Evaluating the Effects of Radiative Forcing Feedback in Modelling Urban Ozone Air Quality in Portland, Oregon: Two-Way Coupled MM5–CMAQ Numerical Model Simulations

Abstract

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. Background and Study GoalWe can depict in abstract terms (relations 1 and 2) the meteorology-to-chemistry and chemistry-to-meteorology feedbacks of interest in this study and their implications (listed above the brackets) in meteorological and air-quality modelling, viz.

Progress in Urban Greenery Mitigation Science – Assessment Methodologies Advanced Technologies and Impact on Cities

“…The reductions in ground-level ozone resulting from these various pathways, in turn, can help reduce radiative forcing locally, which has been found to be 0.017 W m -2 for each 1 ppbv change in ozone (Taha, Sailor 2010). This feedback effect can cool the air further.…”

Cool Cities: Counteracting Potential Climate Change and its Health Impacts

“…Furthermore, feedbacks from chemistry to meteorology, e.g., radiative forcing, should also be examined further. For example, heat island control measures that can reduce air pollutant concentrations, such as NO, NO 2 , VOC, O 3 , and PM directly (e.g., deposition in vegetation canopies or reduction in emissions) or indirectly (e.g., slowing photochemical production of ozone because of lowered air temperatures) can also affect heating or cooling of the atmosphere because of changes in radiative forcing that result from changes in concentrations of gases and PM [8,18,36,91].…”

Land Covers and Climate Impacts on Land Surface Temperature in Putrajaya, Malaysia

“…Myers & Bernstein (2011) reported how global climate change may affect human health and nutrition resources. Many studies have outlined the direct impacts of climate change, such as heat stress (Heisler & Brazel, 2010;Li, Zhou, Ouyang, Xu, & Zheng, 2012), air pollution (Afroz, Hassan, & Ibrahim, 2003;Taha & Sailor, 2010), and the transmission of infectious diseases (Tomlinson, Chapman, Thornes, & Baker, 2011). Human health is affected by climate change through biogeochemical interactions and the presence of biological responses towards the climate and the atmospheric composition.…”