Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Temporal and spatial correlation patterns of air pollutants in Chinese
  cities   As a huge threat to the public health, China's air pollution has attracted
extensive attention and continues to grow in tandem with the economy. Although
the real-time air quality report can be utilized to update our knowledge on air
quality, questions about how pollutants evolve across time and how pollutants
are spatially correlated still remain a puzzle. In view of this point, we adopt
the PMFG network method to analyze the six pollutants' hourly data in 350
Chinese cities in an attempt to find out how these pollutants are correlated
temporally and spatially. In terms of time dimension, the results indicate
that, except for O$_3$, the pollutants have a common feature of the strong
intraday patterns of which the daily variations are composed of two contraction
periods and two expansion periods. Besides, all the time series of the six
pollutants possess strong long-term correlations, and this temporal memory
effect helps to explain why smoggy days are always followed by one after
another. In terms of space dimension, the correlation structure shows that
O$_3$ is characterized by the highest spatial connections. The PMFGs reveal the
relationship between this spatial correlation and provincial administrative
divisions by filtering the hierarchical structure in the correlation matrix and
refining the cliques as the tinny spatial clusters. Finally, we check the
stability of the correlation structure and conclude that, except for PM$_{10}$
and O$_3$, the other pollutants have an overall stable correlation, and all
pollutants have a slight trend to become more divergent in space. These results
not only enhance our understanding of the air pollutants' evolutionary process,
but also shed lights on the application of complex network methods into
geographic issues.

10
The categories of this paper are: q-bio
11
The categories of this paper are: hep-lat
22
The categories of this paper are: chao-dyn
25
The categories of this paper are: patt-sol
16
The categories of this paper are: stat
1
The categories of this paper are: cs
31
The categories of this paper are: ao-sci
26
The categories of this paper are: bayes-an
17
The categories of this paper are: q-fin
19
The categories of this paper are: eess
4
The categories of this paper are: cond-mat
6
The categories of this paper are: astro-ph
33
The categories of this paper are: plasm-ph
20
The categories of this paper are: acc-phys
35
The categories of this paper are: mtrl-th
2
The categories of this paper are: math