CO levels showed the most significant reductions during the partial lockdown.• NO 2 decreased in a lower extent, due to industrial and diesel input. • PM 10 levels were only reduced during the first partial lockout week. • Ozone increased due to the decrease in nitrogen oxides level in a VOCcontrolled scenario.

Primary atmospheric pollutant concentrations decreased during the lockdown. • Ozone levels increased during lockdown in many cities of the world. • Ozone levels were related to the increase in NMHC/NO x ratios in a VOCcontrolled scenario. • Air masses from the industrial areas contributed to ozone increase.

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