NO2 and dust Classic for local to regional up-scaling

Air pollution in the industrialized world has undergone drastic changes in the past 50 years (Table 2.73). Until World War II the most important urban compound was sulfur dioxide combined with soot from the use of fossil fuels in heat and 

When that problem was partly solved by cleaner fuels, higher stacks and flue-gas cleaning in urban areas, the growing traffic gave rise to nitrogen oxides and VOCs and in some areas photochemical air pollution, which can be abated by catalytic converters. Lately, interest has centered on small particles and more exotic organic compounds that can be detected with new sophisticated analytical techniques. 

Dust concentrations in the air were previously larger factors than nowadays. Large global differences still were observed but only on a local scale, in other words influenced by local (primary) dust sources. Fig. 2.64 shows an example on longterm PMio monitoring at two sites in eastern Germany. The decrease by a factor of more than two between 1989 and 1999 is because of reduced flue-ash emissions and the introduction of desulfurization in coal-fired power stations in this period. 

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