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.     

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.     

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.     

Measurements of the physical properties of particles in the urban atmosphere

Measurements of the physical properties of particles in the atmosphere of a UK urban area have been made, including particle number count by condensation nucleus counters with different lower particle size cut-offs; particle size distributions using a Scanning Mobility Particle Sizer; total particle Fuchs surface area using an epiphaniometer and particle mass using Tapered Element Oscillating Micro-balance (TEOM) instruments with size selective (PM₁₀ and PM_2.5) inlets. Mean particle number counts at three sites range from 2.86×10⁴ to 9.60×10⁴ cm^-3. A traffic-influenced location showed a substantially higher ratio of particle number to PM₁₀ mass than a nearby background location despite being some 70 m from the roadway. Operating two condensation nucleus counters in tandem to determine particles in the 3–7 nm size range by difference showed signficant numbers of particles in this range, apparently related to homogeneous nucleation processes. Measurements with the Scanning Mobility Particle Sizer showed a clear difference between roadside size distributions and those at a nearby background location with an additional mode in the roadside samples below 10 nm diameter. Particle number counts were found to show a significant linear correlation with PM₁₀ mass (r²=0.44; n=44 for 24 h data at an urban background location), although during one period of high pollution a curvilinear relationship was found. Measurements of the diurnal variation in PM₁₀ mass, particle number count and Fuchs surface area show the same general pattern of behaviour of the three variables, explicable in terms of vehicle emission source strength and atmospheric dispersion, although the surface area growth was out of phase with the particle number and mass. It appears that particle number gives the clearest indication of recent road traffic emissions.     

Particulate matter in the indoor air of classrooms—exploratory results from Munich and surrounding area

Numerous epidemiological studies have demonstrated the association between particle mass (PM) concentration in outside air and the occurrence of health related problems and/or diseases. However, much less is known about indoor PM concentrations and associated health risks. In particular, data are needed on air quality in schools, since children are assumed to be more vulnerable to health hazards and spend a large part of their time in classrooms.On this background, we evaluated indoor air quality in 64 schools in the city of Munich and a neighbouring district outside the city boundary. In winter 2004–2005 in 92 classrooms, and in summer 2005 in 75 classrooms, data on indoor air climate parameters (temperature, relative humidity), carbon dioxide (CO₂) and various dust particle fractions (PM₁₀, PM_2.5) were collected; for the latter both gravimetrical and continuous measurements by laser aerosol spectrometer (LAS) were implemented. In the summer period, the particle number concentration (PNC), was determined using a scanning mobility particle sizer (SMPS). Additionally, data on room and building characteristics were collected by use of a standardized form. Only data collected during teaching hours were considered in analysis. For continuously measured parameters the daily median was used to describe the exposure level in a classroom.The median indoor CO₂ concentration in a classroom was 1603 ppm in winter and 405 ppm in summer. With LAS in winter, median PM concentrations of 19.8 μg m⁻³ (PM_2.5) and 91.5 μg m⁻³ (PM₁₀) were observed, in summer PM concentrations were significantly reduced (median PM_2.5=12.7 μg m⁻³, median PM₁₀=64.9 μg m⁻³). PM_2.5 concentrations determined by the gravimetric method were in general higher (median in winter: 36.7 μg m⁻³, median in summer: 20.2 μg m⁻³) but correlated strongly with the LAS-measured results. In explorative analysis, we identified a significant increase of LAS-measured PM_2.5 by 1.7 μg m⁻³ per increase in humidity by 10%, by 0.5 μg m⁻³ per increase in CO₂ indoor concentration by 100 ppm, and a decrease by 2.8 μg m⁻³ in 5–7th grade classes and by 7.3 μg m⁻³ in class 8–11 compared to 1–4th class. During the winter period, the associations were stronger regarding class level, reverse regarding humidity (a decrease by 6.4 μg m⁻³ per increase in 10% humidity) and absent regarding CO₂ indoor concentration. The median PNC measured in 36 classrooms ranged between 2622 and 12,145 particles cm⁻³ (median: 5660 particles cm⁻³).The results clearly show that exposure to particulate matter in school is high. The increased PM concentrations in winter and their correlation with high CO₂ concentrations indicate that inadequate ventilation plays a major role in the establishment of poor indoor air quality. Additionally, the increased PM concentration in low level classes and in rooms with high number of pupils suggest that the physical activity of pupils, which is assumed to be more pronounced in younger children, contributes to a constant process of resuspension of sedimented particles. Further investigations are necessary to increase knowledge on predictors of PM concentration, to assess the toxic potential of indoor particles and to develop and test strategies how to ensure improved indoor air quality in schools.     

