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Satellite observations confirm: Air quality in Helsinki improves during the weekend

Satellite observations confirm: Air quality in Helsinki improves during the weekend

Space-borne and ground-based pollution measurements show similar weekly and seasonal cycle.

New research shows that satellite-based nitrogen oxide observations can be applied for air quality monitoring in Helsinki. Nitrogen dioxide (NO2) is a polluting gas, produced mainly in combustion processes (e.g., from car traffic, industrial and energy production) and toxic when present in high concentrations at the surface. NO2 is a short-lived gas and thus, remains mostly close to the emission sources.

"The results show that the NO2-concentrations in the atmosphere are smaller during the weekend, when the polluting emissions from car traffic and industrial production are reduced compared to the working days. Also, the NO2 amount decreases during summer season, when the accelerated photochemistry destroys NO2-molecules more efficiently and the anthropogenic emissions are reduced." says FMI researcher Iolanda Ialongo.

OMI-instrument provides accurate NO2 observations also at high latitudes

The Ozone Monitoring Instrument (OMI), flying onboard NASA's Aura satellite, has been providing NO2 concentrations in the troposphere (the atmospheric layer closer to the Earth's surface) since October 2004, with almost-daily coverage of the globe. OMI is a Dutch-Finnish instrument measuring the solar radiation backscattered by the Earth's atmosphere and surface in the UV-visible range.

OMI NO2-observations were compared to ground-based measurements performed in Helsinki-Kumpula station, derived from both Pandora-spectrometer and SMEAR-air quality station instrument. Retrieving NO2-concentrations at high latitude site (as Helsinki) is challenging because of the cloud contamination as well as the lack of solar radiation. Despites these limitations, satellite-based NO2-observations in Helsinki agree within the uncertainties with the ground-based measurements and are able to similarly describe the air quality features (e.g., weekly and seasonal cycle).

The results of the research support the Key Funding ILMApilot-project funded by the Academy of Finland. The project aims at increasing the societal impact of satellite-based atmospheric observations for air quality monitoring. The project is implemented in collaboration with HSY (Helsinki Region Environmental Services Authority).

 

Figure: NO2 weekly and seasonal cycle (left and right, respectively). NO2 levels are reduced during the weekend and in summer.

For more information:

Researcher Iolanda Ialongo, iolanda.ialongo@fmi.fi

Reference:

Ialongo, I., Herman, J., Krotkov, N., Lamsal, L., Boersma, K. F., Hovila, J., and Tamminen, J.: Comparison of OMI NO2 observations and their seasonal and weekly cycles with ground-based measurements in Helsinki, Atmos. Meas. Tech., 9, 5203-5212, doi:10.51


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