Outdoor Particle Concentrations Research Articles

Experimental and Numerical Analysis of the Relationship Between Indoor and Outdoor Airborne Particles in an Operating Room

This work investigated the impact of the HVAC filtration system and indoor particle sources on the relationship between indoor and outdoor airborne particle size and concentrations in an operating room. Filters with efficiency between 65% and 99.97% were used in the investigation and indoor and outdoor particle size and concentrations were measured. A balance mass model was used for the simulation of the impact of the surgical team, deposition rate, HVAC exhaust and air change rates on indoor particle concentration. The experimental results showed that high efficiency filters would not be expected to decrease the risk associated with indoor particles larger than approximately 1 µm in size because normal filters are relatively efficient for these large particles. A good fraction of outdoor particles were removed by deposition on the HVAC system surfaces and this deposition increased with particle size. For particles of 0.3–0.5 µm in diameter, particle reduction was about 23%, while for particles >10 µm the loss was about 78%. The modelling results showed that depending on the type of filter used, the surgical team generated between 93% and 99% of total particles, while the outdoor air contributed only 1–6%.

Modeling, Measuring, and Characterizing Airborne Particles: Case Studies From Southwestern Luxembourg

The World Health Organization and the European Union highlight human exposure to air pollution, especially particulate matter as a priority environmental problem. Nevertheless, there are several problems related to the modeling of particulate matter in space and time as well as the chemical characterization of the involved particles. Previously used models are not applicable in all situations or particulate matter concentrations are often not detailed enough in respect to time resolution. Usually applied chemical methods to describe particulate matter composition are destructive and no information on surface composition can be obtained. Therefore, the authors’ main objective was the assessment of indoor and outdoor particle concentrations in southwestern Luxembourg applying state-of-the-art modeling approaches and measuring actual particulate matter concentrations with a high temporal resolution under various exposure scenarios. The spatial distribution of PM10 was modeled. Additional indoor particle measurements were carried out in a passenger car compartment and in an office building. Furthermore, chemical properties, assessed with a secondary ion mass spectrometer, show a complex mixture of elements on the surface of selected particles with distinct hot spots of potentially dangerous heavy metals.

Monitoring and control of particulate matter in indoor air: A review

The review discusses the sources and concentrations of particulate matter in different microenvironments, their effect on human health, monitoring and their possible control measures particularly in office and residential buildings. Effect of various ventilation strategies on particulate concentration in air has been discussed. The calculations suggest that if the outdoor particle concentration is not more than 5-10 times the indoor particle generation rate, ventilation could be a very effective tool to control the indoor particle concentration. For coarse particles the choice of ventilation strategy is not very crucial, but for fine particulate slow rate of ventilation is more effective.

Indoor and outdoor concentrations of fine particles, particle-bound PAHs and volatile organic compounds in Kaunas, Lithuania

This complex study presents indoor and outdoor levels of air-borne fine particles, particle-bound PAHs and VOCs at two urban locations in the city of Kaunas, Lithuania, and considers possible sources of pollution. Two sampling campaigns were performed in January-February and March-April 2009. The mean outdoor PM(2.5) concentration at Location 1 in winter was 34.5 ± 15.2 µg m(-3) while in spring it was 24.7 ± 12.2 µg m(-3); at Location 2 the corresponding values were 36.7 ± 21.7 and 22.4 ± 19.4 µg m(-3), respectively. In general there was little difference between the PM concentrations at Locations 1 and 2. PM(2.5) concentrations were lower during the spring sampling campaign. These PM concentrations were similar to those in many other European cities; however, the levels of most PAHs analysed were notably higher. The mean sum PAH concentrations at Locations 1 and 2 in the winter campaign were 75.1 ± 32.7 and 32.7 ± 11.8 ng m(-3), respectively. These differences are greater than expected from the difference in traffic intensity at the two sites, suggesting that there is another significant source of PAH emissions at Location 1 in addition to the traffic. The low observed indoor/outdoor (I/O) ratios indicate that PAH emissions at the locations studied arise primarily from outdoor sources. The buildings at both locations have old windows with wooden frames that are fairly permissive in terms of air circulation. VOC concentrations were mostly low and comparable to those reported from Sweden. The mean outdoor concentrations of VOC's were: 0.7 ± 0.2, 3.0 ± 0.8, 0.5 ± 0.2, 3.5 ± 0.3, and 0.2 ± 0.1 µg m(-3), for benzene, toluene, ethylbenzene, sum of m-, p-, o-xylenes, and naphthalene, respectively. Higher concentrations of VOCs were observed during the winter campaign, possibly due to slower dispersion, slower chemical transformations and/or the lengthy "cold start" period required by vehicles in the wintertime. A trajectory analysis showed that air masses coming from Eastern Europe carried significantly higher levels of PM(2.5) compared to masses from other regions, but the PAHs within the PM(2.5) are of local origin. It has been suggested that street dust, widely used for winter sanding activities in Eastern and Central European countries, may act not only as a source of PM, but also as source of particle-bound PAHs. Other potential sources include vehicle exhaust, domestic heating and long-range transport.

