北京市冬季住宅内PM_(2.5)暴露水平及室内外关系的研究

目的研究自然通风条件下大规模人群的住宅内PM_(2.5)浓度水平,探讨PM_(2.5)浓度的室内外关系,为评估室内PM_(2.5)暴露提供重要数据支撑和新的研究思路。方法于2013年12月1日—2014年2月28日(2013—2014冬季)在北京市某区开展大规模人群的时间-活动模式和空气污染暴露影响因素调查,基于调查数据及PM_(2.5)空气动力学特性建立住宅内PM_(2.5)的质量平衡模型,利用环境监测站点PM_(2.5)监测数据模拟住宅内PM_(2.5)浓度,计算室内外PM_(2.5)浓度比(I/O),并探讨PM_(2.5)室内外关系。结果本研究1 092个样本2013—2014冬季住宅内PM_(2.5)浓度范围为26~167μg/m~3,PM_(2.5)浓度的中位数为73μg/m~3,四分位数间距为34μg/m~3。室外PM_(2.5)浓度范围分别为0~33μg/m~3、34~65μg/m~3、66~129μg/m~3、≥130μg/m~3时,PM_(2.5)浓度I/O分别为1.75、1.05、0.76和0.63;随着室外PM_(2.5)浓度的增加,I/O呈减小趋势,且分布趋于集中。结论基于大规模人群的时间-活动模式和空气污染暴露影响因素调查建立质量平衡模型,可实现大规模人群室内PM_(2.5)浓度的连续模拟。     

The effect of outdoor air and indoor human activity on mass concentrations of PM(10), PM(2.5), and PM(1) in a classroom

The 12-h mass concentration of PM₁₀, PM_2.5, and PM₁ was measured in a lecturing room by means of three co-located Harvard impactors. The filters were changed at 8 AM and at 8 PM to cover the periods of presence and absence of students. Concentrations were assessed by gravimetry. Ambient PM₁₀ data were available for corresponding 12-h intervals from the nearest state air-quality-monitoring network station. The data were pooled into four periods according to the presence and absence of students—Monday-Thursday day (workday daytime), Monday-Thursday night (workday night), Friday-Sunday day (weekend daytime), and Friday-Sunday night (weekend night). Average indoor workday daytime concentrations were 42.3, 21.9 and 13.7 μg m⁻³, workday night were 20.9, 19.1 and 15.2 μg m⁻³, weekend daytime were 21.9, 18.1 and 11.4 μg m⁻³, and weekend night were 24.5, 21.3, and 15.6 μg m⁻³ for PM₁₀, PM_2.5, and PM₁, respectively. The highest 12-h mean, median, and maximum (42.3, 43.0, and 76.2 μg m⁻³, respectively) indoor concentrations were recorded on workdays during the daytime for PM₁₀. The statistically significant (r=0.68,P<0.0009) correlation between the number of students per hour per day and the indoor coarse fraction calculated as PM_10−2.5 during daytime on workdays indicates that the presence of people is an important source of coarse particles indoor. On workdays, the daytime PM₁₀ indoor/outdoor ratio was positively associated (r=0.93) with an increasing indoor coarse fraction (PM_10-2.5), also indicating that an important portion of indoor PM₁₀ had its source inside the classroom. With the exception of the calculated coarse fraction (PM_10-2.5), all of the measured indoor particulate matter fractions were significantly highly correlated with outdoor PM₁₀ and negatively correlated with wind velocity, showing that outdoor levels of particles influence their indoor concentrations.     

Exposure to fine particles (PM2.5 and PM1) and black smoke in the general population: personal, indoor, and outdoor levels

