Modeling the effects of topography and wind on atmospheric dispersion of CO2 surface leakage at geologic carbon sequestration sites

Understanding the potential impacts of unexpected surface releases of CO{sub 2} is an essential part of risk assessment for geologic carbon sequestration sites. We have extended a mesoscale atmospheric model to model dense gas dispersion of CO{sub 2} leakage. The hazard from CO{sub 2} leakage is greatest in regions with topographic depressions where the dense gas can pool. Simulation of dispersion in idealized topographies shows that CO{sub 2} can persist even under high winds. Simulation of a variety of topographies, winds, and release conditions allows the generation of a catalog of simulation results that can be queried to estimate potential impacts at actual geologic carbon sequestration sites

Quantifying the Air Pollution Exposure Consequences of Distributed Electricity Generation

Private sector and governmental organizations have been promoting the deployment of small-scale, distributed electricity generation (DG) technologies for their many benefits as compared to the traditional paradigm of large, centralized power plants. While some researchers have investigated the impact of a shift toward DG in terms of energy use and even air pollutant concentrations, it is also important to evaluate the air pollutant exposure implications of this shift. We conducted a series of case studies within the state of California that combined air dispersion modeling and inhalation exposure assessment. Twenty-five central stations were selected and five air pollutant-emitting DG technologies were considered, including two that meet the 2003 and 2007 California Air Resources Board DG emissions standards (microturbines and fuel cells with on-site natural gas reformers, respectively). This investigation has revealed that the fraction of pollutant mass emitted that is inhaled by the downwind, exposed population can be more than an order of magnitude greater for all five DG technologies considered than for large, central-station power plants in California. This difference is a consequence mainly of the closer proximity of DG sources to densely populated areas as compared to typical central station, and is independent of the emissions characteristics of the plants assessed. Considering typical emission factors for the five DG technologies, the mass of pollutant inhaled per unit electricity delivered can be up to three orders of magnitude greater for DG units as compared to existing California central stations. To equalize the exposure burden between DG and central station technologies, DG emission factors will need to be reduced to a range between the level of the cleanest, new central stations in California and an order of magnitude below those levels, depending on the pollutant and siting. We conclude that there is reason to caution against an unmitigated embrace of DG technologies that emit air pollutants so that they do not pose a greater public health burden than the current electricity generation system

Inhalation intake of ambient air pollution in California's South Coast Air Basin

Reliable estimates of inhalation intake of air pollution and its distribution among a specified population are important for environmental epidemiology, health risk assessment, urban planning, and environmental policy. We computed distributional characteristics of the inhalation intake of five pollutants for a group of ~25,000 people (~29,000 person-days) living in California’s South Coast Air Basin. Our approach incorporates four main inputs: temporally resolved information about people’s location (latitude and longitude), microenvironment, and activity level; temporally and spatially explicit model determinations of ambient concentrations; stochastically determined microenvironmental adjustment factors relating the exposure concentration to the ambient concentration; and, age-, gender-, and activity-specific breathing rates. Our study is restricted to pollutants of outdoor origin, i.e. it does not incorporate intake in a microenvironment from direct emissions into that microenvironment. Median estimated inhalation intake rates (μgd-1) are 53 for benzene, 5.1 for 1,3-butadiene, 8.7x10-4 for hexavalent chromium in fine particulate matter (Cr-PM2.5), 30 for diesel fine particulate matter (DPM2.5), and 68 for ozone. For the four primary pollutants studied, estimated median intake rates are higher for non-whites and for individuals in low-income households than for the population as a whole. For ozone, a secondary pollutant, the reverse is true. Accounting for microenvironmental adjustment factors, population mobility and temporal correlations between pollutant concentrations and breathing rates affects the estimated inhalation intake by 40% on average. The approach presented here could be extended to quantify the impact on intakes and intake distributions of proposed changes in emissions, air quality, and urban infrastructure