Symbol	Description
NO2	Nitrogen dioxide
SO2	Sulphur dioxide
CO	Carbon monoxide
PM2.5	Particle matter under 2.5 microns diameter
PM10	Particle matter under 10 microns diameter
NASA	The National Aeronautics and Space Administration
COVID-19	Coronavirus Disease 2019
SARS-CoV-2	Severe acute respiratory syndrome coronavirus 2
WHO	World Health Organization
N95 masks	Respirators that filter out 95 percent of airborne particles
EPA	United States Environmental Protection Agency
PPB	Parts per billion
OCO2	NASA Orbiting Carbon Observatory 2 product
CAMS	Copernicus Atmosphere Monitoring Service
ERA5 satellite	The fifth generation ECMWF atmospheric reanalysis of the global climate
NACE rev. 2	Statistical classification of economic activities in the European Community
US EPA standard	United States Environmental Protection Agency data standards
NAAQS	National ambient air quality standard
IP	Air pollution score for each pollutant
CP	The period average truncated concentration for each pollutant
BPHi	The concentration breakpoint first to exceed the CP
BPLo	The concentration breakpoint first below the CP
IHi	The AQI values corresponding to BPHi
ILo	The AQI values corresponding to BPLo
ARX	Autoregressive model with exogenous input
APIchange	Air pollution index changes
APIperiod y (X)	The air pollution index for each of the three periods: 1 March–30 May, 1 June–30 August and 1 September–30 October
X	Each country taken into consideration
P	Pollutant
US	United States
PPM	Parts per million
NetCDF	Network Common Data Form