Use of CALPUFF for exposure assessment in a near-field, complex terrain setting
ABSTRACT CALPUFF is an atmospheric source-receptor model recommended by the U.S. Environmental Protection Agency for use on a case-by-case basis in complex terrain and wind conditions. The ability of the model to provide useful information for exposure assessments in areas with those topographical and meteorological conditions has received little attention. This is an important knowledge gap for use of CALPUFF outside of regulatory applications, such as exposure analyses conducted in support of risk assessments and health studies. We compared deposition of cadmium (Cd), lead (Pb), and zinc (Zn) calculated with CALPUFF as a result of emissions from a zinc smelter with corresponding concentrations of the metals measured in attic dust and soil samples obtained from the surrounding area. On a point-by-point analysis, predictions from CALPUFF explained 11% (lead) to 53% (zinc) of the variability in concentrations measured in attic dust. Levels of heavy metals in soil interpolated to 100 residential addresses from the distribution of concentrations measured in soil samples also agreed well with deposition predicted with CALPUFF: R2 of 0.46, 0.76, and 079 for Pb, Cd, and Zn, respectively. Community-average concentrations of Cd, Pb, and Zn measured in soil were significantly (p < 0.0001) and strongly correlated (R2 ranged from 0.77 to 0.98) with predicted deposition rates. These findings demonstrate that CALPUFF can provide reasonably accurate predictions of the patterns of long-term air pollutant deposition in the near-field associated with emissions from a discrete source in complex terrain. Because deposition estimates are calculated as a linear function of air concentrations, CALPUFF is expected to be reliable model for prediction of long-term average, near-field ambient air concentrations in complex terrain as well.
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ABSTRACT: A photochemical Eulerian grid modeling system, consisting of MM5/CALMET/CALGRID, was modified to include a process analysis scheme, and a back trajectory method using the CALPUFF model in a reverse diffusion mode was implemented to define the air mass transport path reaching a downwind receptor from urban Seattle, WA. Process analysis was used to determine the relative importance of chemical production, advection, diffusion and deposition within the receptor grid cell and also along the air mass transport path from the urban source area to the receptor. This analysis was applied to an ozone episode occurring during 11–14 July 1996, in the Puget Sound region of Washington State. Within the receptor grid, the process analysis showed that ozone concentrations increase during the day as chemical production exceeds the net effects of deposition and vertical diffusion. Concentrations decrease after mid-afternoon when horizontal advection begins to dominate the other processes. When applied along the air mass transport path, process analysis shows that during most of the day, chemical production is larger than the other processes and causes the air mass ozone concentration to steadily increase during transport downwind of the urban core. Maximum ozone production rates equaled 20–25ppb/h along the trajectory to the rural monitoring site where peak ozone levels occurred approximately 40km downwind of urban Seattle, WA. The chemical production rates during this ozone evolution process play an important role in the peak ozone values. Higher peak ozone concentrations that occurred on Sunday, 14 July 1996 (118ppbv), compared to those on Friday, 12 July 1996 (80ppbv), were due, in part, to the higher ozone production rates along the trajectory to the rural monitoring site on 14 July compared to 12 July. These differences in chemical production appear to be related to differences in VOC/NOx ratios within the urban air mass for each day. The importance of VOC/NOx effects on the 2 days versus differences in meteorology was confirmed by running the simulation for Friday with Sunday emissions and using Sunday meteorological fields with Friday emissions. Differences in emissions for the 2 days produced almost twice the effect on peak ozone concentrations at the downwind receptor compared to the effects of differences in meteorology for these 2 days.Atmospheric Environment - ATMOS ENVIRON. 01/2003; 37(11):1489-1502.
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ABSTRACT: Results of evaluations of transport and dispersion models with field data are summarized. The California Puff (CALPUFF), Hazard Prediction and Assessment Capability (HPAC), and Chemical/Biological Agent Vapor, Liquid, and Solid Tracking (VLSTRACK) models were compared using two recent mesoscale field datasets— the Dipole Pride 26 (DP26) and the Overland Along-wind Dispersion (OLAD). Both field experiments involved instantaneous releases of sulfur hexafluoride tracer gas in a mesoscale region with desert basins and mountains. DP26 involved point sources, and OLAD involved line sources. Networks of surface wind observations and special radiosonde and pilot balloon soundings were available, and tracer concentrations were observed along lines of whole-air samplers and some fast-response instruments at distances up to 20 km. The models were evaluated using the maximum 3-h dosage (concentration integrated over time) along a sampling line. It was found that the solutions were highly dependent upon the diagnostic wind field model used to interpolate the spatially variable observed wind fields. At the DP26 site, CALPUFF and HPAC had better performance than VLSTRACK. Overall, the three models had mean biases within 35% and random scatters of about a factor of 3-4. About 50%-60% of CALPUFF and HPAC predictions and about 40% of VLSTRACK predictions were within a factor of 2 of observations. At the OLAD site, all three models underpredicted by a factor of 2-3, on average, with random scatters of a factor of 3-7. About 50% of HPAC predictions and only 25%-30% of CALPUFF and VLSTRACK predictions were within a factor of 2 of observations.Journal of Applied Meteorology - J APPL METEOROL. 01/2003; 42(4):453-466.
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ABSTRACT: Semi-quantitative food checklists and duplicate beverage samples were collected from up to 80 individuals in Maryland in 1995-1996 in as many as six approximately equally spaced sampling cycles as part of a pilot longitudinal exposure investigation. The duplicate beverage samples were homogenized and analyzed for arsenic (As), cadmium (Cd), chromium (Cr) and lead (Pb) using inductively coupled plasma mass spectrometry (ICP-MS). Metal concentrations (microg/kg) and weights of the duplicate beverage samples (kg/day) were used to derive average daily exposure (microg/day) for each metal. Mixed models and generalized linear models were used to evaluate temporal and population variability of the beverage consumption rates, the log-transformed metal concentrations in the beverage samples, and the associated exposures. The mean number of beverage servings consumed per day was 3.4 (SD 1.9). The temporal variability of the total beverage consumption rates was found to be significant (p = 0.0476). As, Cd, Cr, and Pb were present at quantifiable levels in 93.5, 76.0, 93.5, and 96.7% of the beverage samples, respectively. The mean concentration in the samples was 2.0 (SD 4.4) microg/kg for As, 0.9 (1.6) for Cd, 29.2 (138.5) for Cr, and 2.0 (2.4) for Pb. The mean log-transformed concentrations for As, Cr and Pb and exposure for As varied by as much as a factor of 3 across sampling cycles and were statistically significantly different (p<0.05). Concentrations and exposures of all four metals varied significantly among participants. These findings are discussed with respect to the data collection methods, results from comparable studies, and implications for exposure and risk assessment.Journal of Exposure Analysis and Environmental Epidemiology 01/2000; 10(2):196-205. · 2.72 Impact Factor