Personal exposure to PM(2.5) and PM(1), together with indoor and residential outdoor levels, was measured in the general adult population (30 subjects, 23-51 years of age) of Gothenburg, Sweden. Simultaneously, urban background concentrations of PM(2.5) were monitored with an EPA WINS impactor. The 24-h samples were gravimetrically analyzed for mass concentration and black smoke (BS) using a smokestain reflectometer. Median levels of PM(2.5) were 8.4 microg/m(3) (personal), 8.6 microg/m(3) (indoor), 6.4 microg/m(3) (residential outdoor), and 5.6 microg/m(3) (urban background). Personal exposure to PM(1) was 5.4 microg/m(3), while PM(1) indoor and outdoor levels were 6.2 and 5.2 microg/m(3), respectively. In non-smokers, personal exposure to PM(2.5) was significantly higher than were residential outdoor levels. BS absorption coefficients were fairly similar for all microenvironments (0.4-0.5 10(-5) m(-1)). Personal exposure to particulate matter (PM) and BS was well correlated with indoor levels, and there was an acceptable agreement between personal exposure and urban background concentrations for PM(2.5) and BS(2.5) (r(s)=0.61 and 0.65, respectively). PM(1) made up a considerable amount (70-80%) of PM(2.5) in all microenvironments. Levels of BS were higher outdoors than indoors and higher during the fall compared with spring. The correlations between particle mass and BS for both PM(2.5) vs. BS(2.5) and PM(1) versus BS(1) were weak for all microenvironments including personal exposure. The urban background station provided a good estimate of residential outdoor levels of PM(2.5) and BS(2.5) within the city (r(s)=0.90 and 0.77, respectively). Outdoor levels were considerably affected by long-range transported air pollution, which was not found for personal exposure or indoor levels. The within-individual (day-to-day) variability dominated for personal exposure to both PM(2.5) and BS(2.5) in non-smokers.     

Particulate matter measurements PM2.5 and PM10 in Rome: comparison indoor/outdoor

The concentration of airborne particulate matter (PM2.5 and PM10) was assessed over 12 months (1999-2000) both outdoor and indoor (workplaces and homes without major PM sources) through a manual gravimetric method. Mean concentration values outdoors were moderately lower than indoor concentrations in summer, but higher in winter. The correlations between outdoor and indoor values are statistically significant, especially for PM2.5 in winter. The position of indoor sites with respect to street level was immaterial as far as mean values is concerned, whilst maximum values presented some differences accordingly. Day-to-day variability was higher outside than inside, especially in winter. The PM2.5/PM10 ratio was higher indoors, probably owing to the higher sedimentation speed of the coarse fraction.     

Estimating effects of ambient PM(2.5) exposure on health using PM(2.5) component measurements and regression calibration

Most air pollution and health studies conducted in recent years have examined how a health outcome is related to pollution concentrations from a fixed outdoor monitor. The pollutant effect estimate in the health model used indicates how ambient pollution concentrations are associated with the health outcome, but not how actual exposure to ambient pollution is related to health. In this article, we propose a method of estimating personal exposures to ambient PM(2.5) (particulate matter less than 2.5 microm in diameter) using sulfate, a component of PM(2.5) that is derived primarily from ambient sources. We demonstrate how to use regression calibration in conjunction with these derived values to estimate the effects of personal ambient PM(2.5) exposure on a continuous health outcome, forced expiratory volume in 1 s (FEV(1)), using repeated measures data. Through simulation, we show that a confidence interval (CI) for the calibrated estimator based on large sample theory methods has an appropriate coverage rate. In an application using data from our health study involving children with moderate to severe asthma, we found that a 10 microg/m3 increase in PM(2.5) was associated with a 2.2% decrease in FEV(1) at a 1-day lag of the pollutant (95% CI: 0.0-4.3% decrease). Regressing FEV(1) directly on ambient PM(2.5) concentrations from a fixed monitor yielded a much weaker estimate of 1.0% (95% CI: 0.0-2.0% decrease). Relatively small amounts of personal monitor data were needed to calibrate the estimate based on fixed outdoor concentrations.     

Formaldehyde levels in Sweden: personal exposure, indoor, and outdoor concentrations

Formaldehyde is a ubiquitous environmental pollutant and is probably carcinogenic to humans. Exposure to formaldehyde was investigated in the general population with personal as well as stationary measurements. The results from two campaigns in two Swedish cities are presented, including measurements of personal exposure among a total of 65 randomly selected subjects together with simultaneous measurements of individual indoor and outdoor concentrations. Diffusive GMD samplers were placed in the breathing zone, in the participants' bedrooms, and outside their homes for 24 h in campaign A and six days in campaign B. Repeated measurements were also conducted in order to study the variability between and within individuals. Median personal exposure to formaldehyde was 22 microg/m(3) (campaign A) and 23 microg/m(3) (campaign B), which is within the guideline value range of 12-60 microg/m(3) proposed in Sweden. Bedroom concentrations were generally slightly higher than personal exposure, while outdoor concentrations (measured only in campaign B) were low. In campaign B, the stationary measurements were used to model personal exposure. Bedroom concentrations were found to explain 90% of the variation of the measured personal exposure and predicted personal exposure nearly as well as an extended model that also included the outdoor contribution. Subjects living in single-family houses had significantly higher exposure to formaldehyde compared with subjects living in apartments. The 24-h and 6-day sampling periods yield a relatively low within-individual variability for formaldehyde measurements with GMD samplers.     

