A comparative study of walking-induced dust resuspension using a consistent test mechanism.

UNLABELLED: Human walking influences indoor air quality mainly by resuspending dust particles settled on the floor. This study characterized walking-induced particle resuspension as a function of flooring type, relative humidity (RH), surface dust loading, and particle size using a consistent resuspension mechanism. Five types of flooring, including hardwood, vinyl, high-density cut pile carpet, low-density cut pile carpet, and high-density loop carpet, were tested with two levels of RH (40% and 70%) and surface dust loading (2 and 8 g/m(2) ), respectively. Resuspension fraction ra (fraction of surface dust resuspended per step) for house dust was found to be varied from 10(-7) to 10(-4) (particle size: 0.4-10 µm). Results showed that for particles at 0.4-3.0 µm, the difference in resuspension fraction between carpets and hard floorings was not significant. For particles at 3.0-10.0 µm, carpets exhibited higher resuspension fractions compared with hard floorings. Increased RH level enhanced resuspension on high-density cut pile carpet, whereas the opposite effect was observed on hard floorings. Higher surface dust loading was associated with lower resuspension fractions on carpets, while on hard floorings the effect of surface dust loading varied with different RH levels. PRACTICAL IMPLICATIONS: The results from this study validate the recommendation that people sensitive to allergens could select hard floorings to reduce exposure and related adverse health outcomes. The results can also be applied to exposure models to determine the overall impact of exposure to resuspension as compared with other particle sources.

PM2.5 and ultrafine particles emitted during heating of commercial cooking oils.

UNLABELLED: Seven commercial cooking oils were investigated to determine the PM(2.5) mass and ultrafine particle (UFP) emission rates and emission fluxes (rates per area). The results of this study showed that at 197°C soybean, safflower, canola, and peanut oils produced lower PM(2.5) emission fluxes (6.1 × 10(5), 3.0 × 10(5), 5.4 × 10(5), and 3.9 × 10(5) µg/min/m(2), respectively) than corn, coconut, and olive oils (2.7 × 10(6), 2.9 × 10(6), and 5.7 × 10(6) µg/min/m(2), respectively). Similarly, the total particle number flux at 197°C was lower for soybean, safflower, and canola oils (3.5 × 10(13), 8.6 × 10(13), and 1.0 × 10(14) #/min/m(2), respectively) than the corn, coconut, olive, and peanut oils (2.4 × 10(14), 1.4 × 10(14), 1.7 × 10(14), and 3.8 × 10(14) #/min/m(2), respectively). In general, oils with a higher smoke temperature resulted in lower particle concentrations over the measured temperature range (131-197°C). The percentage of UFP (particle diameter D(p) 10-100 nm) to total particles (D(p) 10-500 nm) ranged from 76 to 99% for this temperature range. Particles below 10 nm in diameter were not measured. The particle number size distribution showed a polydisperse behavior with major mode sizes ranging from 25 nm (for peanut oil) to 82 nm (for soybean oil) at an oil temperature of 197°C. PRACTICAL IMPLICATIONS: The study presents particle number and mass concentrations, size distributions, emission rates, and emission fluxes from heating common cooking oils. The emission rates and emission fluxes can be used as inputs to models for indirect exposure analysis studies. The study may also be used to provide guidance on choosing oils that result in lower emission rates when heated.

Relationships of outdoor and indoor ultrafine particles at residences downwind of a major international border crossing in Buffalo, NY.

UNLABELLED: During winter 2006, indoor and outdoor ultrafine particle (UFP) size distribution measurements for particles with diameters from 5.6 to 165 nm were taken at five homes in a neighborhood directly adjacent to the Peace Bridge Complex (PBC), a major international border crossing connecting Buffalo, New York to Fort Erie, Ontario. Monitoring with 1-s time resolution was conducted for several hours at each home. Participants were instructed to keep all external windows and doors closed and to refrain from cooking, smoking, or other activity that may result in elevating the indoor UFP number concentration. Although the construction and age for the homes were similar, indoor-to-outdoor comparisons indicate that particle infiltration rates varied substantially. Overall, particle concentrations indoors were lower and less variable than particle concentrations outdoors, with average indoor-outdoor ratios ranging from 0.1 to 0.5 (mean 0.34) for particles between 5.6 and 165 nm in diameter. With no indoor sources, the average indoor-outdoor ratios were lowest (0.2) for 20-nm particles, higher (0.3) for particles <10 nm, and highest (0.5) for particles 70-165 nm. PRACTICAL IMPLICATIONS: This study provides insight into the penetration of UFP into homes and the resulting change in particle size distributions as particles move indoors near a major diesel traffic source. Although people spend most of their time in their homes, exposure estimates for epidemiological studies are generally determined using ambient concentrations. The findings of this study will contribute to improved size-resolved UFP exposure estimates for near roadway exposure assessments and epidemiological studies.

Investigations of the proximity effect for pollutants in the indoor environment.

More than a dozen indoor air quality studies have reported a large discrepancy between concentrations measured by stationary indoor monitors (SIMs) and personal exposure monitors (PEMs). One possible cause of this discrepancy is a source proximity effect, in which pollutant sources close to the respondent cause elevated and highly variable exposures. This paper describes three sets of experiments in a home using real-time measurements to characterize and quantify the proximity effect relative to a fixed distant location analogous to a SIM. In the first set of experiments, using sulfur hexafluoride (SF6) as a continuously emitting tracer pollutant from a point source, measurements of pollutant concentrations were made at different distances from the source under different air exchange rates and source strengths. A second set of experiments used a continuous point source of carbon monoxide (CO) tracer pollutant and an array of high time resolution monitors to collect simultaneous concentration readings at different locations in the room. A third set of experiments measured particle count density and particle-bound polycyclic aromatic hydrocarbon (PAH) concentrations emitted from a continuous particle point source (an incense stick) using two particle counters and two PAH monitors, and included human activity periods both before and during the source emission period. Results from the SF6 and CO experiments show that while the source is emitting, a source proximity effect can be seen in the increases in the mean and median and in the variability of concentrations closest to the source, even at a distance of 2.0 m from the source under certain settings of air exchange rate and source strength. CO concentrations at locations near the source were found to be higher and more variable than the predictions of the mass balance model. For particles emitted from the incense source, a source proximity effect was evident for the fine particle sizes (0.3 to 2.5 microm) and particle-bound PAH up to at least 1.0 m from the source. Analysis of spatial and temporal patterns in the data for the three tracer pollutants reveal marked transient elevations of concentrations as seen by the monitor, referred to as "microplumes," particularly at locations close to the source. Mixing patterns in the room show complex patterns and directional effects, as evidenced by the variable intensity of the microplume activity at different locations. By characterizing the spatial and temporal variability of pollutant concentrations in the home, the proximity effect can be quantified, leading to improved indoor monitoring designs and models of human exposure to air pollutants.