Associations between particle physicochemical characteristics and oxidative capacity: An indoor PM10 study in Beijing,China

A study was undertaken to determine the use of a plasmid DNA scission assay to evaluate the causal relationships between particle oxidative capacity and physico-chemistry. Field emission scanning electron microscopy (FESEM), image analysis (IA) and inductively coupled plasma-mass spectrometry (ICP-MS) were employed to investigate the physico-chemical characteristics of indoor PM₁₀ (particulate matter with an aerodynamic diameter of 10 μm or less) in Beijing, China. Six PM₁₀ samples (indoor smoker's living room; indoor non-smoker's living room and kitchen; and outdoor Beijing city; winter versus summer) were selected to represent typical indoor Beijing PM₁₀ environments that contain high particle mass. The PM₁₀ collected from a kitchen and two smoker's homes had the lowest TD₅₀ (toxic dosage of PM₁₀ causing 50% plasmid DNA damage), being as low as 45 μg ml⁻¹ (kitchen) and 100 μg ml⁻¹ (living room), which suggests a high oxidative capacity, with the PM₁₀ generated in kitchens appearing to be the most toxic. The indoor PM₁₀ from the non-smoker's home and outdoor PM₁₀ samples demonstrated high TD₅₀ values and were deemed less bioreactive (i.e. caused limited DNA damage). FESEM observations revealed that four types of particle species were prevalent in Beijing indoor PM₁₀; soot aggregates, minerals, coal fly ash and unknown fine particles. IA showed that higher percentages of soot and unknown fine particles were associated with the lower TD₅₀ values, suggesting that soot and the unknown fine particles may be important components responsible for the observed plasmid DNA damage. The water-soluble trace elements were negatively correlated with the TD₅₀ values, implying that the DNA damage may be attributed to the water-soluble fraction of the PM₁₀. Water-soluble zinc revealed the best relationship with the TD₅₀ values than other analyzed elements, signifying it may play a role in driving the oxidative damage.     

Spatial variation of mass concentration of roadside suspended particulate matter in metropolitan Hong Kong

This study conducted roadside particulate sampling to measure the total suspended particulate (TSP), PM₁₀ (particles <10 μm in aerodynamic diameter) and PM_2.5 (particles <2.5 μm in aerodynamic diameter) mass concentration in 11 urbanized and densely populated districts in Hong Kong. One hundred and thirty-three samples were obtained to measure the mass concentrations of TSP, PM₁₀ and PM_2.5. According to these results, the TSP, PM₁₀ and PM_2.5 mass concentrations varied from 94.85 to 301.63 μg m⁻³, 67.67 to 142.68 μg m⁻³ and 50.01 to 125.12 μg m⁻³, respectively. The PM_2.5/PM₁₀ ratio of all samples was 0.82 which ranged from 0.62 to 0.95. The PM levels and PM ratios in metropolitan Hong Kong significantly fluctuated from site-to-site and over time. The PM_2.5 mass concentration in different districts corresponding to urban industrial, new town, urban residential and urban commercial were 77.64, 87.50, 106.96 and 88.54 μg m⁻³, respectively. The PM_2.5 level is high in Hong Kong, and for individual sampling, more than 60% daily measurements exceeded the NAAQS. The mass fraction of PM_2.5 in PM₁₀ and TSP is relatively high when compared with overseas studies.     

Measurements of fine and ultrafine particles formation in photocopy centers in Taiwan