The relationships between personal PM exposures for elderly populations and indoor and outdoor concentrations for three retirement center scenarios.

Personal exposures, indoor and outdoor concentrations, and questionnaire data were collected in three retirement center settings, supporting broader particulate matter (PM)--health studies of elderly populations. The studies varied geographically and temporally, with populations studied in Baltimore, MD in the summer of 1998, and Fresno, CA in the winter and spring of 1999. The sequential nature of the studies and the relatively rapid review of the mass concentration data after each segment provided the opportunity to modify the experimental designs, including the information collected from activity diary and baseline questionnaires and influencing factors (e.g., heating, ventilation, and air-conditioning (HVAC) system operation, door and window openings, air exchange rate) measurements. This paper highlights both PM2.5 and PM10 personal exposure data and interrelationships across the three retirement center settings, and identifies the most probable influencing factors. The current limited availability of questionnaire results, and chemical speciation data beyond mass concentration for these studies, provided only limited capability to estimate personal exposures from models and apportion the personal exposure collections to their sources. The mean personal PM2.5 exposures for the elderly in three retirement centers were found to be consistently higher than the paired apartment concentrations by 50% to 68%, even though different facility types and geographic locations were represented. Mean personal-to-outdoor ratios were found to 0.70, 0.82, and 1.10, and appeared to be influenced by the time doors and windows were open and aggressive particle removal by the HVAC systems. Essentially identical computed mean PM2.5 personal clouds of 3 micrograms/m3 were determined for two of the studies. The proposed significant contributing factors to these personal clouds were resuspended particles from carpeting, collection of body dander and clothing fibers, personal proximity to open doors and windows, and elevated PM levels in nonapartment indoor microenvironments.     

Modeling the residential infiltration of outdoor PM(2.5) in the Multi-Ethnic Study of Atherosclerosis and Air Pollution (MESA Air)

Background: Epidemiologic studies of fine particulate matter [aerodynamic diameter ≤ 2.5 μm (PM_2.5)] typically use outdoor concentrations as exposure surrogates. Failure to account for variation in residential infiltration efficiencies (F_inf) will affect epidemiologic study results.Objective: We aimed to develop models to predict F_inf for > 6,000 homes in the Multi-Ethnic Study of Atherosclerosis and Air Pollution (MESA Air), a prospective cohort study of PM_2.5 exposure, subclinical cardiovascular disease, and clinical outcomes.Methods: We collected 526 two-week, paired indoor–outdoor PM_2.5 filter samples from a subset of study homes. PM_2.5 elemental composition was measured by X-ray fluorescence, and F_inf was estimated as the indoor/outdoor sulfur ratio. We regressed F_inf on meteorologic variables and questionnaire-based predictors in season-specific models. Models were evaluated using the R² and root mean square error (RMSE) from a 10-fold cross-validation.Results: The mean ± SD F_inf across all communities and seasons was 0.62 ± 0.21, and community-specific means ranged from 0.47 ± 0.15 in Winston-Salem, North Carolina, to 0.82 ± 0.14 in New York, New York. F_inf was generally greater during the warm (> 18°C) season. Central air conditioning (AC) use, frequency of AC use, and window opening frequency were the most important predictors during the warm season; outdoor temperature and forced-air heat were the best cold-season predictors. The models predicted 60% of the variance in 2-week F_inf, with an RMSE of 0.13.Conclusions: We developed intuitive models that can predict F_inf using easily obtained variables. Using these models, MESA Air will be the first large epidemiologic study to incorporate variation in residential F_inf into an exposure assessment.     