The Determinants of Mass Concentration of Indoor Particulate Matter in a Nursing Home

The study was conducted to evaluate the determinants of mass concentration of indoor particulate matter in a nursing home located in Taichung, Taiwan. PM2.5, PM10, temperature, relative humidity, CO, CO2, O3 and colony counts were collected in 2 bedrooms and their adjacent outdoor environments from November 2009 to January 2010. The results of multiple regression analysis suggested that the explanatory variables which included outdoor particle concentrations, indoor occupancy, different types of activities and ventilation accounted for 40.9% and 63.4% of the variance in the indoor PM2.5 concentration in Room A which is close to neighboring buildings and Room B which is close to main traffic, respectively. The explanatory variables accounted for 49.1% and 85.5% of the variance in the indoor PM10 concentration in Room A and B, respectively. Moreover, the result of correlation analysis showed that both indoor PM2.5 and PM10 concentrations were correlated to temperature, relative humidity and CO.

Fine Particulate Matter Measurements in Swiss Hospitality Venues: What Is the Effect of Spatial Separation Between Smoking and Non-smoking Areas?

ISEE-0214 Background and Objective: Worldwide, a variety of non-smoking policies have been implemented for public places. In Switzerland, four different smoking regulations can be encountered in hospitality venues within a relatively small geographic area: i) complete smoking bans, ii) designating of smoking and non-smoking areas in the same room, iii) separating smoking and non-smoking rooms, and iv) no restrictions. The impact of such regulations on ETS exposure levels is still unclear. Methods: We performed 124 measurements of particulate matter (PM2.5) in 95 hospitality venues. We compared PM2.5 concentrations between venues with different smoking regulations, taking relevant characteristics of the venue into account, such as the type of ventilation, the presence of additional PM2.5 sources and outdoor fine particle concentration. In particular, we evaluated the effect of different types of spatial separation between smoking and non-smoking areas within the same venue on PM2.5 levels. Results: In non-smoking venues with a complete smoking ban, the geometric mean PM2.5 level was 20.4 μg/m3. In venues with smoking restrictions, geometric mean PM2.5 levels were 56.5 μg/m3 in non-smoking areas and 119.0 μg/m3 in smoking areas. In venues without smoking restrictions mean PM2.5 concentration was 98.5 μg/m3. PM2.5 levels in non-smoking areas that were located in the same room as smoking-areas were 75.6 μg/m3. Even if the non-smoking areas were spatially separated into two rooms in the same venue, geometric mean PM2.5 levels were still considerably increased compared to entirely smoke-free venues (52.2 μg/m3 vs. 20.4 μg/m3). Conclusions: Significantly increased PM2.5 levels were found in non-smoking areas if smoking was allowed anywhere in the venue. This study shows that spatial separation of smoking room does not effectively protect non-smoking areas from ETS.