This study investigates the levels of particulate matter smaller than 2.5 μm (PM_2.5) and some selected volatile organic compounds (VOCs) at 12 photocopy centers in Taiwan from November 2004 to June 2005. The results of BTEXS (benzene, toluene, ethylbenzene, xylenes and styrene) measurements indicated that toluene had the highest concentration in all photocopy centers, while the concentration of the other four compounds varied among the 12 photocopy centers. The average background-corrected eight-hour PM_2.5 in the 12 photocopy centers ranged from 10 to 83 μg m⁻³ with an average of 40 μg m⁻³. The 24-h indoor PM_2.5 at the photocopy centers was estimated and at two photocopy centers exceeded 100 μg m⁻³, the 24-h indoor PM_2.5 guideline recommended by the Taiwan EPA. The ozone level and particle size distribution at another photocopy center were monitored and indicated that the ozone level increased when the photocopying started and the average ozone level at some photocopy centers during business hour may exceed the value (50 ppb) recommended by the Taiwan EPA. The particle size distribution monitored during photocopying indicated that the emitted particles were much smaller than the original toner powders. Additionally, the number concentration of particles that were smaller than 0.5 μm was found to increase during the first hour of photocopying and it increased as the particle size decreased. The ultrafine particle (UFP, <100 nm) dominated the number concentration and the peak concentration appeared at sizes of under 50 nm. A high number concentration of UFP was found with a peak value of 1E+8 particles cm⁻³ during photocopying. The decline of UFP concentration was observed after the first hour and the decline is likely attributable to the surface deposition of charged particles, which are charged primarily by the diffusion charging of corona devices in the photocopier. This study concludes that ozone and UFP concentrations in photocopy centers should be concerned in view of indoor air quality and human health. The corona devices in photocopiers and photocopier-emitted VOCs have the potential to initiate indoor air chemistry during photocopying and result in the formation of UFP.     

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.     

Exposure assessment of air pollutants: a review on spatial heterogeneity and indoor/outdoor/personal exposure to suspended particulate matter,nitrogen dioxide and ozone

This review describes databases of small-scale spatial variations and indoor, outdoor and personal measurements of air pollutants with the main focus on suspended particulate matter, and to a lesser extent, nitrogen dioxide and photochemical pollutants. The basic definitions and concepts of an exposure measurement are introduced as well as some study design considerations and implications of imprecise exposure measurements. Suspended particulate matter is complex with respect to particle size distributions, the chemical composition and its sources. With respect to small-scale spatial variations in urban areas, largest variations occur in the ultrafine (<0.1 μm) and the coarse mode (PM_10–2.5, resuspended dust). Secondary aerosols which contribute to the accumulation mode (0.1–2 μm) show quite homogenous spatial distribution. In general, small-scale spatial variations of PM_2.5 were described to be smaller than the spatial variations of PM₁₀. Recent studies in outdoor air show that ultrafine particle number counts have large spatial variations and that they are not well correlated to mass data. Sources of indoor particles are from outdoors and some specific indoor sources such as smoking and cooking for fine particles or moving of people (resuspension of dust) for coarse particles. The relationships between indoor, outdoor and personal levels are complex. The finer the particle size, the better becomes the correlation between indoor, outdoor and personal levels. Furthermore, correlations between these parameters are better in longitudinal analyses than in cross-sectional analyses. For NO₂ and O₃, the air chemistry is important. Both have considerable small-scale spatial variations within urban areas. In the absence of indoor sources such as gas appliances, NO₂ indoor/outdoor relationships are strong. For ozone, indoor levels are quite small. The study hypothesis largely determines the choice of a specific concept in exposure assessment, i.e. whether personal sampling is needed or if ambient monitoring is sufficient. Careful evaluation of the validity and improvements in precision of an exposure measure reduce error in the measurements and bias in the exposure–effect relationship.     

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.     

Monitoring personal,indoor, and outdoor exposures to metals in airborne particulate matter: Risk of contamination during sampling,handling and analysis

Rigorous sampling and quality assurance protocols are required for the reliable measurement of personal, indoor and outdoor exposures to metals in fine particulate matter (PM_2.5). Testing of five co-located replicate air samplers assisted in identifying and quantifying sources of contamination of filters in the laboratory and in the field. A field pilot study was conducted in Windsor, Ont., Canada to ascertain the actual range of metal content that may be obtained on filter samples using low-flow (4 L min⁻¹) 24-h monitoring of personal, indoor and outdoor air. Laboratory filter blanks and NIST certified reference materials were used to assess contamination, instrument performance, accuracy and precision of the metals determination. The results show that there is a high risk of introducing metal contamination during all stages of sampling, handling and analysis, and that sources and magnitude of contamination vary widely from element to element. Due to the very small particle masses collected on low-flow 24-h filter samples (median 0.107 mg for a sample volume of approximately 6 m³) the contribution of metals from contamination commonly exceeds the content of the airborne particles being sampled. Thus, the use of field blanks to ascertain the magnitude and variability of contamination is critical to determine whether or not a given element should be reported. The results of this study were incorporated into standard operating procedures for a large multiyear personal, indoor and outdoor air monitoring campaign in Windsor.     