室内外PM_(2.5)污染水平对慢性阻塞性肺疾病患者呼出气炎症指标的影响

目的探讨冬季室内外PM_(2.5)污染水平对慢性阻塞性肺疾病(简称慢阻肺)患者呼出气炎症指标的影响。方法以18名某三甲医院诊断的稳定期慢阻肺患者为研究对象,于2014年1月2日—2月18日,对研究对象室内PM_(2.5)水平进行实时监测,同步收集研究对象居室附近北京市固定监测点PM_(2.5)、气温和相对湿度数据,并采集研究对象呼出气一氧化氮(e NO)和呼出气硫化氢(e H2S)样品,采用Spearman相关分析和多元线性回归分析探讨室内外PM_(2.5)对研究对象呼出气指标的影响。结果调查地区冬季室内、外PM_(2.5)污染水平较高,x±s分别为(94.09±46.87)μg/m3和(119.27±54.78)μg/m3。室外PM_(2.5)暴露与e NO呈正相关关系(rs=0.311,P0.05),PM_(2.5)每上升1个四分位数间距(74.80μg/m3),可使e NO增加13.13μg/m3(P0.05),控制室外气温和相对湿度后,该相关关系仍然存在。未观察到室内PM_(2.5)与e NO以及室内、外PM_(2.5)与e H2S的相关关系。结论本次调查地区的冬季室内、外PM_(2.5)污染严重,室外PM_(2.5)可对慢阻肺患者e NO产生影响。     

Concentrations of PM(2.5) mass and components in residential and non-residential indoor microenvironments: the Sources and Composition of Particulate Exposures study

Although short in duration, air pollutant exposures occurring in non-residential microenvironments (MEs), including restaurants, vehicles and commercial locations, can represent a large fraction of total personal exposures. For the Sources and Composition of Particulate Exposures study, a novel compact sampling system was developed, facilitating simultaneous measurement of highly speciated PM(2.5) mass in a range of commercial and residential locations. This sampler also included 1-min measurements of PM(2.5) mass and ultrafine particle (UFP) counts. Sampling was conducted in a number of MEs (retail stores, restaurants and vehicles) throughout Atlanta. Chemically resolved particulate measurements in these locations are of interest for both exposure scientists and epidemiologists but have typically not been conducted because of logistical constraints associated with sampling these trace constituents. We present measurements from a non-random sample of locations that are limited in their generalizability but provide several promising hypothesis-generating results. PM(2.5) mass concentrations greater than 100 μg/m(3), and UFPs>10(5) particles /cm(3) were measured during several events in the restaurant and vehicle. Somewhat unexpectedly, the grocery store ME, along with the restaurant and vehicle, also had the highest levels of elemental carbon (EC), organic carbon (OC) and most elements. In-vehicle concentrations of soil-related elements (Al, Ca, Fe, K and Ti) and auto-related elements (EC, OC, Zn and Cu) were higher than those measured at a central ambient site. The lowest concentrations for most pollutants were found in the hospital and retail locations. It is questionable whether periodic, high PM concentrations in the grocery store and restaurant pose health risks for customers; however, individuals working in these locations may be exposed to levels of concern.     

华中某市居民住宅室内外PM_(2.5)与PM_(10)日变化规律及防护建议

目的了解冬季住宅室内、外PM2.5和PM10浓度日变化规律,指导居民日常防护。方法在灰霾严重的冬季,对华中某市区3个居民住宅室内、外PM2.5和PM10浓度连续监测5 d,绘制出日变化曲线图。结果 PM2.5和PM10浓度日变化呈现一高峰两小峰形态,高峰时段出现在早晨6:00~9:00,两小峰在中午12:00~14:00和傍晚17:00~19:00;室内、外PM2.5和PM10浓度均超过国家环境空气质量二级标准,但室内浓度显著低于室外(P0.01)。结论老人和儿童冬季应减少户外运动或选择适宜时段;患有心血管、呼吸系统疾病及长期从事户外工作的人群,在灰霾天气外出尽量戴上合适有效的口罩;居民应尽可能改善室内空气质量。     

Childhood exposure to PM10: relation between personal, classroom, and outdoor concentrations.

OBJECTIVES: To investigate the validity of outdoor concentrations of particulate matter < 10 microns diameter (PM10) as a measure of exposure in time series studies, and to study the extent to which differences between personal and outdoor PM10 concentrations can be explained. METHODS: Four to eight repeated measurements of personal and outdoor PM10 concentrations were conducted for 45 children, aged 10-12 years, from four schools in Wageningen and Amsterdam, The Netherlands. Repeated PM10 measurements in the classrooms were conducted in three of the schools. Averaging time was 24 hours for the personal and outdoor measurements, and eight hours (daytime) and 24 hours for the classroom measurements. For each child separately, personal exposures were related to outdoor concentrations in a regression analysis. The distribution of the individual correlation and regression coefficients was investigated. Information about factors that might influence personal exposures was obtained by questionnaire. RESULTS: Median Pearson's correlations between personal and outdoor concentrations were 0.63 for children with parents who did not smoke and 0.59 for children with parents who smoked. For children with parents who did not smoke, excluding days with exposure to environmental tobacco smoke (ETS) improved the correlation to a median R of 0.73. The mean personal PM10 concentration was 105 micrograms/m3; on average 67 micrograms/m3 higher than the corresponding outdoor concentrations. The main part of this difference could be attributed to exposure to ETS, to high PM10 concentrations in the classrooms, and to (indoor) physical activity. CONCLUSIONS: The results show a reasonably high correlation between repeated personal and outdoor PM10 measurements within children, providing support for the use of fixed site measurements as a measure of exposure to PM10 in epidemiological time series studies. The large differences between personal and outdoor PM10 concentrations probably result from a child's proximity to particle generating sources and particles resuspended by personal activities.     

