Open Access

Rosina Engert, Renée Bichler, Michael Bittner

• This study investigates the temporal variability of tropospheric NO2 vertical column density over Milan in Italy and its surrounding area using daily satellite observations from Aura/OMI over the period of 2004 to 2023. The analysis reveals a significant long-term decrease of 55% in NO2 pollution which is consistent with previous studies. Using spectral analysis techniques such as wavelet and harmonic analysis, we identified distinct oscillation patterns such as an annual cycle linked to seasonal heating and NO2 lifetime variations, and shorter-term variabilities of 6.5-7.5 days (I7) as well as two to five days (I3). The I7 pattern, attributed to weekly traffic variations, shows consistent presence throughout the study period, while I3 exhibits notable temporal variations. The I3/ I7 ratio demonstrates significant shifts corresponding to major economic events, including the 2008 global economic crisis and the COVID-19 pandemic. Notably, the increased adoption of remote work during theThis study investigates the temporal variability of tropospheric NO2 vertical column density over Milan in Italy and its surrounding area using daily satellite observations from Aura/OMI over the period of 2004 to 2023. The analysis reveals a significant long-term decrease of 55% in NO2 pollution which is consistent with previous studies. Using spectral analysis techniques such as wavelet and harmonic analysis, we identified distinct oscillation patterns such as an annual cycle linked to seasonal heating and NO2 lifetime variations, and shorter-term variabilities of 6.5-7.5 days (I7) as well as two to five days (I3). The I7 pattern, attributed to weekly traffic variations, shows consistent presence throughout the study period, while I3 exhibits notable temporal variations. The I3/ I7 ratio demonstrates significant shifts corresponding to major economic events, including the 2008 global economic crisis and the COVID-19 pandemic. Notably, the increased adoption of remote work during the pandemic (2.5% to 12% between 2019 and 2021) disrupted traditional weekly commuting patterns, reflected in enhanced I3 dominance. This study establishes a clear connection between economic activities, commuting behavior, and NO2 variability patterns, demonstrating how the shift to remote work, leaves distinct signatures in atmospheric NO2 variability.…