First Advisor

Elliott Gall

Term of Graduation

January 2021

Date of Publication

Summer 9-27-2018

Document Type

Thesis

Degree Name

Master of Science (M.S.) in Mechanical Engineering

Department

Mechanical Engineering

Language

English

Subjects

Green roofs (Gardening) -- Environmental aspects, Ozone-depleting substance mitigation, Indoor air quality

DOI

10.15760/etd.6437

Physical Description

1 online resource (vi, 115 pages)

Abstract

Ozone in indoor environments can pose a health risk to human occupants; around half of exposure to this pollutant occurs inside buildings. One approach to reducing indoor O3 levels is to mitigate O3 as it enters a building via outdoor air ventilation supply. Often, mechanical systems that introduce outdoor air into buildings are placed on building rooftops. At the urban scale, greenery has been shown to reduce levels of some harmful pollutants, including ozone and cities like Portland, OR, are mandating green roofs be built on large commercial buildings to increase urban green surfaces. We investigate if rooftop vegetation may act as a sink for O3 as transport occurs across a green roof. It is known that O3 can react with vegetated surfaces and the ground but there is scant empirical research on said pollutant dynamics on vegetated green roofs, and little data concerning pollutant interactions occurring on other rooftop designs. Essentially unstudied is the potential of rooftop designs to affect local concentrations of pollutants where building outdoor air supply may be co-located. In this study, we investigate O3 dry deposition using resistance uptake theory in an area that includes a green roof on a local big box retail store through a field study conducted during a two-week period in the Summer of 2017. Deposition velocities and subsequently surface resistances were measured. The 10th, 50th, and 90th percentiles for resistances were 54.8 s/m, 195.3 s/m, and 3692.9 s/m respectively. A 2-D advection-diffusion model of rooftop deposition is employed to describe transport across the green roof and sensitivity analysis was performed to compare the impact of different parameters. The sensitivity analysis demonstrated that the fetch length and the vegetation height had the biggest impact, followed by the meteorological parameters; the friction velocity and heat flux. The surface resistance had the least impact on deposition. An ideal case was used to demonstrate that even when conditions are maximized for deposition, the impact on the concentration gradient is minimal at best.

Rights

In Copyright. URI: http://rightsstatements.org/vocab/InC/1.0/ This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).

Persistent Identifier

https://archives.pdx.edu/ds/psu/26521

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