2 presentations by Yufei Wei and by Estelle Mennicken

When? 18th June 2021, 14:00-16:00

Where? Webex

The Quadtrees Hubs are to share opinions and discuss research in progress. The meetings of Quadtrees Hubs are open to anyone interested and somehow familiar with some quantitative techniques and willing to progress with these. Please contact Isabelle Pigeron-Piroth isabelle.piroth@uni.lu for more information and obtaining the webex link.

The Effects of Distance to City Centers and Population Size on the NO2 Concentrations in Europe

Yufei Wei (University of Luxembourg, DGEO)

Ground-level NO₂ surface concentrations measured by monitoring stations and tropospheric NO₂ columns from Sentinel-5P are the data sources of NO₂. We filter the data to get the annual mean NO₂ concentrations of European cities. We regress the data to find how urban population size influences the NO₂ concentrations, and how the NO₂ concentrations change within the cities.

The results show larger cities have higher levels of NO₂ concentrations. We also find distinct spatial patterns of the NO₂ concentrations within the cities. The results indicate monitoring stations and Sentinel-5P are reliable in describing and predicting the NO₂ concentrations of European cities.

European urban cores under pressure: quantifying the congestion of trips in and out from city centers as function of population size

Estelle Mennicken (LISER, UDM)

Traffic congestion has many negative social, environmental and economic consequences. We can cite among others the loss of time (hours of delay) inducing productivity and well-being losses, the excess fuel consumption, and the excess emitted CO₂. Understanding and quantifying this phenomenon at the scale of an entire continent is therefore a serious societal challenge. In particular, we focus on comparing the accessibility of city centers based on the geographical location of urban areas but also on the population size. Larger cities benefit from positive agglomeration effects but whether they proportionally show more radial traffic congestion is still an open question.

We simulate intra-urban trips between residential locations and city centers in 303 European cities and retrieve travel information around the clock during a typical weekday. We then compute several congestion indices to reveal the excess time people spend on roads driving during peak traffic time compared to a free-flow situation and establish a city ranking. Second, we observe how the total population size influences the indices. Finally, thanks to previously computed detour indices, we examine the relationship between the physical road network shape and the congestion.

The details of iEMSs 2020 are here.

The followings are the abstract and the video of the presentation Scaling of Urban Heat Island and NO₂ with Urban Population: A Meta-Analysis

Abstract

Due to urban population growth worldwide, thermal anomalies and toxic air pollution are increasing concern for citizens. Despite this increasing challenge and indications that these environmental problems increase with city size, there is still no consolidated understanding of the effect of city size on urban heat island (UHI) and nitrogen dioxide (NO₂) pollution. Meanwhile, research on urban scaling laws, which formally relates population size and urban characteristics, has been quickly increasing over the past decade but is mostly devoted to the socio-economic outcome of cities rather than pollution or heat stress. Most studies dedicated to UHI or NO₂ consider only a single city or analyze a few cities within the top ranks of specific world regions or globally. We intend to fill this gap by conducting a qualitative synthesis of the literature and performing a statistical meta-analysis from published work with the aim to uncover scaling laws of UHI and NO₂ with the population size of cities. Under the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guideline, we collect and filter about 500 research outcomes on UHI and NO₂ from Scopus and Google Scholar. We find that moving from a city with a population of 100-thousand to a city with a population of 1 million, the max UHI intensity increases by 2.66 °C, the annual mean NO₂ surface concentration increases by 14.95 𝜇g/m³. Moving from a city having a population of 1 million to a city with a population of 10-million, the max UHI intensity increases by 3.87 °C, the annual mean NO₂ surface concentration increases by 21.72 𝜇g/m³. Thus, larger cities have higher levels of UHI effects and NO₂ pollution. We also give the progress of verifying the NO₂ scaling using census data and in-situ and RS-measured NO₂ data at the level of Urban Atlas 2012.