Sample integrity evaluation and EPA method 325B interlaboratory comparison for select volatile organic compounds collected diffusively on Carbopack X sorbent tubes.

A sample integrity evaluation and an interlaboratory comparison were conducted in application of U.S. Environmental Protection Agency (EPA) Methods 325A and 325B for diffusively monitoring benzene and other selected volatile organic compounds (VOCs) using Carbopack X sorbent tubes. To evaluate sample integrity, VOC samples were refrigerated for up to 240 days and analyzed using thermal desorption/gas chromatography-mass spectrometry at the EPA Office of Research and Development laboratory in Research Triangle Park, NC, USA. For the interlaboratory comparison, three commercial analytical laboratories were asked to follow Method 325B when analyzing samples of VOCs that were collected in field and laboratory settings for EPA studies. Overall results indicate that the selected VOCs collected diffusively on sorbent tubes generally were stable for 6 months or longer when samples were refrigerated. This suggests the specified maximum 30-day storage time of VOCs collected diffusively on Carbopack X passive samplers and analyzed using Method 325B might be able to be relaxed. Interlaboratory comparison results were in agreement for the challenge samples collected diffusively in an exposure chamber in the laboratory, with most measurements within ±25% of the theoretical concentration. Statistically significant differences among laboratories for ambient challenge samples were small, less than 1 part per billion by volume (ppbv). Results from all laboratories exhibited good precision and generally agreed well with each other.

Overview of the Brooklyn traffic real-time ambient pollutant penetration and environmental dispersion (B-TRAPPED) study: theoretical background and model for design of field experiments.

The Brooklyn traffic real-time ambient pollutant penetration and environmental dispersion (B-TRAPPED) study was a multidisciplinary field research project that investigated the transport, dispersion, and infiltration processes of traffic emission particulate matter (PM) pollutants in a near-highway urban residential area. The urban PM transport, dispersion, and infiltration processes were described mathematically in a theoretical model that was constructed to develop the experimental objectives of the B-TRAPPED study. In the study, simultaneous and continuous time-series PM concentration and meteorological data collected at multiple outdoor and indoor monitoring locations were used to characterize both temporal and spatial patterns of the PM concentration movements within microscale distances (<500 m) from the highway. Objectives of the study included (1) characterizing the temporal and spatial PM concentration fluctuation and distribution patterns in the urban street canyon; (2) investigating the effects of urban structures such as a tall building or an intersection on the transport and dispersion of PM; (3) studying the influence of meteorological variables on the transport, dispersion, and infiltration processes; (4) characterizing the relationships between the building parameters and the infiltration mechanisms; (5) establishing a cause-and-effect relationship between outdoor-released PM and indoor PM concentrations and identifying the dominant mechanisms involved in the infiltration process; (6) evaluating the effectiveness of a shelter-in-place area for protection against outdoor-released PM pollutants; and (7) understanding the predominant airflow and pollutant dispersion patterns within the neighborhood using wind tunnel and CFD simulations. The 10 papers in this first set of papers presenting the results from the B-TRAPPED study address these objectives. This paper describes the theoretical background and models representing the interrelated processes of transport, dispersion, and infiltration. The theoretical solution for the relationship between the time-dependent indoor PM concentration and the initial PM concentration at the outdoor source was obtained. The theoretical models and solutions helped us to identify important parameters in the processes of transport, dispersion, and infiltration. The B-TRAPPED study field experiments were then designed to investigate these parameters in the hope of better understanding urban PM pollutant behaviors.

Characterization of traffic-related PM concentration distribution and fluctuation patterns in near-highway urban residential street canyons.