Concentrations of ultrafine,fine and PM2.5 particles in three European cities

Total number concentrations, number concentrations of ultrafine (0.01–0.1 μm) and accumulation (0.1–0.5 μm) particles, as well as mass concentration of PM_2.5 particles and blackness of PM_2.5 filters, which is related to Black Smoke were simultaneously monitored in three European cities during the winter period for three and a half months. The purpose of the study was to describe the differences in concentration levels and daily and diurnal variations in particle number and mass concentrations between European cities. The results show statistically significant differences in the concentrations of PM_2.5 and the blackness of the PM_2.5 filters between the cities, but not in the concentrations of ultrafine particles. Daily PM_2.5 levels were found to be poorly correlated with the daily total and ultrafine number concentrations but better correlated with the number concentration of accumulation particles. According to the principal component analysis airborne particulate pollutants seem to be divided into two major source categories, one identified with particle number concentrations and the other related to mass-based information. The present results underline the importance of using both particle number and mass concentrations to evaluate urban air quality.     

The Influences of Ambient Particle Composition and Size on Particle Infiltration in Los Angeles,CA, Residences

Abstract

Particle infiltration is a key determinant of the indoor concentrations of ambient particles. Few studies have examined the influence of particle composition on infiltration, particularly in areas with high concentrations of volatile particles, such as ammonium nitrate (NH₄NO₃). A comprehensive indoor monitoring study was conducted in 17 Los Angeles–area homes. As part of this study, indoor/outdoor concentration ratios during overnight (nonindoor source) periods were used to estimate the fraction of ambient particles remaining airborne indoors, or the particle infiltration factor (F_INF), for fine particles (PM_2.5), its nonvolatile (i.e., black carbon [BC]) and volatile (i.e., nitrate [NO₃ ^?]) components, and particle sizes ranging between 0.02 and 10 μm. F_INF was highest for BC (median = 0.84) and lowest for NO₃ ^? (median = 0.18). The low F_INF for NO₃ ^? was likely because of volatilization of NO₃ ^? particles once indoors, in addition to depositional losses upon building entry. The F_INF for PM_2.5 (median = 0.48) fell between those for BC and NO₃ ^?, reflecting the contributions of both particle components to PM_2.5. F_INF varied with particle size, air-exchange rate, and outdoor NO₃ ^? concentrations. The F_INF for particles between 0.7 and 2 μm in size was considerably lower during periods of high as compared with low outdoor NO₃ ^? concentrations, suggesting that outdoor NO₃ ^? particles were of this size. This study demonstrates that infiltration of PM_2.5 varies by particle component and is lowest for volatile species, such as NH₄NO₃. Our results suggest that volatile particle components may influence the ability for outdoor PM concentrations to represent indoor and, thus, personal exposures to particles of ambient origin, because volatilization of these particles causes the composition of PM_2.5 to differ indoors and outdoors. Consequently, particle composition likely influences observed epidemiologic relationships based on outdoor PM concentrations, especially in areas with high concentrations of NH₄NO₃ and other volatile particles.     

Is remaining indoors an effective way of reducing exposure to fine particulate matter during biomass burning events?

Bushfires, prescribed burns, and residential wood burning are significant sources of fine particles (aerodynamic diameter <2.5 μm; PM_2.5) affecting the health and well-being of many communities. Despite the lack of evidence, a common public health recommendation is to remain indoors, assuming that the home provides a protective barrier against ambient PM_2.5. The study aimed to assess to what extent houses provide protection against peak concentrations of outdoor PM_2.5 and whether remaining indoors is an effective way of reducing exposure to PM_2.5. The effectiveness of this strategy was evaluated by conducting simultaneous week-long indoor and outdoor measurements of PM_2.5 at 21 residences in regional areas of Victoria, Australia. During smoke plume events, remaining indoors protected residents from peak outdoor PM_2.5 concentrations, but the level of protection was highly variable, ranging from 12% to 76%. Housing stock (e.g., age of the house) and ventilation (e.g., having windows/doors open or closed) played a significant role in the infiltration of outdoor PM_2.5 indoors. The results also showed that leaving windows and doors closed once the smoke plume abates trapped PM_2.5 indoors and increased indoor exposure to PM_2.5. Furthermore, for approximately 50% of households, indoor sources such as cooking activities, smoking, and burning candles or incense contributed significantly to indoor PM_2.5.

