Figure 1. Monthly multiyear (2008-2018) mean IASI
NH3. Data are gridded to 0.1° × 0.1° using oversampling
(see text for details). Grey grids, limited to Scotland, have
< 10 observations.
Figure 1 shows the gridded March-September multiyear monthly mean IASI
NH3 columns. The number of observations in each grid
ranges from 11 to 128. Values over Scotland are very low (typically
< 2 × 1015 molecules cm-2)
due to weak signal, lower agricultural activity than the rest of the UK,
and greater distance from sources in mainland Europe. The range in IASI
NH3 over the rest of the country of 4-8 ×
1015 molecules cm-2 is much less
than the NH3 hotspots in other parts of the world.
Columns over global hotspots such as North China, West Africa, the Po
Valley (Italy), and the Indo-Gangetic Plain (India) exceed 2 ×
1016 molecules cm-2 (Cady-Pereira et
al., 2017; Dammers et al., 2019; Van Damme et al., 2014b; 2018). These
are associated with industrial and agricultural activity in India and
China, and intense seasonal open burning of biomass and relatively low
abundance of acidic aerosols in West Africa and northern India. Warm
temperatures in these regions also increase NH3emissions, suppress partitioning of NH3 to aerosols, and
enhance the spectral signal.