Analyses of outdoor traffic-related particulate matter (PM) concentration distribution and fluctuation patterns in urban street canyons within a microscale distance of less than 500 m from a highway source are presented as part of the results from the Brooklyn Traffic Real-Time Ambient Pollutant Penetration and Environmental Dispersion (B-TRAPPED) study. Various patterns of spatial and temporal changes in the street canyon PM concentrations were investigated using time-series data of real-time PM concentrations measured during multiple monitoring periods. Concurrent time-series data of local street canyon wind conditions and wind data from the John F. Kennedy (JFK) International Airport National Weather Service (NWS) were used to characterize the effects of various wind conditions on the behavior of street canyon PM concentrations.Our results suggest that wind direction may strongly influence time-averaged mean PM concentration distribution patterns in near-highway urban street canyons. The rooftop-level wind speeds were found to be strongly correlated with the PM concentration fluctuation intensities in the middle sections of the street blocks. The ambient turbulence generated by shifting local wind directions (angles) showed a good correlation with the PM concentration fluctuation intensities along the entire distance of the first and second street blocks only when the wind angle standard deviations were larger than 30 degrees. Within-canyon turbulent shearing, caused by fluctuating local street canyon wind speeds, showed no correlation with PM concentration fluctuation intensities. The time-averaged mean PM concentration distribution along the longitudinal distances of the street blocks when wind direction was mostly constantly parallel to the street was found to be similar to the distribution pattern for the entire monitoring period when wind direction fluctuated wildly. Finally, we showed that two different PM concentration metrics-time-averaged mean concentration and number of concentration peaks above a certain threshold level-can possibly lead to different assessments of spatial concentration distribution patterns.

Parameterization of meteorological variables in the process of infiltration of outdoor ultrafine particles into a residential building.

As part of the Brooklyn Traffic Real-Time Ambient Pollutant Penetration and Environmental Dispersion (B-TRAPPED) study, a field investigation was conducted of the mechanisms involved in infiltration of outdoor particles (0.02 microm to 1 microm) into a near-highway urban residential building. Using continuous real-time total number concentration time-series data measured simultaneously at multiple outdoor and indoor locations, the infiltration time was estimated for various indoor sites by using the cross-correlation analysis method. The effects of meteorological variables on infiltration times were also characterized at given locations. In particular, infiltration time was examined as a function of outdoor mean rooftop wind speed. Outdoor and indoor temperature and relative humidity were also investigated in relation to infiltration times. Our results showed that outdoor wind speed was the dominant meteorological parameter affecting the infiltration rate, but no correlation was found with temperature. The outdoor-indoor PM concentration ratio was found to be significantly different for the first and second floors of the test building. Finally, we determined the effectiveness of a protective shelter-in-place area inside the building by calculating infiltration times into the area. We found that the shelter-in-place area offered some protection against the infiltrating particles because of increased attenuation of the outdoor concentration.

Building characterization and aerosol infiltration into a naturally ventilated three-story apartment building.

Understanding infiltration of outdoor pollutants was an integral part of the Brooklyn Traffic Real-Time Ambient Pollutant Penetration and Environmental Dispersion (B-TRAPPED) study. For this reason, the structural and air exchange properties of the three-story row house in Brooklyn, NY, USA, that was used in the B-TRAPPED experiments were fully characterized. Factors investigated included representativeness of the construction and impact of building design features on the natural ventilation and infiltration of outdoor aerosol. Both blower door and perfluorocarbon tracer (PFT) air exchange rate (AER) experiments showed that the ventilation rates of the building were quite typical of similar structures in the New York City (NYC) metropolitan area. Indoor/outdoor (I/O) aerosol count ratios by particle size were comparable to a similar vintage naturally ventilated building in Boston, MA, USA. I/O ratio analyses were consistent with literature findings and showed I/O ratios ranging from 0.310 to 0.601, varying across particle sizes (from 0.3 to 5.0 [corrected] mum) and between first and second floor apartments. An effort to apply the rebound method of Thatcher et al. (Aerosol Sci. Technol., 2003, 37, 847-864) in determining aerosol infiltration rates proved unsuccessful due to unexpectedly long (>60 min) equilibration times after the filtration period. Uninsulated interior wall renovations in the study house created a cavity that resulted in a large intermediate dead volume (for infiltration) that apparently could not be accommodated by a simple infiltration model. Simple two-compartment models evidently have finite application limitations for even modestly complex settings.