Implications: Smoke from biomass burning sources can significantly impact on communities. Remaining indoors with windows and doors closed is a common recommendation by health authorities to minimize exposures to peak concentrations of fine particles during smoke plume events. Findings from this study have shown that the protection from fine particles in biomass burning smoke is highly variable among houses, with information on housing age and ventilation status providing an approximate assessment on the protection of a house. Leaving windows closed once a smoke plume abates traps particles indoors and increases exposures.     

Assessment of road users’ elemental carbon personal exposure levels,London, UK

Little is known about particulate elemental carbon (EC) personal exposure levels, a key component of diesel exhaust, specifically in transport microenvironments. A method utilizing the optical properties of EC particles has been applied to personal exposure measurement filter samples. In a series of field studies carried out in London, UK, during 1999–2000 over 400 fine particle (PM_2.5) personal exposure level measurements were taken for journeys in bicycle, bus, car and underground rail transport microenvironments, along three main fixed routes. The particulate EC contribution to the PM_2.5 personal exposure was assessed indirectly by means of an optical technique and with the development and use of a size fraction specific and site-specific calibration curve. In this first EC personal exposure study of transport users geometric mean exposure levels in the summer field campaign were 11.2 μg m⁻³ (GSD=2.7) for cyclists, 13.6 μg m⁻³ (GSD=1.9) for bus passengers and 21.6 μg m⁻³ (GSD=2.1) for car drivers; corresponding exposure levels in the winter were 16.4 μg m⁻³ (GSD=1.8), 18.6 μg m⁻³ (GSD=2.3) and 27.3 μg m⁻³ (GSD=2.0), respectively. EC/PM_2.5 ratios were approximately 0.5–0.6 for bicycle and bus modes and 0.7–0.8 for the car mode. EC/PM_2.5 ratios for different routes ranged from approximately 0.7 for Route 1 to 0.4 for Route 3. Cyclists had the lowest exposure to EC, and car occupants the highest exposure. A large difference in exposure levels between a central high traffic density route and the other less central routes was observed. Particulate EC was a very significant proportion of the total PM_2.5 personal exposure and EC personal exposure levels were considerably higher than reported fixed site monitor EC concentrations.     

Characterisation of fresh particulate vehicular exhausts near a Paris high flow road

Simultaneous continuous measurements of PM_2.5, PM₁₀, black carbon mass (BCae), Black smoke (BS) and particle number density (N) were conducted in the close vicinity of a high traffic road around Paris during a three-month period beginning in August 1997. In parallel some aerosol collection was performed on filters in order to assess the black carbon (BC), organic carbon (OC) and water soluble organic fractions (WSOC) of the freshly emitted traffic aerosols. The high hourly concentrations of PM_2.5 (39±20 μg m⁻³), BCae (14±7 μg m⁻³), and N (220,000±115,000 cm⁻³), were found to be well correlated with each other. On average PM_2.5 represented 66±13% of PM₁₀ and appears to be composed primarily of BC (43±20%). On the contrary no correlation was found between PM_2.5 and the coarse (PM₁₀–PM_2.5) mass fractions which was attributed to resuspension processes by vehicles. Black carbon mass concentrations obtained from both filter analyses (BC) and Aethalometre data (BCae) show a good agreement suggesting that the Aethalometre calibration based on a black carbon specific attenuation coefficient (σ) of 19 m² g⁻¹ is well adapted to nearby roadside measurements. Daily BC (used as a surrogate for fine particles) concentrations and wind speed were found to be anti-correlated. Average daily variations of BC could be related to traffic intensity and regime as well as to the boundary layer height. As expected for freshly emitted traffic aerosols, filter analyses indicated a high BC/TC ratio (29±5%) and a low mean WSOC/OC ratio (12.5±5%) for the bulk aerosol. For these two ratios no day/night differences were observed, the sampling station being probably too close to traffic to evidence photochemical modification of the aerosol phase. Finally, a linear relationship was found between BC and BS hourly concentrations (BC=0.10×BS+1.18; r²=0.93) which offers interesting perspectives to retrieve BC concentrations from existing BS archives.     

