News6.8.2014

Satellite observations provide information about the changes in air pollution from cities and ships in the Baltic Sea region

Satellite data are very important for air quality monitoring over large areas where ground-based and aircraft measurements are not available.

For example, in the Baltic Sea marine and coastal areas, industries, cars and ships emit polluting species such as nitrogen dioxide (NO2) in the atmosphere. NO2 is a pollutant mainly generated by combustion processes and it is toxic when present at high concentrations close to the Earth's surface.

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. Short-lived air pollutants of anthropogenic origin, such as NO2, remain mainly close to emission sources and, therefore, can be used to quantify the changes in polluting emissions.

Summer mean NO2 values from OMI show the largest coastal cities and the main shipping lane in the Baltic Sea. Fitting the NO2 patterns with a theoretical model describing the decay of the signal from the city center allows one estimating the NO2 emissions and lifetime for urban sources from satellite observations. In Helsinki, these values are estimated as E'=(1.5±0.4) mol/s and =(3±1) h, respectively, in agreement with the existing emission databases.

Furthermore, the OMI NO2 observations over the open sea were compared to the ship emission data derived from model calculations. The results showed similar year-to-year variability, with a drop in year 2009, corresponding to the effect of reduced ship traffic during the economical crisis.

This means that OMI is sensitive to the signal coming from very weak emission sources and that NO2 data can be used to detect changes in atmospheric pollution coming from different emission sources in the Baltic Sea region. This is the first study in which satellite-based NO2 observations were used to monitor such weak emission sources. So far, satellite data were used mostly to study areas with strong emissions, such as China, eastern U.S. and central Europe.

Summer mean tropospheric NO2 (molec./cm2) during years 2005-2010.

For more information:

Researcher Iolanda Ialongo, iolanda.ialongo@fmi.fi, tel. +358 50 380 3085

Reference: Ialongo, I., Hakkarainen, J., Hyttinen, N., Jalkanen, J.-P., Johansson, L., Boersma, K. F., Krotkov, N., and Tamminen, J.: Characterization of OMI tropospheric NO2 over the Baltic Sea region, Atmos. Chem. Phys., 14, 7795-7805, doi:10.5194/acp-14-7795-2014, 2014.

http://www.atmos-chem-phys-discuss.net/14/2021/2014/acpd-14-2021-2014.html