Particulate Matter Mass Concentration (PM10) under Different Ventilation Methods in Classrooms

Recently, studies have shown that the classroom environment is very important for students’ health and performance. Thus, the evaluation of indoor air quality (IAQ) in a classroom is necessary to ensure students’ well-being. In this paper the emphasis is on airborne concentration of particulate matter (PM) in adult education rooms. The mass concentration of PM10 particulates was measured in two classrooms under different ventilation methods in the University of Reading, UK, during the winter period of 2008. In another study the measurement of the concentration of particles was accompanied with measurements of CO2 concentration in these classrooms but this study is the subject of another publication. The ambient PM10, temperature, relative humidity, wind speed and direction, and rainfall events were monitored as well. In general, this study showed that outdoor particle concentrations and outdoor meteorological parameters were identified as significant factors influencing indoor particle concentration levels. Ventilation methods showed significant effects on air change rate and on indoor/outdoor (I/O) concentration ratios. Higher levels of indoor particulates were seen during occupancy periods. I/O ratios were significantly higher when classrooms were occupied than when they were unoccupied, indicating the effect of both people presence and outdoor particle concentration levels. The concentrations of PM10 indoors and outdoors did not meet the requirements of WHO standards for PM10 annual average.

Prediction of the concentration and diameter distribution of indoor suspended particulate matter

PurposeThe purpose of this paper is to establish mass balance model and predict the concentration and diameter distribution of indoor suspended particulate matters (SPM).Design/methodology/approachTaking the small offices and residences for a research objective, this paper analyzes the major factors to affect the concentration and diameter distribution of indoor SPM, founds the deposition ratio model, the penetration factor model and the mass balance model to predict the concentration and diameter distribution of indoor SPM. According to the real‐time measuring data, the feature of building defence structure and the concentration and diameter distribution of outdoor SPM, the deposition model, the penetration model and indoor air capacity are used as input parameter of the mass balance model.FindingsThe size of defence in natural ventilation, the pressure difference of both sides and the friction velocity have less influence on the concentration and diameter distribution of indoor SPM, but the concentration and diameter distribution of outdoor SPM mainly affects that of indoor SPM. Indoor particle concentration change with outdoor particle concentration, and less than later because of indoor particle deposition. The prediction results are basically in agreement with the measuring data.Research limitations/implicationsReal‐time and accuracy of measuring data of outdoor SPM are the main limitations which the prediction model are simulated.Practical implicationsThe prediction results can provide scientific theory basis for making environmental standards of particulate matter and the control of indoor air quality.Originality/valueA new method to predict the concentration and diameter distribution of indoor SPM.

Hourly variation in fine particle exposure is associated with transiently increased risk of ST segment depression

Objectives: To evaluate whether hourly changes in fine particle (PM2.5, diameter<2.5 µm) exposure or outdoor particle concentrations are associated with rapid ischaemic responses. Methods: 41 non-smoking elderly people with coronary...

PROBE-PM: A new way to simulate particle transport in ventilation systems

A ventilation system usually runs on a certain schedule. The boundary conditions, such as the time-dependent outdoor particle concentrations and indoor particle generating sources, vary dynamically. Ventilated rooms are connected to ventilation ducts and filters, and indoor particle concentration and particle deposition on duct surfaces are interdependent. Thus it is important to study particle transport in the entire ventilation system and take the dynamic characteristics into account to assess particle pollution in the entire system more accurately. A generalized model is proposed in this study to estimate particle concentration throughout an entire ventilation system as well as mass loading of particles on ventilation components. Model equations describe particle movement in different ventilation components, including filters, ducts, and rooms. Penetration factors are adopted for filters and ducts, and particle concentrations in rooms are calculated by a lumped parameter method. This generalized model can be applied to any ventilation system, and a new software, PROBE-PM, was developed based on the presented model. Four case studies are carried out using this new software to demonstrate the application of the model.

