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951.
Charles W. Gruber 《Journal of the Air & Waste Management Association (1995)》2013,63(4):402-403
Abstract This work assessed the usefulness of a current air quality model (American Meteorological Society/Environmental Protection Agency Regulatory Model [AERMOD]) for predicting air concentrations and deposition of perfluorooctanoate (PFO) near a manufacturing facility. Air quality models play an important role in providing information for verifying permitting conditions and for exposure assessment purposes. It is important to ensure traditional modeling approaches are applicable to perfluorinated compounds, which are known to have unusual properties. Measured field data were compared with modeling predictions to show that AERMOD adequately located the maximum air concentration in the study area, provided representative or conservative air concentration estimates, and demonstrated bias and scatter not significantly different than that reported for other compounds. Surface soil/grass concentrations resulting from modeled deposition flux also showed acceptable bias and scatter compared with measured concentrations of PFO in soil/grass samples. Errors in predictions of air concentrations or deposition may be best explained by meteorological input uncertainty and conservatism in the PRIME algorithm used to account for building downwash. In general, AERMOD was found to be a useful screening tool for modeling the dispersion and deposition of PFO in air near a manufacturing facility. 相似文献
952.
Charles F. Contant Thomas H. Stock Patricia A. Buffler Alfonso H. Holguin Brenda M. Gehan Dennis J. Kotchmar 《Journal of the Air & Waste Management Association (1995)》2013,63(5):587-594
Estimates of individual personal exposures to ozone, nitrogen dioxide, pollen, temperature, and relative humidity for a group of asthmatics participating In a health effects study were obtained by means of a modeling approach utilizing fixed site monitoring data, regression relationships between fixed site and indoor and outdoor micro-environment concentrations, study subject activity patterns, and study household characteristics. A considerable improvement in the accuracy of exposure assessment using the exposure model instead of fixed site measurements alone was demonstrated for ozone. This large refinement of ozone exposure estimates was achieved using a simplified approach which emphasized the large differences between Indoor and outdoor micro-environmental concentrations, and assumed relatively little heterogeneity in exposure within either of these two broad micro-environmental categories. Major sources of error in the exposure model for ozone Include: failure to Include Indoor microenvironments with no air conditioning in the development of the model, Inability to accurately apportion within-hour time spent in different microenvironments, and misclassification of hour-specific personal location by study subjects. 相似文献
953.
Helen C. Shields Charles J. Weschler 《Journal of the Air & Waste Management Association (1995)》2013,63(9):1039-1045
Volatile organic compounds can contribute to the failure of electronic equipment in both switching offices and data centers. They can also be useful indicators of ventilation needs. Only within the past decade have ambient concentrations of volatile organics been measured routinely. In standard sampling approach, a pump is used to pull a known volume of air through an adsorbent. This study examines a sampling procedure that does not use a pump, but instead depends on molecular diffusion for eventual contact between the vapor phase compounds and the charcoal sorbent (passive sampling). The technique is both simpler and less expensive than active sampling with a pump. This method has been validated for low-level sampling over extended time intervals. This study demonstrates that collected amounts vary linearly with airborne concentrations for sampling intervals in excess of four weeks: even after eight weeks of sampling at typical ambient concentrations, the amount of material collected does not approach the capacity of the sorbent. The method is applicable for concentrations spanning six orders of magnitude; reproducibility averages 13 percent of the mean value; and the sensitivity is excellent (0.06 μg/m3 or roughly 0.015 ppbv for a compound with a molecular weight of 100). The procedure has already been used successfully to monitor indoor air quality at almost a dozen telephone office and data center sites. 相似文献
954.
Thomas H. Stock Dennis J. Kotchmar Charles F. Contant Patricia A. Buffler Alfonso H. Holguin Brenda M. Gehan 《Journal of the Air & Waste Management Association (1995)》2013,63(12):1266-1273
In order to provide reliable pollutant and meteorological exposure estimates for an epidemiological study of asthmatics residing in two Houston neighborhoods, a dedicated three-tier air monitoring system was established. This consisted of fixed site ambient air monitoring at the center of each study area, a mobile van performing simultaneous indoor and outdoor measurements at selected residences of study participants, and a limited amount of direct personal monitoring for half of the participants. Monitored pollutants Included all criteria pollutant gases, as well as aeroallergens, aldehydes, TSP, and IP. Laboratory analyses provided concentrations of sulfate, nitrate, and trace elements. Continuous measurements of several meteorological parameters also were obtained. Intensive quality assurance and data validation efforts resulted in a high percentage of valid data for most pollutants. Ozone was the only measured pollutant that exceeded the NAAQS during the six-month (May to October) study period. The monitoring scheme allowed important pollutant concentration differences to be detected between day and night, between Indoors and outdoors, and among various indoor environments. The use of these monitoring data in combination with personal activity and household characteristics data to generate estimates of personal exposures for the epidemiological analysis will be described in a subsequent paper. 相似文献
955.
