## 3 Results  
Figure 2 shows the monthly emissions of analyzed pollutants for the compared periods. In the first half of 2020, the emissions of the four groups of pollutants associated with road transportation decreased starting in March compared with those estimated for the base year 2018. In late March 2020, the national government adopted vehicle restrictions, so April showed a higher reduction of GHG emissions for CO\({}_{2}\), CH\({}_{4}\) and N\({}_{2}\)O in percentages equivalent to 58%, 40% and 71%, respectively. CO\({}_{2}\) reduction was the most representative due its contribution of 97.62% of the total emissions from the transport sector, specifically the burning of fossil fuels by road transportation (lightweight and cargo vehicles) [38]. Later, GHG emissions increased in May by 24%, 16% and 27% for CO\({}_{2}\), CH\({}_{4}\) and N\({}_{2}\)O, respectively, owing the reactivation of some economic sectors. Restrictions began to be relaxed, allowing the opening of some activities that were restricted during the confinement. As a result, GHG emissions in June continued to increase, though they remained lower than those of 2018. As shown in Figure 3, all estimated pollutants showed reductions between January and June 2020 due to the pandemic lockdown in Colombia. Negative variations in GHG emissions were 28%, 17% and 20% for CO\({}_{2}\), N\({}_{2}\)O and CH\({}_{4}\), respectively. While the ozone precursor group showed a reduction of up to 21% and 22% for CO and NMVOC, respectively. The emissions of these pollutants were mostly the result of burning gasoline and diesel oil, which represent 90% of the total emissions. In addition, the NOx emissions variation was \(-\)15% for the study period, with 50% of the total emissions by this pollutant attributed to the burning of diesel oil. Aerosol emissions of PM\({}_{10}\) and PM\({}_{2.5}\) each showed a negative emissions variation of 17%, which was associated mostly with the fuel consumption by cargo vehicles and public transport [57]. BC emissions showed a decrease of 15%, and acidifying gases also displayed reductions. SO\({}_{2}\) emissions showed a negative variation of 19%, while NH\({}_{3}\) emissions were reduced by 23% of its. These emissions reductions were mainly produced by the reduction in consumption of gasoline and diesel oil. In general, pollutant groups that registered the most reduction in emissions variations were GHGs (\(-\)22%) and acidifying gases (\(-\)21%), while CO\({}_{2}\) presented the greatest reduction among all pollutants analyzed. Figure 2: Estimated total emissions (Gg) of the four groups of pollutants that affect climate change, air quality and health: (**a**) GHGs (CH\({}_{4}\), CO\({}_{2}\) and N\({}_{2}\)O); (**b**) ozone precursors (CO, NMCOV and NOx); (**c**) aerosols (BC, PM\({}_{10}\) and PM\({}_{2.5}\)); (**d**) acidifying gases (NH\({}_{3}\) and SO\({}_{2}\)) for January to June of 2018 and 2020. Figure 4 shows the variations in CO\({}_{2}\) emissions in Colombia. Territorial divisions that showed the greatest reduction in CO\({}_{2}\) emissions were Bogota D.C. (\(-\)4168 Gg CO\({}_{2}\)), Magdalena (\(-\)1381 Gg CO\({}_{2}\)), Bolivar (\(-\)308 Gg CO\({}_{2}\)), Atlantico (\(-\)118 Gg CO\({}_{2}\)), and Caqueta (\(-\)30 Gg CO\({}_{2}\)). These contrast with positive emission variations in departments such as Valle del Cauca (295 Gg CO\({}_{2}\)), Cundinamarca (278 Gg CO\({}_{2}\)), Norte de Santander (248 Gg CO\({}_{2}\)), Antiquia (232 Gg CO\({}_{2}\)), and Cesar (209 Gg CO\({}_{2}\)), during the study period. Colombian administrative divisions that showed the greatest reduction in CO\({}_{2}\) (Bogota, Magdalena, Bolivar, Atlantico and Caqueta) make up 44.5% of the national population. The circulation of people was reduced to avoid contagion by COVID-19. Thus, these territories registered (between March and June 2020) a decrease of 6005 Gg of CO\({}_{2}\) compared to the same period in 2018.