moreover a increase in the share of agriculture in value added is associated with an increase of in so concentration in contrast to other pollutants the degree of fragmentation of an urban area does not appear to affect so concentration this might be due to the fact that so is mainly produced by energy generation processes rather than by road transportation in particular this study presents evidence that urban fragmentation is correlated with higher concentrations of no and pm when controlling for economic factors and climate conditions moreover the results suggest that densely populated urban areas are associated with higher so concentrations