IASI carbon monoxide validation over the Arctic during POLARCAT spring and summer campaigns

International audienceIn this paper, we provide a detailed comparison between carbon monoxide (CO) data measured by the Infrared Atmospheric Sounding Interferometer (IASI)/METOP and aircraft measurements over the Arctic. The CO measurements were obtained during North American campaigns (NASA ARCTAS and NOAA ARCPAC) and European campaigns (POLARCAT-France, POLARCAT-GRACE and YAK-AEROSIB) as part of the International Polar Year (IPY) in spring and summer 2008. During the campaigns different air masses were sampled including clean air, polluted plumes originating from anthropogenic sources in Europe, Asia and North America, and forest fire plumes originating from Siberia and Canada. CO-rich plumes following different transport pathways were captured well by the IASI instrument, illustrated for example by a transport event over the North Pole from Asia on 9 July 2008. The comparison between the IASI CO profiles and aircraft data was achieved by first completing the latter for higher altitudes using a latitudinally dependent climatology of ACE-FTS satellite CO profiles (2004–2009) and by subsequently smoothing the resulting full profiles by the IASI averaging kernels. Proceeding this way, the IASI profiles were shown to be in good agreement with smoothed in situ profiles (with a difference of about 10 ppbv) in spring. In summer, the IASI profiles were higher than the smoothed in situ profiles below 8 km, for all polluted cases. Correlations between IASI and combination ACE-FTS/aircraft derived total columns varied from 0.15 to 0.74 in spring and 0.26 to 0.84 in summer, with better results over the sea in spring (0.73) and over the land in summer (0.69)