Determinants of personal and indoor PM2.5 and absorbance among elderly subjects with coronary heart disease

Epidemiological studies have established an association between outdoor levels of fine particles (PM2.5) and cardiovascular health. However, there is little information on the determinants of PM2.5 exposures among persons with cardiovascular disease, a potentially susceptible population group. Daily outdoor, indoor and personal PM2.5 and absorbance (proxy for elemental carbon) concentrations were measured among elderly subjects with cardiovascular disease in Amsterdam, the Netherlands, and Helsinki, Finland, during the winter and spring of 1998-1999 within the framework of the ULTRA study. There were 37 non-smoking subjects in Amsterdam and 47 in Helsinki. In Amsterdam, where there were enough exposure events for analyses, exposure to environmental tobacco smoke (ETS) indoors was a major source of between-subject variation in PM2.5 exposures, and a strong determinant of PM2.5 and absorbance exposures. When the days with ETS were excluded, within-subject variation accounted for 89% of the total variation in personal PM2.5 and 97% in absorbance in Amsterdam. The respective figures were 66% and 61% in Helsinki. In both cities, outdoor levels of PM2.5 and absorbance were major determinants of personal and indoor levels. Traffic was also an important determinant of absorbance: living near a major street increased exposure by 22%, and every hour spent in a motor vehicle by 13% in Amsterdam. The respective increases were 37% and 9% in Helsinki. Cooking was associated with increased levels of both absorbance and PM2.5. Our results demonstrate that by using questionnaires in connection with outdoor measurements, exposure estimation of PM2.5 and its combustion originating fraction can be improved among elderly persons with compromised health.     

Evaluation of a real-time passive personal particle monitor in fixed site residential indoor and ambient measurements

Recent experimental findings in animals and humans indicate adverse respiratory effects from short-term exposures to particulate air pollutants, especially in sensitive subpopulations such as asthmatics. The relationship between air pollution and asthma has mainly been determined using particulate matter (PM) measurements from central sites. Validated tools are needed to assess exposures most relevant to health effects. Recently, a personal passive particulate sampler (personal Data-RAM, pDR, MIE Inc., Bedford, MA) has become available for studying personal exposures to PM with time resolution at 1 min. The pDR measures light scatter from PM in the 0.1-10 microM range, the significant range for health effects. In order to assess the ability of the pDR in predicting gravimetric mass, pDRs were collocated with PM2.5 and PM10 Harvard Impactors (HI) inside and outside nine homes of asthmatic children and at an outdoor central Air Pollution Control District site. Results are presented of comparisons between the HI samplers and the pDR in various modes of operation: passive, active, and active with a heated inlet. When used outdoors at fixed sites the pDR readings exhibit interference from high relative humidity (RH) unless operated with a method for drying inlet air such as a heater, or if readings at times of high RH are adjusted. The pDR correlates more highly with the HI PM2.5 than with the HI PM10 (r2 = 0.66 vs. 0.13 for outdoors, r2 = 0.42 vs. 0.20 for indoors). The pDR appears to be a useful tool for an epidemiologic study that aims to examine the relationship between health outcomes and personal exposure to peaks in PM.     

