Satellite evidence for changes in the NO₂ weekly cycle over large cities

Area of Science:

• Atmospheric Chemistry
• Environmental Science
• Remote Sensing

Background:

• Anthropogenic activities are the primary source of atmospheric nitrogen oxides (NOx).
• NOx emissions lead to a distinct weekly cycle in urban nitrogen dioxide (NO2) concentrations.
• Understanding these cycles is crucial for air quality management and emission trend analysis.

Purpose of the Study:

• To analyze long-term trends in the weekly cycle of urban NO2 abundances.
• To investigate the drivers behind changes in the weekly NO2 cycle, particularly the role of NOx emissions.
• To validate findings using multiple satellite datasets and atmospheric modeling.

Main Methods:

• Comprehensive analysis of the 2005-2017 Ozone Monitoring Instrument (OMI) NO2 dataset.
• Corroboration with a year of high-resolution TROPOspheric Monitoring Instrument (TROPOMI) NO2 observations.
• Utilizing the MAGRITTEv1.1 chemistry-transport model for multiyear simulations over the U.S. and the Middle East.

Main Results:

• Significant weekly NO2 cycles were detected in 115 out of 274 analyzed cities.
• A clear weakening of the weekly cycle was observed in European and U.S. cities, linked to declining anthropogenic emissions.
• Sunday NO2 columns in U.S. cities increased relative to the weekly average from 0.72 (2005-2007) to 0.88 (2015-2017).
• Conversely, regions with rapid emission growth showed the opposite trend.
• The MAGRITTE model successfully replicated observed weekly cycles and trends in major cities.

Conclusions:

• The study confirms a weakening weekly NO2 cycle in developed regions due to emission reductions and increasing background NO2.
• Satellite data and modeling provide robust evidence of changing urban air pollution dynamics.
• These findings highlight the impact of emission control strategies on atmospheric pollutant cycles and inform future air quality policies.