District with the other regions, and bears the greatest contribution
of vehicle emissions. The possible pollution factor
for the region including the northern area of Xigu District
and eastern area of Chengguan District is industrial pollution,
and that in the region of narrowest section is caused by
vehicle emissions. These results are concordant with those
of other studies regarding the spatial variation of magnetic
characteristics of street dust in Lanzhou. At the same time,
Wang et al. [23,24] and Xia et al. [19,20] consider that the
temporal variation on the street dust and dustfall show that
despite the fact that pollution in winter and spring is still
higher than in summer, in recent years, winter pollution has
been gradually reducing, and summer pollution has shown
little change. A visible change in the source of pollution in
Lanzhou City shows a trend of shifting from “coal-burning”
to “vehicles + industry”.