Indoor/outdoor relationships of size-resolved particle concentrations in naturally ventilated school environments

Assessment of indoor air quality in typical classrooms is vital to students’ health and their performance. The present study was designed to monitor indoor and outdoor size-resolved particle concentrations in a naturally ventilated classroom and investigate factors influencing their levels and relationships. The experiments were performed, at normal ventilation condition with doors and windows opened, on the top floor of a public school building near a busy commercial area of Chiang Mai, Thailand. The particle number concentrations were measured using an optical counter with four size intervals between 0.3 and 5.0 μm. The dataset was collected during weekdays and weekends with a 24 h sampling period over November and December 2005. It was observed that the median indoor particle number concentrations during daytime for 0.3–0.5, 0.5–1.0, 1.0–2.5, and 2.5–5.0 μm size intervals were about 1.6×10 8, 1.7×10 7, 1.2×10 6, and 4.1×10 5 particles/m 3, respectively. It was also found that concentrations at weekends were slightly higher those measured on weekdays, and at night, appeared to be higher than daytime. Indoor particles were observed to exhibit similar temporal variation pattern with outdoor particles. Results suggested that a significant contribution to indoor particles was from penetration of outdoor particles, whereas indoor sources generated from occupant activity did not show strong evidence. High outdoor particle loading and high air exchange rate were thought to be predominant causes. Ratios of indoor-to-outdoor (I/O) particle concentrations varied in a relatively narrow range from 0.69 to 0.88 with average values well below 1. The I/O ratios were in the range from 0.74 to 0.88 for submicrometer particles and from 0.69 to 0.80 for supermicrometer particles.

Ambient site, home outdoor and home indoor particulate concentrations as proxies of personal exposures

Despite strong longitudinal associations between particle personal exposures and ambient concentrations, previous studies have found considerable inter-personal variability in these associations. Factors contributing to this inter-personal variability are important to identify in order to improve our ability to assess particulate exposures for individuals. This paper examines whether ambient, home outdoor and home indoor particle concentrations can be used as proxies of corresponding personal exposures. We explore the strength of the associations between personal, home indoor, home outdoor and central outdoor monitoring site ("ambient site") concentrations of sulfate, fine particle mass (PM(2.5)) and elemental carbon (EC) by season and subject for 25 individuals living in the Boston, MA, USA area. Ambient sulfate concentrations accounted for approximately 70 to 80% of the variability in personal and indoor sulfate levels. Correlations between ambient and personal sulfate, however, varied by subject (0.1-1.0), with associations between personal and outdoor sulfate concentrations generally mirroring personal-ambient associations (median subject-specific correlations of 0.8 to 0.9). Ambient sulfate concentrations are good indicators of personal exposures for individuals living in the Boston area, even though their levels may differ from actual personal exposures. The strong associations for sulfate indicate that ambient concentrations and housing characteristics are the driving factors determining personal sulfate exposures. Ambient PM(2.5) and EC concentrations were more weakly associated with corresponding personal and indoor levels, as compared to sulfate. For EC and PM(2.5), local traffic, indoor sources and/or personal activities can significantly weaken associations with ambient concentrations. Infiltration was shown to impact the ability of ambient concentrations to reflect exposures with higher exposures to particles from ambient sources during summer. In contrast in the winter, lower infiltration can result in a greater contribution of indoor sources to PM(2.5) and EC exposures. Placing EC monitors closer to participants' homes may reduce exposure error in epidemiological studies of traffic-related particles, but this reduction in exposure error may be greater in winter than summer. It should be noted that approximately 20% of the EC data were below the field limit of detection, making it difficult to determine if the weaker associations with the central site for EC were merely a result of methodological limitations.