Spatial variation of particle number and mass over four European cities

The number of ultrafine particles may be a more health relevant characteristic of ambient particulate matter than the conventionally measured mass. Epidemiological time series studies typically use a central site to characterize human exposure to outdoor air pollution. There is currently very limited information how well measurements at a central site reflect temporal and spatial variation across an urban area for particle number concentrations (PNC).The main objective of the study was to assess the spatial variation of PNC compared to the mass concentration of particles with diameter less than 10 or 2.5 μm (PM₁₀ and PM_2.5).Continuous measurements of PM₁₀, PM_2.5, PNC and soot concentrations were conducted at a central site during October 2002–March 2004 in four cities spread over Europe (Amsterdam, Athens, Birmingham and Helsinki). The same measurements were conducted directly outside 152 homes spread over the metropolitan areas. Each home was monitored during 1 week. We assessed the temporal correlation and the variability of absolute concentrations.For all particle indices, including particle number, temporal correlation of 24-h average concentrations was high. The median correlation for PNC per city ranged between 0.67 and 0.76. For PM_2.5 median correlation ranged between 0.79 and 0.98. The median correlation for hourly average PNC was lower (range 0.56–0.66). Absolute concentration levels varied substantially more within cities for PNC and coarse particles than for PM_2.5. Measurements at the central site reflected the temporal variation of 24-h average concentrations for all particle indices at the selected homes across the urban area. A central site could not assess absolute concentrations across the urban areas for particle number.     

Studies of the coarse particle (2.5–10 μm) component in UK urban atmospheres

An analysis is presented of continuous simultaneous measurement data for PM₁₀ and PM_2.5 using TEOM instruments from five sites in the United Kingdom. The results are analysed specifically in relation to the sources and processes influencing the coarse particle fraction (2.5–10 μm). The data show a generally strong correlation between fine and coarse particle concentrations at all sites, with a generally higher proportion of coarse particles in the dryer months of the year. The one rural site shows a notably lower proportion of coarse particles than the urban and suburban sites. Whilst it is possible to disaggregate the coarse particle concentrations into a component which is diluted by increasing windspeed and a component which increases with windspeed and is hence possibly attributable to wind-induced resuspension processes, the latter is only a minor proportion of the total coarse particle concentration. There are appreciable weekday-to-weekend and day-to-night differences between coarse particle concentrations which are most marked at the urban sites indicative of anthropogenic activities being a source of coarse particles. The clearest indication of the likely predominant source of coarse particles arises from an analysis of a data set derived from an urban street canyon site after subtraction of measurements from a nearby urban background location. The data indicate strong relationships of both fine and coarse incremental particle concentrations in the street canyon with incremental NO_x. If incremental fine particles and coarse particles are attributed to exhaust emissions and vehicle-induced resuspension, respectively, then it may be concluded that vehicle-induced resuspension provides a source strength approximately equal to that of exhaust emissions. An analysis of the coarse particle concentration data suggest that episodes of elevated coarse particle concentrations alone very rarely lead to exceedence of the UK air quality standard for PM₁₀ of 50 μg m⁻³ measured as a 24-h running mean.     

Roadside measurements of fine and ultrafine particles at a major road north of Gothenburg

Particle measurements were conducted at a road site 15 km north of the city of Gothenburg for 3 weeks in June 2000. The size distribution between 10 and 368 nm was measured continuously by using a differential mobility particle sizer (DMPS) system. PM_2.5 was sampled on a daily basis with subsequent elemental analysis using EDXRF-spectroscopy. The road is a straight four-lane road with a speed limit of 90 kph. The road passing the site is flat with no elevations where the vehicles run on a steady workload and with constant speed. The traffic intensity is about 20,000 cars per workday and 13,000 vehicles per day during weekends. The diesel fuel used in Sweden is low in sulphur content (<10 ppm) and therefore the diesel vehicles passing the site contribute less to particle emissions in comparison with other studies. A correlation between PM_2.5 and accumulation mode particles (100–368 nm) was observed. However, no significant correlation was found between number concentrations of ultrafine particles (10–100 nm) and PM_2.5 or the accumulation mode number concentration. The particle distribution between 10 and 368 nm showed great dependency on wind speed and wind direction, where the wind speed was the dominant factor for ultrafine (10–100 nm) particle concentrations. The difference in traffic intensity between workday and weekend together with wind data made it possible to single out the traffic contribution to particle emissions and measure the size distribution. The results presented in combination with previous studies show that both PM_2.5 and the mass of accumulation mode particles are bad estimates for ultrafine particles.