3 Min Read ROME (Thomson Reuters Foundation) - Lockdowns during the first wave of COVID-19 had a much smaller impact on urban air quality than first expected, a study of 11 global cities, from Wuhan to New York, found on Wednesday. As millions stayed home, concentrations in the air of nitrogen dioxide (NO2) - a key pollutant emitted by traffic, linked to respiratory infections and cancer - fell by between 10% and 50%, said the paper in the journal Science Advances. But at the same time, concentrations of ozone (O3) - which can cause chest pain, harm lung tissue and worsen asthma - increased by 2% to 30% in different cities, scientists found after accouting for the impact of weather and seasonal trends.