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Taha H.,Altostratus Inc. | Wilkinson J.,Alpine Geophysics Presently at Golder Assoc. | Bornstein R.,San Jose State University | Xiao Q.,University of California at Davis | And 6 more authors.
Sustainable Cities and Society | Year: 2016

Urban forest strategies of gradually replacing high emitters of biogenic volatile organic compounds (BVOC) with low-emitting species are being considered as voluntary or emerging control measures for maintenance of the 8-h ozone standard in the Sacramento Federal Non-Attainment Area (SFNA). We describe a regulatory modeling study demonstrating the air-quality impacts of such measures as well as of strategies that increase net canopy cover. The results indicate that changing the mix of urban trees can improve air quality. The daily reductions in ozone resulting from species replacement alone reach up to 0.50 ppb. With a more geographically-targeted replacement, the daily reductions increase to 3 ppb. Population-weighted exposure to ozone is reduced by up to 34% relative to the NAAQS (120 ppb) and 12% relative to the CAAQS (90 ppb). The 8-h average peak ozone is reduced by 2%. If, in addition to species replacement, the net canopy cover is increased, the reductions in ozone become much larger but increases in ozone also occur. In some scenarios, the air-quality impacts are 10 times as large as those of only replacing 650,000 trees (control measure). Furthermore, because of the canopy growth (including the replacement trees) relative to 2000-2005, the SFNA is cooled by up to 1.2 °C by 2018 and 1.6 °C by 2023. © 2015 Elsevier Ltd.All rights reserved.

Chen F.,U.S. National Center for Atmospheric Research | Kusaka H.,University of Tsukuba | Bornstein R.,San Jose State University | Ching J.,National Exposure Research Laboratory | And 14 more authors.
International Journal of Climatology | Year: 2011

To bridge the gaps between traditional mesoscale modelling and microscale modelling, the National Center for Atmospheric Research, in collaboration with other agencies and research groups, has developed an integrated urban modelling system coupled to the weather research and forecasting (WRF) model as a community tool to address urban environmental issues. The core of this WRF/urban modelling system consists of the following: (1) three methods with different degrees of freedom to parameterize urban surface processes, ranging from a simple bulk parameterization to a sophisticated multi-layer urban canopy model with an indoor-outdoor exchange sub-model that directly interacts with the atmospheric boundary layer, (2) coupling to fine-scale computational fluid dynamic Reynolds-averaged Navier-Stokes and Large-Eddy simulation models for transport and dispersion (T&D) applications, (3) procedures to incorporate high-resolution urban land use, building morphology, and anthropogenic heating data using the National Urban Database and Access Portal Tool (NUDAPT), and (4) an urbanized high-resolution land data assimilation system. This paper provides an overview of this modelling system; addresses the daunting challenges of initializing the coupled WRF/urban model and of specifying the potentially vast number of parameters required to execute the WRF/urban model; explores the model sensitivity to these urban parameters; and evaluates the ability of WRF/urban to capture urban heat islands, complex boundary-layer structures aloft, and urban plume T&D for several major metropolitan regions. Recent applications of this modelling system illustrate its promising utility, as a regional climate-modelling tool, to investigate impacts of future urbanization on regional meteorological conditions and on air quality under future climate change scenarios. © 2010 Royal Meteorological Society.

Taha H.,Altostratus Inc.
Sustainable Cities and Society | Year: 2015

The goal of this study is to analyze the impacts of urban heat-island control, via increased surface albedo, on regional and urban meteorology, emissions, and ozone air quality over a range of summer conditions in California. The ozone air-quality impacts of heat-island control are then converted into precursor-emission equivalents. Linked atmospheric models used in this effort show that significant cooling of the urban canopy and boundary layers can be achieved, particularly during the daytime, but that warming can also occur. The air-quality improvements are significant where surface albedo is increased. Downwind of modified areas, the air-quality impacts can be positive or negative depending on meteorological conditions affecting the formation, transport, removal, and mixing of ozone and its precursors.Overall, and accounting for both positive and negative impacts of increased urban albedo, the models show beneficial net effects for California. The results do not account for additional benefits such as reduced cooling energy use and associated reductions in emissions from point sources, or the potential negative impacts on heating energy use in winter. These have been addressed elsewhere. This paper is a summary of results from a study and detailed report (Taha, 2013a) that can be accessed at http://www.energy.ca.gov/2013publications/CEC-500-2013-061/CEC-500-2013-061.pdf. © 2015 Elsevier Ltd.

We summarize an on-line coupled meteorological-emissions-photochemical modelling system that allows feedback from air-quality/chemistry to meteorology via radiative forcing. We focus on the radiative-forcing impacts (direct effects) of ozone. We present an application of the coupled modelling system to the episode of 23-31 July 1998 in Portland, Oregon, U. S. A. Results suggest that the inclusion of radiative-forcing feedback produces small but accountable impacts. For this region and episode, stand-alone radiative transfer simulations, i. e., evaluating the effects of radiative forcing independently of changes in meteorology or emissions, suggest that a change of 1 ppb in ground-level ozone is approximately equivalent to a change of 0. 017 W m-2 in radiative forcing. In on-line, coupled, three-dimensional simulations, where the meteorological dependencies are accounted for, domain-wide peak ozone concentrations were higher by 2-4 ppb (relative to a simulated peak of 119.4 ppb) when including the effects of radiative-forcing feedback. A scenario of 10% reduction in anthropogenic emissions produced slightly larger decreases in ozone, an additional 1 ppb in local-peak reductions, relative to scenarios without feedback. © 2010 Springer Science+Business Media B.V.

Taha H.,Altostratus Inc.
International Journal of Low-Carbon Technologies | Year: 2015

There exists a number of environmental and energy measures that, when deployed at urban scale, can directly impact energy use and emissions from power generation and indirectly affect the atmospheric environment which, in turn, impacts energy demand, emissions of greenhouse gas and ozone precursors and photochemical production of ozone. Atmospheric modeling is an important tool in evaluating the indirect effects, both beneficial and inadvertent, of urban heat-island mitigation. In this article, we provide a brief background discussion of heat-island research and modeling and present findings from three recent projects we have completed for California. © The Author 2013.

Among the many benefits of solar photovoltaic (PV) systems, the direct effects are those of providing local power and the indirect ones include avoided generation from fossil-fuel power plants. The latter translate into reduced emissions of greenhouse gas (thus reduced radiative forcing) and other pollutants, such as ozone precursors (thus improved air quality). Because large-scale PV deployments can alter the radiative balance at the surface-atmosphere interface, they can exert certain impacts on the temperature and flow fields.In this analysis, meteorological modeling was performed for the Los Angeles region as a case study to evaluate the potential atmospheric effects of solar PV deployment. The simulations show no adverse impacts on air temperature and urban heat islands from large-scale PV deployment. For the range of solar conversion efficiencies currently available or expected to become attainable in the near future, the deployment of solar PV can cool the urban environment. The cooling can reach up to 0.2. C in the Los Angeles region. Under hypothetical future-year scenarios of cool cities (urban areas with extensive implementations of highly-reflective roofs and pavements) and high-density deployments of urban solar PV arrays, some adverse impacts (0.1. C or less in warming) might occur. However, such extreme high-density deployments of cool surfaces are not expected and thus the warming effects are unlikely to result. © 2012 Elsevier Ltd.

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