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Zusammenfassung:
In this study, spatial and temporal distributions of tropospheric NO2
vertical column densities over Pakistan during the time period of
2002-2012 are discussed. Data products from the satellite instrument
SCIAMACHY are used. The results show a large NO2 growth over major
cities of Pakistan, particularly the areas with rapid urbanization.
Different seasonal cycles were observed in different regions of
Pakistan. In the provinces of Punjab (north east), Khyber Paktunkhwa
(north west) and Sindh (south east), NO2 columns are maximum in winter
and minimum in summer months while a reversed seasonality was observed
in the province of Baluchistan (south west). We compared the observed
spatio-temporal patterns to existing emission inventories and found that
for the most populated provinces the NOx emissions are clearly dominated
by anthropogenic sources. In these areas also the strongest positive
trends were observed. NOx released from soils and produced by lightning
both together contribute about 20% for the provinces of Punjab, Sindh,
and Khyber Paktunkhwa, while its contribution in Baluchistan is much
stronger (similar to 50%). NOx emissions from biomass burning are
negligible. This finding can also explain the observed summer maximum in
Baluchistan, since the highet lightning activity occurs during the
Monsoon season. Our comparison also indicates that the inventories of
anthropogenic NOx emissions over Pakistan seem to underestimate the true
emissions by about a factor of two.