Dependence of Home Outdoor Particulate Mass and Number Concentrations on Residential and Traffic Features in Urban Areas

The associations between residential outdoor and ambient particle mass, fine particle absorbance, particle number (PN) concentrations, and residential and traffic determinants were investigated in four European urban areas (Helsinki, Athens, Amsterdam, and Birmingham). A total of 152 nonsmoking participants with respiratory diseases, not exposed to occupational pollution, were included in the study, which comprised a 7-day intensive exposure monitoring period of both indoor and home outdoor particle mass and number concentrations. The same pollutants were also continuously measured at ambient fixed sites centrally located to the studied areas (fixed ambient sites). Relationships between concentrations measured directly outside the homes (residential outdoor) and at the fixed ambient sites were pollutant-specific, with substantial variations among the urban areas. Differences were more pronounced for coarse particles due to resuspension of road dust and PN, which is strongly related to traffic emissions. Less significant outdoor-to-fixed variation for particle mass was observed for Amsterdam and Birmingham, predominantly due to regional secondary aerosol. On the contrary, a strong spatial variation was observed for Athens and to a lesser extent for Helsinki. This was attributed to the overwhelming and time-varied inputs from traffic and other local sources. The location of the residence and traffic volume and distance to street and traffic light were important determinants of residential outdoor particle concentrations. On average, particle mass levels in suburban areas were less than 30% of those measured for residences located in the city center. Residences located less than 10 m from a street experienced 133% higher PN concentrations than residences located further away. Overall, the findings of this multi-city study, indicated that (1) spatial variation was larger for PN than for fine particulate matter (PM) mass and varied between the cities, (2) vehicular emissions in the residential street and location in the center of the city were significant predictors of spatial variation, and (3) the impact of traffic and location in the city was much larger for PN than for fine particle mass.

Relationship between indoor, outdoor, and personal fine particle concentrations for individuals with COPD and predictors of indoor-outdoor ratio in Mexico city

Personal exposure and indoor and outdoor exposure to PM(10) and PM(2.5) of 38 individuals with chronic obstructive pulmonary disease (COPD) was characterized from February through November 2000. All participants lived in Mexico City and were selected based on their area of residence southeast (n=15), downtown (n=15), and southwest (n=8). Participants were monitored at home using personal PM(2.5) monitoring devices. Indoor and outdoor levels of PM(10) and PM(2.5) were measured using MiniVol samplers. Concurrent individual exposure measurements, indoor and outdoor levels of PM(2.5), which averaged 38.4 (SD 21.4), 30.6 (SD 15.8), and 30.5 mug/m(3) (SD 19.4), respectively. Indoor PM(2.5) concentrations explained 40% of the variability of personal exposure. In addition, the factors that most affected personal exposure were regular indoor contact with animals, mold, cooking activities, and aerosol use, indicating that internal sources may largely affect individual exposure.

Associations of Fine and Ultrafine Particulate Air Pollution With Stroke Mortality in an Area of Low Air Pollution Levels

Daily variation in outdoor concentrations of inhalable particles (PM(10) <10 microm in diameter) has been associated with fatal and nonfatal stroke. Toxicological and epidemiological studies suggest that smaller, combustion-related particles are especially harmful. We therefore evaluated the effects of several particle measures including, for the first time to our knowledge, ultrafine particles (<0.1 microm) on stroke. Levels of particulate and gaseous air pollution were measured in 1998 to 2004 at central outdoor monitoring sites in Helsinki. Associations between daily levels of air pollutants and deaths caused by stroke among persons aged 65 years or older were evaluated in warm and cold seasons using Poisson regression. There was a total of 1304 and 1961 deaths from stroke in warm and cold seasons, respectively. During the warm season, there were positive associations of stroke mortality with current- and previous-day levels of fine particles (<2.5 microm, PM(2.5)) (6.9%; 95% CI, 0.8% to 13.8%; and 7.4%; 95% CI, 1.3% to 13.8% for an interquartile increase in PM(2.5)) and previous-day levels of ultrafine particles (8.5%; 95% CI, -1.2% to 19.1%) and carbon monoxide (8.3; 95% CI, 0.6 to 16.6). Associations for fine particles were mostly independent of other pollutants. There were no associations in the cold season. Our results suggest that especially PM(2.5), but also ultrafine particles and carbon monoxide, are associated with increased risk of fatal stroke, but only during the warm season. The effect of season might be attributable to seasonal differences in exposure or air pollution mixture.

