Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Effects of the COVID-19 lockdown on urban light emissions: ground and
  satellite comparison   'Lockdown' periods in response to COVID-19 have provided a unique opportunity
to study the impacts of economic activity on environmental pollution (e.g.
NO$_2$, aerosols, noise, light). The effects on NO$_2$ and aerosols have been
very noticeable and readily demonstrated, but that on light pollution has
proven challenging to determine. The main reason for this difficulty is that
the primary source of nighttime satellite imagery of the earth is the
SNPP-VIIRS/DNB instrument, which acquires data late at night after most human
nocturnal activity has already occurred and much associated lighting has been
turned off. Here, to analyze the effect of lockdown on urban light emissions,
we use ground and satellite data for Granada, Spain, during the COVID-19
induced confinement of the city's population from March 14 until May 31, 2020.
We find a clear decrease in light pollution due both to a decrease in light
emissions from the city and to a decrease in anthropogenic aerosol content in
the atmosphere which resulted in less light being scattered. A clear
correlation between the abundance of PM10 particles and sky brightness is
observed, such that the more polluted the atmosphere the brighter the urban
night sky. An empirical expression is determined that relates PM10 particle
abundance and sky brightness at three different wavelength bands.

20
The categories of this paper are: acc-phys
5
The categories of this paper are: gr-qc
34
The categories of this paper are: chem-ph
33
The categories of this paper are: plasm-ph
28
The categories of this paper are: alg-geom
32
The categories of this paper are: atom-ph
0
The categories of this paper are: hep-ph
35
The categories of this paper are: mtrl-th
23
The categories of this paper are: solv-int
11
The categories of this paper are: hep-lat
37
The categories of this paper are: supr-con
12
The categories of this paper are: nucl-th
22
The categories of this paper are: chao-dyn
13
The categories of this paper are: quant-ph
36
The categories of this paper are: cmp-lg
19
The categories of this paper are: eess