Polycyclic aromatic hydrocarbons bound to outdoor and indoor airborne particles (PM2.5) and their mutagenicity and carcinogenicity in Silesian kindergartens,Poland

Assessment of exposure to polycyclic aromatic hydrocarbons (PAHs) is important due to the widespread presence of PAHs in the environment and their toxicological relevance, especially to susceptible populations such as children and their health. The aim of this study is to compare indoor and outdoor concentrations of particulate matter with a diameter of 2.5 μm or less (PM2.5) and 15 individual PAHs, as well as contribution of the analyzed PAHs to mutagenic and carcinogenic activity. Samples were collected during spring season in two sites in southern Poland (Silesia) representing urban and rural areas. Indoor samples of PM2.5 were sampled in kindergartens. At the same time, in the vicinity of the kindergarten buildings, the collection of the outdoor PM2.5 samples was carried out. Mutagenic (MEQ) and carcinogenic (TEQ) equivalents related to BaP and the percentage share expressed as mutagenic (MP) and carcinogenic (CP) potential of each individual compound to the total mutagenic/carcinogenic potential of the PAH mixture were calculated. The obtained results show that high concentrations of PM2.5 (above 25 μg/m³) and 15 PM2.5-bound PAHs in outdoor and indoor air were similar in the two studied areas. In overall PAHs mutagenic and carcinogenic potential, the percentage share of benzo(a)pyrene (BaP) was dominant and varied from 49.0–54.5% to 62.5–70.0%, respectively. The carried out study indicates the necessity of reducing PAH emission from solid fuel combustion, which is reflected in PM2.5-bound PAHs concentrations and their diagnostic ratios. In the recent years, health effects on children resulting from their activity pattern and air quality in the public places have been a serious problem.     

Relationships among personal, indoor, and outdoor fine and coarse particle concentrations for individuals with COPD

This study characterizes the personal, indoor, and outdoor PM2.5, PM10, and PM2.5-10 exposures of 18 individuals with chronic obstructive pulmonary disease (COPD) living in Boston, MA. Monitoring was performed for each participant for six consecutive days in the winters of 1996 or 1997 and for six to twelve days in the summer of 1996. On each day, 12-h personal, indoor, and outdoor samples of PM2.5 and PM10 were collected simultaneously. Home characteristic information and time-activity patterns were also obtained. Personal exposures were higher than corresponding indoor and outdoor concentrations for all particle measures and for all seasons, except for winter indoor PM2.5-10 levels, which were higher than personal and outdoor levels. Higher personal exposures may be due to the proximity of the individuals to particle sources, such as cooking and cleaning. Indoor concentrations were associated with both outdoor concentrations and personal exposures (as determined by individual least square regression analyses), with associations strongest for PM2.5. Indoor PM2.5 concentrations were significantly associated with outdoor and personal levels for 12 and 15 of the 17 individuals, respectively. Both the strength and magnitude of the associations varied by individual. Also, personal PM2.5, but not PM2.5-10, exposures were associated with outdoor levels, with 10 of the 17 subjects having significant associations. The strength of the personal-outdoor association for PM2.5 was strongly related to that for indoor and outdoor levels, suggesting that home characteristics and indoor particulate sources were key determinants of the personal-outdoor association for PM2.5. Air exchange rates were found to be important determinants of both indoor and personal levels. Again, substantial interpersonal variability in the personal-outdoor relationship was found, as personal exposures varied by as much as 200% for a given outdoor level.     

Photometrically measured continuous personal PM(2.5) exposure: levels and correlation to a gravimetric method

There is evidence that hourly variations in exposure to airborne particulate matter (PM) may be associated with adverse health effects. Still there are only few published data on short-term levels of personal exposure to PM in community settings. The objectives of the study were to assess hourly and shorter-term variations in personal PM(2.5) exposure in Helsinki, Finland, and to compare results from portable photometers to simultaneously measured gravimetric concentrations. The effect of relative humidity on the photometric results was also evaluated. Personal PM(2.5) exposures of elderly persons were assessed for 24 h every second week, resulting in 308 successful measurements from 47 different subjects. Large changes in concentrations in minutes after cooking or changing microenvironment were seen. The median of daily 1-h maxima was over twice the median of 24-h averages. There was a strong significant association between the two means, which was not linear. Median (95th percentile) of the photometric 24-h concentrations was 12.1 (37.7) and of the 24-h gravimetric concentrations 9.2 (21.3) microg/m3. The correlation between the photometric and the gravimetric method was quite good (R2=0.86). Participants spent 94.1% of their time indoors or in a vehicle, where relative humidity is usually low and thus not likely to cause significant effects on photometric results. Even outdoors, the relative humidity had only modest effect on concentrations. Photometers are a promising method to explore the health effects of short-term variation in personal PM(2.5) exposure.     