The effects of ozone/limonene reactions on indoor secondary organic aerosols

An indoor air quality model was used to predict dynamic particle mass concentrations based on homogeneous chemical mechanisms and partitioning of semi-volatile products to particles. The ozone–limonene reaction mechanism was combined with gas-phase chemistry of common atmospheric organic and inorganic compounds and incorporated into the indoor air quality model. Experiments were conducted in an environmental chamber to investigate secondary particle formation resulting from ozone/limonene reactions. Experimental results indicate that significant fine particle growth occurs due to the interaction of ozone and limonene and subsequent intermediate by-products. Secondary particle mass concentrations were estimated from the measured particle size distribution. Predicted particle mass concentrations were in good agreement with experimental results—generally within ∼25% at steady-state conditions. Both experimental and predicted results suggest that air exchange rate plays a significant role in determining secondary fine particle levels in indoor environments. Secondary particle mass concentrations are predicted to increase substantially with lower air exchange rates, an interesting result given a continuing trend toward more energy efficient buildings. Lower air exchange rates also shifted the particle size distribution toward larger particle diameters. Secondary particle mass concentrations are also predicted to increase with higher outdoor ozone concentrations, higher outdoor particle concentrations, higher indoor limonene emission rates, and lower indoor temperatures.

Relative levels of indoor and outdoor particle number concentrations in a residential building in Xi'an

The time series of indoor and outdoor particle number concentrations in a naturally ventilated residential building in Xi'an were tested simultaneously for 7 days in summer. The relationships between indoor and outdoor concentrations were examined and discussed, and linear regression analysis was employed to correlate the indoor and outdoor concentrations. The diurnal cycles of indoor and outdoor particle concentrations of different particle size ranges all showed positive correlations between indoor and outdoor number concentrations. The I/O ratios of number concentrations varied with the increase of particle size in the range of 0.89 (±0.19) to 0.99 (±0.15).

Indoor and outdoor submicrometer particles: Exposure and epidemiologic relevance (“the 3 indoor Ls”)

Airborne particles represent a very important pollutant with respect to healthy housing conditions. The snag is that in lack of indoor data epidemiological studies focusing on submicron and ultrafine (<100 nm in diameter) particles are usually forced to use outdoor particle concentrations only. On the other hand it is known that people spend most of their time indoors. The aim of this paper is therefore to give a short comprehensive overview of the indoor/outdoor problem with regard to submicron and ultrafine particles, investigating how indoor particle size distributions correlate with outdoor concentrations in the absence of significant indoor sources. In the absence of a major indoor source, total indoor particle number concentrations were always lower than outdoor concentrations. The highest ratios between indoor and outdoor concentrations tend to correlate with lower rather than higher total outdoor particle number concentrations. Concentration ratios depend on particle size. Time lags of the correlation coefficients between the concentrations of indoor and outdoor particles of different diameters have been determined to assess the time the particles need to enter the indoor site through closed modern-type windows. Typical lag times of 0.5-3 h between somewhat smaller indoor particles and somewhat larger outdoor particles have been observed. To assess the resulting particle burden for humans, a suitably weighted average emphasizing indoor aerosol particles must be used. To classify the health effects of particles of different diameters, different decreases of particle number concentrations depending on the particle sizes must be taken into account if indoor concentrations cannot be measured and outdoor concentrations are used in place of indoor measurements. In urban areas, ultrafine particles originate primarily from rapidly increasing traffic, which is the dominating source at many urban sites. The influence of traffic on outdoor and indoor concentrations is therefore of special interest.

