monoxide (CO), carbon dioxide (CO₂), total volatile organic compounds (TVOCs), and particulate matters (PM₁₀) were measured by real-time, continuous monitors, and duplicate samples for airborne fungi and bacteria were collected in different periods of the evaporation. Indoor CO (average concentration 1.48 vs. 0.47 ppm at test vs. background), CO₂ (543.21 vs. 435.47 ppm), and TVOCs (0.74 vs. 0.48 ppm) levels have increased significantly after evaporating essential oils, but not the PM₁₀ (2.45 vs. 2.42 ppm). The anti-microbial activity on airborne microbes, an effect claimed by the use of many essential oils, could only be found at the first 30–60 min after the evaporation began as the highest levels of volatile components in these essential oils appeared to emit into the air, especially in the case of tea tree oil. High emissions of linalool (0.092–0.787 mg m⁻³), eucalyptol (0.007–0.856 mg m⁻³), d-limonene (0.004–0.153 mg m⁻³), ρ-cymene (0.019–0.141 mg m⁻³), and terpinene-4-ol-1 (0.029–0.978 mg m⁻³), all from the family of terpenes, were observed, and warranted for further examination for their health implications, especially for their potential contribution to the increasing indoor levels of secondary pollutants such as formaldehyde and secondary organic aerosols (SOAs) in the presence of ozone.     

A functional group characterization of organic PM2.5 exposure: Results from the RIOPA study

The functional group (FG) composition of urban residential outdoor, indoor, and personal fine particle (PM_2.5) samples is presented and used to provide insights relevant to organic PM_2.5 exposure. PM_2.5 samples (48 h) were collected during the Relationship of Indoor, Outdoor, and Personal Air (RIOPA) study at 219 non-smoking homes (once or twice) in Los Angeles County, CA, Elizabeth, NJ, and Houston, TX. Fourier transform infrared (FTIR) spectra of PM_2.5 samples were collected, and FG absorbances were quantified by partial least squares (PLS) regression, a multivariate calibration method.There is growing evidence in the literature that a large majority of indoor-generated PM_2.5 is organic. The current research suggests that indoor-generated PM_2.5 is enriched in aliphatic carbon–hydrogen (CH) FGs relative to ambient outdoor PM_2.5. Indoor-generated CH exceeded outdoor-generated CH in 144 of the 167 homes for which indoor or outdoor CH was measurable; estimated indoor emission rates are provided. The strong presence of aliphatic CH FGs in indoor PM_2.5 makes particulate organic matter substantially less polar indoors and in personal exposures than outdoors. This is a substantial new finding. Based on the quantified FGs, the average organic molecular weight (OM) per carbon weight (OC), a measure of the degree of oxygenation of organic PM, is in the range of 1.7–2.6 for outdoor samples and 1.3–1.7 for indoor and personal samples. Polarity or degree of oxygenation effects particle deposition in exposure environments and in the respiratory system.