Comparing gravimetric and real-time sampling of PM(2.5) concentrations inside truck cabins

As part of a study on truck drivers' exposure and health risk, pickup and delivery (P&D) truck drivers' on-road exposure patterns to PM(2.5) were assessed in five, weeklong sampling trips in metropolitan areas of five U.S. cities from April to August of 2006. Drivers were sampled with real-time (DustTrak) and gravimetric samplers to measure average in-cabin PM(2.5) concentrations and to compare their correspondence in moving trucks. In addition, GPS measurements of truck locations, meteorological data, and driver behavioral data were collected throughout the day to determine which factors influence the relationship between real-time and gravimetric samplers. Results indicate that the association between average real-time and gravimetric PM(2.5) measurements on moving trucks was fairly consistent (Spearman rank correlation of 0.63), with DustTrak measurements exceeding gravimetric measurements by approximately a factor of 2. This ratio differed significantly only between the industrial Midwest cities and the other three sampled cities scattered in the South and West. There was also limited evidence of an effect of truck age. Filter samples collected concurrently with DustTrak measurements can be used to calibrate average mass concentration responses for the DustTrak, allowing for real-time measurements to be integrated into longer-term studies of inter-city and intra-urban exposure patterns for truck drivers.     

Evaluation and quality control of personal nephelometers in indoor, outdoor and personal environments

Personal nephelometers provide useful real-time measurements of airborne particulate matter (PM). Recent studies have applied this tool to assess personal exposures and related health effects. However, a thorough quality control (QC) procedure for data collected from such a device in a large-scale exposure assessment study is lacking. We have evaluated the performance of a personal nephelometer (personal DataRAM or pDR) in the field. We present here a series of post hoc QC procedures for improving the quality of the pDR data. The correlations and the ratios between the pDRs and the collocated gravimetric measurements were used as indices of the pDR data quality. The pDR was operated in four modes: passive (no pump), active (with personal sampling pumps), active with a heated inlet, and a humidistat. The pDRs were worn by 21 asthmatic children, placed at their residences indoors and outdoors, as well as at a central site. All fixed-site pDRs were collocated with Harvard Impactors for PM2.5 (HI2.5). By examining the differences between the time-weighted average concentrations calculated from the real-time pDRs' readings and recorded internally by the pDRs, we identified 9.1% of the pDRs' measurements suffered from negative drifts. By comparing the pDRs' daily base level with the HI2.5 measurements, we identified 5.7% of the pDRs' measurements suffered from positive drifts. High relative humidity (RH) affected outdoor pDR measurements, even when a heater was used. Results from a series of chamber experiments suggest that the heated air stream cooled significantly after leaving the heater and entering the pDR light-scattering chamber. An RH correction equation was applied to the pDR measurements to remove the RH effect. The final R2 values between the fixed-site pDRs and the collocated HI2.5 measurements ranged between 0.53 and 0.72. We concluded that with a carefully developed QC procedure, personal nephelometers can provide high-quality data for assessing PM exposures on subjects and at fixed locations. We also recommend that outdoor pDRs be operated in the active mode without a heater and that the RH effect be corrected with an RH correction equation.     

A study of health effect estimates using competing methods to model personal exposures to ambient PM2.5

Various methods have been developed recently to estimate personal exposures to ambient particulate matter less than 2.5 microm in diameter (PM2.5) using fixed outdoor monitors as well as personal exposure monitors. One class of estimators involves extrapolating values using ambient-source components of PM2.5, such as sulfate and iron. A key step in extrapolating these values is to correct for differences in infiltration characteristics of the component used in extrapolation (such as sulfate within PM2.5) and PM2.5. When this is not done, resulting health effect estimates will be biased. Another class of approaches involves factor analysis methods such as positive matrix factorization (PMF). Using either an extrapolation or a factor analysis method in conjunction with regression calibration allows one to estimate the direct effects of ambient PM2.5 on health, eliminating bias caused by using fixed outdoor monitors and estimated personal ambient PM2.5 concentrations. Several forms of the extrapolation method are defined, including some new ones. Health effect estimates that result from the use of these methods are compared with those from an expanded PMF analysis using data collected from a health study of asthmatic children conducted in Denver, Colorado. Examining differences in health effect estimates among the various methods using a measure of lung function (forced expiratory volume in 1 s) as the health indicator demonstrated the importance of the correction factor(s) in the extrapolation methods and that PMF yielded results comparable with the extrapolation methods that incorporated correction factors.