Modelling Resilient Measures to Climate Change Impacts on Urban Air Quality

Abstract

Considering different resilience measures such as the increase of urban green areas and the application of white roofs, a set of resilience scenarios were evaluated with a cascade of numerical models (MPI-ESM-LR/WRF/CAMx) using as case study a future heat wave occurring in Porto (Portugal) urban area. Meteorological forcing and boundary data was derived from the CMIP5 earth system model MPI-ESM (Representative Concentration Pathway RCP 8.5) downscaled to Porto urban area. The influence of different resilience scenarios on the air quality was quantified and compared for the different scenarios. The results show that all tested measures lead to an increased resilience to CC impacts, promoting the reduction of ozone concentrations. The application of green roofs was the measure that shows more benefits to air quality.

Questions and Answers

Questioner: Stefano Alessandrini

Question: In a similar study over the city of Chicago they observed a negative feedback over air pollution due to introduction of green roofs. In fact, the sea-land temperature gradient tend to decrease, reducing the sea breeze. Why you didn’t observe such an effect?

Answer: It is a fact that the sea-breeze affect part of the days over the study region. Nevertheless, this thermal circulation does not prevail during the heat wave study period, so it was not possible to conclude about it influence on this particular study.

Questioner: Sebnem Aksoyoğlu

Question: Did you take into account the change in biogenic emissions in your green roof, green park scenarios?

Answer: No, we didn’t. But we are now presently considering it in our modeling tests.

Questioner: V. Kallos

Question: I wonder about the large decrease on ozone on the green roof scenario by more than 30%. Did you look into the main mechanisms that are responsible for this decrease?

Answer: The objective of this study was to analyze the differences obtained by our (extensively validated) modeling system when different type of resilient measures is considered in order to select the most appropriated to be studied. In this sense, it was not yet performed a detailed analysis about the mechanism responsible for such behavior. This will be the next phase after selecting the most efficient and resilient measures to be adopted.

Questioner: Jaakko Kukkonen

Question: Have you considered the potential increased allergenic pollen concentrations? Many tree and grass species cause adverse health effects for humans, due to allergenicity. It would therefore be important to select the plant species carefully, also allowing for this issue.

Answer: No, the associated pollen concentrations were not considered in the present work. Nevertheless, we agree that this should be taken into account when selecting the plants of the green roof/parks. We intend to include the pollen simulation in our dispersion models, but first this requires several tests and validation procedures, still under development.

Questioner: Heinke Schlünzen

Question: How is the green roof considered in the modelling? Is evaporating “solucing” the available water reservoir and eventually can the green on the roof dry out?

Answer: The green roof was considered in the same way as the green areas existent in the rest of the domain.

Question: Are the albedo values changed in the meteorology model consistently used in the chemistry part (lower for green, higher for white)? Is the neglected radiation considered in the photochemical reactions leading to ozone formation?

Answer: Yes, the change in albedo was considered in the simulation, but the role of the neglected radiation was not quantified.