By Robert Preidt HealthDay Reporter

WEDNESDAY, Jan. 13, 2021 (HealthDay News) -- Two types of air pollution declined in cities around the world during initial COVID-19 lockdowns, but one type increased, a new study finds.

Researchers assessed changes in levels of nitrogen dioxide, ozone and fine particulate (PM2.5) air pollution during lockdowns in 11 cities: Beijing and Wuhan in China; Milan; Rome; Madrid; London; Paris; Berlin; New York; Los Angeles; and Delhi, India.

After accounting for weather effects, the researchers found that reductions in nitrogen dioxide were smaller than anticipated, while ozone concentrations rose.

Nitrogen dioxide is a major air pollutant from vehicle emissions, and is associated with respiratory problems. Ozone is also harmful to health and damages crops, the study authors noted.