Childrenʼs Exposure to Diesel Exhaust at a Rural Elementary School

SAB5-O-04 Diesel exhaust has been associated with health effects in humans, including respiratory illness and cancer. Children are of particular concern regarding diesel exposure from schools buses because their lungs are still developing and they can be more susceptible to health effects than adults. In this study, a direct exposure assessment was conducted at the elementary school in Potsdam, NY in late October 2005 for 5 days and early February 2006 for 4 days. Sampling was performed for 2 hours in the morning and 2 hours in the afternoon corresponding with the school bus dropoff and pickup times. Matched indoor/outdoor semi-continuous instruments were used to measure ultrafine particle (UFP) counts, particle-bound PAHs, and particle size distribution. One indoor and several outdoor integrated filter samplers collected PM2.5 mass on both quartz and Teflon filters. The filter samples were analyzed for mass and organic and elemental carbon (OC/EC). The highest PM2.5 concentrations were found indoors and the outdoor concentrations in the bus pickup and dropoff area were found to be slightly higher than those from the upwind site. All outdoor PM2.5 concentrations were below 12 μg/m3. The elemental carbon measurements were found to be below the detection limit during the fall field intensive, which is likely due to the fact that the buses shut off immediately upon arrival at the school, reducing the source strength, and the sampling period was short. The sampling period was increased from 4 hours to 8 hours for the winter field intensive. Time-series data from the semi-continuous instruments showed clear increases in UFP number concentration to more than 100,000 particles/cm3 during the times that the buses arrived and departed from the school compared with less than 10,000 particles/cm3 before the buses arrived. A strong correlation between the indoor air and the outdoor particle concentrations was found, and the penetration of the outdoor particles indoors was found to be almost 100%. The results of this study illustrate that the bus pickup and dropoff next to the elementary school results in a short-term, high concentration exposures to UFP both outside and inside the school.

Continuous weeklong measurements of personal exposures and indoor concentrations of fine particles for 37 health-impaired North Carolina residents for up to four seasons

A study of personal exposures and indoor and outdoor concentrations of particles was carried out in 2000–2001 for 37 health-impaired residents of North Carolina. Earlier papers have dealt with the 24-h integrated gravimetric samples; this report adds the continuous data (1-min resolution) using optical scattering devices (personal data RAMs, or pDRs) for personal and indoor measurements. Subjects and their households were sampled for 7 consecutive days in each of four seasons, although not all subjects completed all four seasons. Each subject completed an activity diary with 15-min resolution on each day giving his or her presence in one of six locations and describing activities with the potential for increased exposure to particles. More than 800 person-days and 1.1×10 6 person-min of valid personal exposures and indoor air concentrations were collected. The pDRs compared well with the PM 2.5 gravimetric devices, with an R 2 of 87% compared to the indoor Harvard impactor (HI), and 70% compared to the personal exposure monitor (PEM). As found in previous studies, (and as expected due to the calibration of these devices with an aerosol of higher density than normal ambient and indoor aerosols), the pDRs overestimated the gravimetric concentrations by 20–50%. Because the correction factor varied by season and by type of sample (indoor vs. personal), no overall correction factor could be applied. The estimated mean increases in exposure during three common activities (cooking, cleaning, and personal care) were 56, 28, and 20 μg m −3, respectively. Several less common activities, such as burning food and using a fireplace were found to result occasionally in very high (>1500 μg m −3) short-term peaks of exposure. Although households with smoking were ineligible for participation, two households did have significant smoking, and had the highest average personal exposures and indoor concentrations of all the study homes. The diurnal variation of personal exposures and indoor concentrations was bimodal, with peaks occurring between 10 and 11 AM and 5 and 6 PM. The “damping effect” of the home due to air exchange caused the infiltrated outdoor particles to show only a unimodal variation, with a single broad and mild peak occurring between 6 and 10 AM. A method for identifying peak concentrations due to indoor sources and personal activities was developed. Peaks due to personal activities and indoor sources occurred about 23% and 14% of the time, respectively. On average, outdoor particles contributed about half of the total personal exposures and indoor concentrations, but there was wide variation across subjects. These findings using the MIE data were then compared to previously published estimates using measurements of sulfur from the gravimetric data; good agreement ( R 2 values from 50% to 65%) was found, providing a measure of validation to both methods. Personal exposures exceeded co-located indoor concentrations by 2–3 μg m −3, confirming findings of a small but statistically significant “personal cloud” for PM 2.5 made in previous studies using gravimetric 24-h integrating monitors.