Urban Air Quality Modeling: Evaluating Impacts of Ecoroofs on Urban Air Quality in Portland, Oregon

Danlyn L. Brennan, Portland State University
Selina Teng, University of Washington

This is a podcast summarizing our experience in the altREU where we discuss the project and ask our mentors some questions about the research and why it is important to simulate our environment.


In this work, the authors present a mathematical model simulating the impact of ecoroof vegetation on air quality in an urban microclimate. An ecoroof is a layer of vegetation established on rooftops to reduce stormwater runoff, mitigate heat, and enhance air quality. Certain plant species in ecoroofs may however have a detrimental effect on air quality, due to their emission of biogenic volatile organic compounds (BVOCs), which include potentially reactive species such as isoprene. These chemical species can interact with urban air pollution, particularly NOx produced by car traffic, to create other harmful pollutants such as ozone and particulate matter (PM). With the growing popularity of ecoroofs, it is important for people to have access to tools to investigate possible outcomes of investing in green roof projects that are purported to mitigate air pollution. However, the sophisticated mass transport models currently on the market are expensive and have steep learning curves, creating an access barrier.

To address the need for an easy-to-use, accessible tool to analyze the effect of green roofs on air quality, we created a simple mathematical model simulating the transport of plant emissions in a 1D space with partial differential equations and their numerical solutions. Parameters in the simulation include the volume of the space, emission rates from anthropogenic and biogenic sources, and microclimate data such as wind speed, direction, temperature, and relative humidity. In future work, we hope also to add solar radiation data, deposition, and a diurnally variable boundary condition. This model could be used to inform decisions in the development of green infrastructure in Portland, OR, and contributes to an ongoing research effort at Portland State University exploring the efficacy of green roof compositions including sedums and mosses.