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. 2012 Feb 16;2:265. doi: 10.1038/srep00265

Figure 1. 2004–2010 timeseries of OMI tropospheric NO2 column observations over the city of Madrid.

Figure 1

Grey circles indicate daily observations and blue circles the monthly average for cloud-free conditions (cloud radiance fraction below 0.5). The red line shows the low-pass (KZ) filtered NO2 column signal as a result of 6 iterations of a 103-day moving average filter (n103,6(t)) (see Methods).