Parsimonious Random-Forest-Based Land-Use Regression Model Using Particulate Matter Sensors in Berlin, Germany

Machine learning (ML) methods are widely used in particulate matter prediction modelling, especially through use of air quality sensor data. Despite their advantages, these methods’ black-box nature obscures the understanding of how a prediction has been made. Major issues with these types of models include the data quality and computational intensity. In this study, we employed feature selection methods using recursive feature elimination and global sensitivity analysis for a random-forest (RF)-based land-use regression model developed for the city of Berlin, Germany. Land-use-based predictors, including local climate zones, leaf area index, daily traffic volume, population density, building types, building heights, and street types were used to create a baseline RF model. Five additional models, three using recursive feature elimination method and two using a Sobol-based global sensitivity analysis (GSA), were implemented, and their performance was compared against that of the baseline RF model. The predictors that had a large effect on the prediction as determined using both the methods are discussed. Through feature elimination, the number of predictors were reduced from 220 in the baseline model to eight in the parsimonious models without sacrificing model performance. The model metrics were compared, which showed that the parsimonious_GSA-based model performs better than does the baseline model and reduces the mean absolute error (MAE) from 8.69 µg/m3 to 3.6 µg/m3 and the root mean squared error (RMSE) from 9.86 µg/m3 to 4.23 µg/m3 when applying the trained model to reference station data. The better performance of the GSA_parsimonious model is made possible by the curtailment of the uncertainties propagated through the model via the reduction of multicollinear and redundant predictors. The parsimonious model validated against reference stations was able to predict the PM2.5 concentrations with an MAE of less than 5 µg/m3 for 10 out of 12 locations. The GSA_parsimonious performed best in all model metrics and improved the R2 from 3% in the baseline model to 17%. However, the predictions exhibited a degree of uncertainty, making it unreliable for regional scale modelling. The GSA_parsimonious model can nevertheless be adapted to local scales to highlight the land-use parameters that are indicative of PM2.5 concentrations in Berlin. Overall, population density, leaf area index, and traffic volume are the major predictors of PM2.5, while building type and local climate zones are the less significant predictors. Feature selection based on sensitivity analysis has a large impact on the model performance. Optimising models through sensitivity analysis can enhance the interpretability of the model dynamics and potentially reduce computational costs and time when modelling is performed for larger areas

Calibration Method for Particulate Matter Low-Cost Sensors Used in Ambient Air Quality Monitoring and Research

Over the last decade, manufacturers have come forth with cost-effective sensors for measuring ambient and indoor particulate matter concentration. What these sensors make up for in cost efficiency, they lack in reliability of the measured data due to their sensitivities to temperature and relative humidity. These weaknesses are especially evident when it comes to portable or mobile measurement setups. In recent years many studies have been conducted to assess the possibilities and limitations of these sensors, however mostly restricted to stationary measurements. This study reviews the published literature until 2020 on cost-effective sensors, summarizes the recommendations of experts in the field based on their experiences, and outlines the quantile-mapping methodology to calibrate low-cost sensors in mobile applications. Compared to the commonly used linear regression method, quantile mapping retains the spatial characteristics of the measurements, although a common correction factor cannot be determined. We conclude that quantile mapping can be a useful calibration methodology for mobile measurements given a well-elaborated measurement plan assures providing the necessary data.Bundesministerium für Bildung und ForschungUmweltbundesam

Dreidimensionale Observierung atmosphärischer Prozesse in Städten – 3DOSchlussbericht des Verbundvorhabens 3DOThree-dimensional observation and modeling of atmospheric processes in cities – 3DOfinal report for joint project 3DO

Ziel des BMBF-Programms 'Stadtklima im Wandel' war die Entwicklung, Validierung und Anwendung eines gebäudeauflösenden Stadtklimamodells für ganze Städte. Das Verbundprojekt 3DO übernahm die dem Modul B zugeordneten Forschungsaufgaben: Aufbereitung vorhandener Daten aus der Langzeitbeobachtung (LTO), Aufbau neuer Messstationen, Gewinnung neuer dreidimensionaler atmosphärischer Daten und die Entwicklung neuer Konzepte z.B. zur Modellevaluation. Untersucht wurden der Aufbau der atmosphärischen Grenzschicht, die Charakteristik der meteorologischen Parameter und deren Einfluss auf das thermische Empfinden des Menschen. Ein einheitlicher [UC]2-Datenstandard sowie Analysewerkzeuge wurden entwickelt und in ein Datenmanagementsystem und eine Wissensplattform für den modulübergreifenden Austausch integriert.Aim of the BMBF-Programme 'Urban Climate under Change' was development, validation and application of a building-resolving urban climate model for entire cities. The joint project 3DO took over the research tasks assigned to module B: Preparation of existing data from long-term observation (LTO), deployment of new measuring stations, acquisition of new three-dimensional atmospheric data and new concepts, e.g. for model evaluation. The structure of the atmospheric boundary layer, characteristics of meteorological parameters and their influence on the thermal sensation of humans were investigated. A uniform [UC]2 data standard as well as analysis tools were developed and integrated into a data management system and a knowledge base for cross-module exchange

Dreidimensionale Observierung atmosphärischer Prozesse in Städten – 3DOSchlussbericht des Verbundvorhabens 3DOThree-dimensional observation and modeling of atmospheric processes in cities – 3DOfinal report for joint project 3DO

Ziel des BMBF-Programms 'Stadtklima im Wandel' war die Entwicklung, Validierung und Anwendung eines gebäudeauflösenden Stadtklimamodells für ganze Städte. Das Verbundprojekt 3DO übernahm die dem Modul B zugeordneten Forschungsaufgaben: Aufbereitung vorhandener Daten aus der Langzeitbeobachtung (LTO), Aufbau neuer Messstationen, Gewinnung neuer dreidimensionaler atmosphärischer Daten und die Entwicklung neuer Konzepte z.B. zur Modellevaluation. Untersucht wurden der Aufbau der atmosphärischen Grenzschicht, die Charakteristik der meteorologischen Parameter und deren Einfluss auf das thermische Empfinden des Menschen. Ein einheitlicher [UC]2-Datenstandard sowie Analysewerkzeuge wurden entwickelt und in ein Datenmanagementsystem und eine Wissensplattform für den modulübergreifenden Austausch integriert.Aim of the BMBF-Programme 'Urban Climate under Change' was development, validation and application of a building-resolving urban climate model for entire cities. The joint project 3DO took over the research tasks assigned to module B: Preparation of existing data from long-term observation (LTO), deployment of new measuring stations, acquisition of new three-dimensional atmospheric data and new concepts, e.g. for model evaluation. The structure of the atmospheric boundary layer, characteristics of meteorological parameters and their influence on the thermal sensation of humans were investigated. A uniform [UC]2 data standard as well as analysis tools were developed and integrated into a data management system and a knowledge base for cross-module exchange