Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Global to local impacts on atmospheric CO2 caused by COVID-19 lockdown   The world-wide lockdown in response to the COVID-19 pandemic in year 2020 led
to economic slowdown and large reduction of fossil fuel CO2 emissions, but it
is unclear how much it would reduce atmospheric CO2 concentration, and whether
it can be observed. We estimated that a 7.9% reduction in emissions for 4
months would result in a 0.25 ppm decrease in the Northern Hemisphere CO2, an
increment that is within the capability of current CO2 analyzers, but is a few
times smaller than natural CO2 variabilities caused by weather and the
biosphere such as El Nino. We used a state-of-the-art atmospheric transport
model to simulate CO2, driven by a new daily fossil fuel emissions dataset and
hourly biospheric fluxes from a carbon cycle model forced with observed climate
variability. Our results show a 0.13 ppm decrease in atmospheric column CO2
anomaly averaged over 50S-50N for the period February-April 2020 relative to a
10-year climatology. A similar decrease was observed by the carbon satellite
GOSAT3. Using model sensitivity experiments, we further found that COVID, the
biosphere and weather contributed 54%, 23%, and 23% respectively. This
seemingly small change stands out as the largest sub-annual anomaly in the last
10 years. Measurements from global ground stations were analyzed. At city
scale, on-road CO2 enhancement measured in Beijing shows reduction of 20-30
ppm, consistent with drastically reduced traffic during the lockdown. The
ability of our current carbon monitoring systems in detecting the small and
short-lasting COVID signal on the background of fossil fuel CO2 accumulated
over the last two centuries is encouraging. The COVID-19 pandemic is an
unintended experiment whose impact suggests that to keep atmospheric CO2 at a
climate-safe level will require sustained effort of similar magnitude and
improved accuracy and expanded spatiotemporal coverage of our monitoring
systems.

25
The categories of this paper are: patt-sol
20
The categories of this paper are: acc-phys
21
The categories of this paper are: adap-org
23
The categories of this paper are: solv-int
26
The categories of this paper are: bayes-an
14
The categories of this paper are: math-ph
12
The categories of this paper are: nucl-th
31
The categories of this paper are: ao-sci
28
The categories of this paper are: alg-geom
18
The categories of this paper are: econ
5
The categories of this paper are: gr-qc
1
The categories of this paper are: cs
34
The categories of this paper are: chem-ph
33
The categories of this paper are: plasm-ph
16
The categories of this paper are: stat
19
The categories of this paper are: eess