Wojciech Jozewicz John C. S. Chang Charles B. Sedman Theodore G. Brna 《Journal of the Air & Waste Management Association (1995)》2013,63(8):1027-1034
Novel silica-enhanced lime sorbents were tested in a bench-scale sand-bed reactor for their potential for SO2 removal from flue gas. Reactor conditions were 64°C (147°F), relative humidity of 60 percent [corresponding to an approach to saturation temperature of 10°C (18°F)], and inlet SO2 concentration of 500 or 1000 ppm. The sorbents were prepared by pressure hydration of CaO or Ca(OH)2 with siliceous materials at 100°C (101 kPa) [212°F (14.7 psi)] to 230°C (2793 kPa) [446°F (405 psi)] for 15 min to 4 h. Pressure hydration fostered the formation of a sorbent reactive with SO2 from fly ash and Ca(OH)2 in a much shorter time than did atmospheric hydration. The conversion of Ca(OH)2 in the sand-bed reactor increased with the increasing weight ratio of fly ash to lime and correlated well with B.E.T. surface area, increasing with increasing surface area. The optimum temperature range for the pressure-hydration of fly ash with Ca(OH)2 was between 110 and 160°C (230 and 320 °F). The pressure hydration of diatomaceous earth with CaO did not offer significant reactivity advantages over atmospheric hydration; however, the rate of enhancement of Ca(OH)2 conversions was much faster with pressure hydration. Scanning electron microscope (SEM) and x-ray diffraction studies showed solids of different morphology with different fly ash/lime ratios and changing conditions of pressure hydration. 相似文献
956.
957.
Ernstson H van der Leeuw SE Redman CL Meffert DJ Davis G Alfsen C Elmqvist T 《Ambio》2010,39(8):531-545
Urbanization is a global multidimensional process paired with increasing uncertainty due to climate change, migration of people,
and changes in the capacity to sustain ecosystem services. This article lays a foundation for discussing transitions in urban
governance, which enable cities to navigate change, build capacity to withstand shocks, and use experimentation and innovation
in face of uncertainty. Using the three concrete case cities—New Orleans, Cape Town, and Phoenix—the article analyzes thresholds
and cross-scale interactions, and expands the scale at which urban resilience has been discussed by integrating the idea from
geography that cities form part of “system of cities” (i.e., they cannot be seen as single entities). Based on this, the article
argues that urban governance need to harness social networks of urban innovation to sustain ecosystem services, while nurturing
discourses that situate the city as part of regional ecosystems. The article broadens the discussion on urban resilience while
challenging resilience theory when addressing human-dominated ecosystems. Practical examples of harnessing urban innovation
are presented, paired with an agenda for research and policy. 相似文献
958.
James F. Cruise Charles A. Laymon Osama Z. Al-Hamdan 《Journal of the American Water Resources Association》2010,46(6):1159-1170
Cruise, James F., Charles A. Laymon, and Osama Z. Al-Hamdan, 2010. Impact of 20 Years of Land-Cover Change on the Hydrology of Streams in the Southeastern United States. Journal of the American Water Resources Association (JAWRA) 46(6):1159–1170. DOI: 10.1111/j.1752-1688.2010.00483.x Abstract: Land-cover changes for portions of Alabama, Georgia, and Tennessee were estimated for the years 1980, 1990, and 2000 using classified Landsat images, and associated with hydrologic indices for 12 watersheds in the region. Rainfall-adjusted mean annual streamflow, an ET proxy (precipitation minus runoff), frequency of inundation above thresholds, and duration of inundation were used to characterize the hydrologic response of the test basins over the two-decade study period. Results indicate that several of the watersheds had undergone significant (>20%) reductions in agricultural land cover with a coincident increase in forested land. Attempts to correlate the hydrologic results with the land-cover changes were only partially successful. Watersheds with the largest land conversion from agriculture to forest (20% or more) did show significant trends in hydrologic indices indicating decreasing streamflow; however, other basins evidenced ambiguous results. The net conclusions of the study are that land-cover effects on hydrologic variables may be nuanced and can sometimes be only indirectly evident, and that a rigorous and detailed land-cover classification effort along with a battery of statistical tests with the same objective may be necessary to uncover these effects. 相似文献
959.
Charles McDade Ivar Tombach Susanne Hering Nathan Kreisberg 《Journal of the Air & Waste Management Association (1995)》2013,63(5):849-857
ABSTRACT Wintertime atmospheric light scattering in Dallas, TX, was estimated through the use of aerosol models. Input data for the aerosol models were provided by measurements of aerosol chemistry, physical particle size distributions, and distributions of particulate sulfur by particle size, and by predictions by an atmospheric simulation model. Light scattering measurements provided a basis for testing the aerosol models. The SCAPE thermodynamic equilibrium model was used to estimate the amount of liquid water associated with particles and the ELSIE Mie scattering model was applied to estimate the resulting light scattering. The calculations were based on aerosol properties measured in Dallas during December 1994 and February 1995, and changes in scattering due to hypothetical changes in the aerosol were predicted. The predicted light scattering was compared to scattering measured by an Optec nephelom-eter; agreement was within 20% in every case. 相似文献
960.
Charles McDade Ivar Tombach Christian Seigneur Peter K. Mueller Pradeep Saxena 《Journal of the Air & Waste Management Association (1995)》2013,63(5):826-834
ABSTRACT A study was conducted to estimate the changes in wintertime visual air quality in Dallas-Fort Worth (DFW) that might occur due to proposed reductions in SO2 emissions at two steam electric generating plants in eastern Texas, each over 100 km from the city. To provide information for designing subsequent investigations, the haze was characterized broadly during the first year of the study. Meteorological data acquired then demonstrated that, during haze episodes, emissions from only one of the two plants were likely to be transported directly to DFW. Therefore, the second year of the study was centered on just one of the power plants. Air quality was then characterized within the urban area and at rural locations that would be upwind and downwind of the plant during transport to DFW. An instrumented aircraft measured plume dispersion and the air surrounding the plume on selected days. A mathematical model was used to predict the change that would occur in airborne particulate matter concentrations in DFW if SO2 emissions were reduced to reflect the proposed limitations. The contribution of particles in the atmosphere to light extinction was estimated, and simulated photographs were produced to illustrate the visibility changes. The study concluded that the proposed emission reductions would, at most, subtly change perceived wintertime visibility. 相似文献