Vergleich der troposphärischen NO2-Variabilität auf Basis von satellitengestützten Beobachtungen für Los Angeles, Tokio und die Po-Ebene

Kurzfassung

Trace gases in the atmosphere are often studied in the context of urban health. Due to high local anthropogenic pollutant emissions, densely populated areas in particular represent a hot-spot of air pollution. To address this challenge, a better understanding of the sources, reactions and transport processes of trace gases is important. The aim of this bachelor thesis is to explain the causes of the fluctuations in the tropospheric pollution of the air pollutant nitrogen dioxide (NO2). The observation period extends from 2004 to 2023 and the study areas include the Po Valley, Los Angeles, Tokyo and the European metropolitan regions of Paris, Berlin, Vienna, Milan and Madrid. The Po Valley, Los Angeles and Tokyo have different climatic conditions but similar topographical features, as they are surrounded by mountain and hills on several sides. This basin structure leads to the accumulation of pollutants. This work focuses on the gas NO2, which is analyzed using satellite observations from the GOME-2 and OMI instruments on board of the MetOp-A and -B and the Aura satellites. The selected satellites Aura and MetOp-A and -B have different equator crossing times (ETC) at 13:45 asc and 09:30 desc. Using wavelet analysis, a comparison between the variability of two to four months and economic activity in the Po Valley can be carried out for both overflight times. Both fluctuations in NO2-pollution and gross domestic product (GDP) per capita over Italy are predominantly small between 2009 and 2016. Furthermore, oscillations of known circulation patterns such as the quasi-biennialoscillation (QBO) could be detected in the time series by using the empirical mode decomposition (EMD) method. The agreement with the QBO, whose westerly wind phases coincides with the maxima of a quasi-biennial variability in the time series, is particularly pronounced. Finally, a relationship between the short-term variability of NO2 and traffic is analyzed in all study areas, since traffic emissions account as one of the major sources for anthropogenic NO2-pollution. The different volume of traffic on weekdays and weekends leads to a seven-day fluctuation in the NO2-emissions. In addition, further fluctuations at the periodicity of around three days is recognizable in many years. As a result, an indicator is formed that reflects the ratio of the three-day fluctuation compared to the seven-day fluctuation. In particular during the COVID-19 pandemic, the indicator shows a significant increase in the signal in all regions. At the same time a high use of home office regarding to worldwide lockdown and thus a higher variability in the commuting behavior of employees can be identified. As shown in (Bichler und Bittner 2022), economic crises can lead to a significant decrease of NO2-variability. This is shown by the data on car use in the Po Valley, which declined during the economic crisis from 2009 to 2016.