Wind and turbulence relationship with NO2 in an urban environment: a fine-scale observational analysis

• Published in: Urban climate Vol. 51; p. 101663
• Main Authors: Román-Cascón, C., Yagüe, C., Ortiz-Corral, P., Serrano, E., Sánchez, B., Sastre, M., Maqueda, G., Alonso-Blanco, E., Artiñano, B., Gómez-Moreno, F.J., Diaz-Ramiro, E., Fernández, J., Martilli, A., García, A.M., Núñez, A., Cordero, J.M., Narros, A., Borge, R.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.09.2023
• Subjects: Air pollution; AIRTEC-CM; Boundary-layer turbulence; Breezes; Stable conditions; Wind; Stable conditions; AIRTEC-CM; Wind; Air pollution; Boundary-layer turbulence; Breezes
• ISSN: 2212-0955; 2212-0955
• DOI: 10.1016/j.uclim.2023.101663

It is well known that meteorology plays an important role in the diurnal evolution of pollutants, especially those variables related to atmospheric dispersion. Most studies typically relate the concentration of some pollutants with wind speed from conventional anemometers; however, the use of turbulence variables is less common, in part because the needed instruments are not so typical in standard air-quality stations. In this work, we compare the wind-NO2 relationship with the turbulence-NO2 one using observational data from two field campaigns developed in Madrid (winter and summer). The turbulence data comes from two sonic anemometers deployed at different locations: one close to the street and the other at the top of a nearby tall building. The results indicate that the turbulent variables correlate better with the pollutant concentration than the wind speed when using data from the street sonic, while the contrary is found when using the terrace sonic. These data are also used to perform a fine-scale analysis of the turbulent diffusion-NO2 behaviour during a very-stable period in winter, when the turbulence typically shows a decrease in the evening transition, causing the highestNO2 concentrations. Conversely, under these conditions, the formation of thermally-driven winds is also favoured later in the night, which favours the pollutant dispersion and cleaning of the air. The important role of these dynamical processes on the NO2 evolution highlights the importance of the correct understanding of small-scale atmospheric processes to understand their relationship with the concentration of pollutants. •Turbulence measurements relate better to NO2 concentration than wind speed.•Sonic anemometers located at the street level provide adequate estimations of diffusion.•The highest NO2 concentrations are found during the evening transition of stable days.•Thermally-driven flows formed in the nighttime of stable days clean the air effectively.•The NO2 concentration is highly affected by transient dynamical phenomena.