5.2  Global analysis
Making a global balance of the analyzed countries, the variation of the PM2.5 concentration had an average reduction of 12%. The highest reduction occurs in the African continent with one (1) country analyzed (33%), followed by the American continent (22%) and the Asian continent (16%); finally, the European continent, in which a favorable reduction result is not generally observed (5%). Fig. 7 shows the PM2.5 variation in a global map of capital cities. The absolute value of the variation can be identified by size of the circle. In red we find the cities with increases in their PM2.5 measurement and in pink the cities with PM2.5 reduction, the city with the greatest PM2.5 reduction within the data collected is Bogota, with a reduction of 57% compared to a typical week.
Fig. 7 PM2.5 Reduction in quarantine week.
Fig. 8 shows in detail the PM2.5 quantitative variation of the analyzed cities, as well as its mean concentration. The gray color represents the PM2.5 behavior under typical conditions, and the light blue color represents the confinement mode. Dhaka, the most polluted capital of this particulate matter, had a 14% reduction. It is observed as the first seventeen (17) most contaminated capitals in the world, from Dhaka, to Skopje, exceed the PM2.5 average concentrations (75.78 μg/m3) from before quarantine, maintaining an AQI level from moderate to unhealthy. Likewise, during typical times twelve (12) countries present an AQI level below the quarantine average (Bern - Kyiv) almost all with a good AQI level. During the quarantine, sixteen (16) capitals exceed the PM2.5 registered average (66.92%), equivalent to a moderate AQI level, and nine (9) cities registered a good AQI level. Specifically, the three most polluted capital cities that are Dhaka, followed by Kampala and Delhi, reduced their PM2.5 concentration by 14%, 35% and 40% respectively. The capital city with the highest PM2.5 reduction during quarantine was Bogotá, with a percentage of 57%, going from a moderate to a good AQI level. Kubait City, presents the second largest PM2.5 reduction (42%). Finally, with reductions over 40%, there are the cities of Delhi and Tehran.
Fig. 8 Weekly average without quarantine vs weekly average with quarantine.
In Europe, the continent with the best environmental conditions in normal times, a very high increase in PM2.5 is observed in the cities of Prague, Vienna and Bratislava, cities very close to each other; apparently, an isolated effect produced by winds or fires.