GENEVA (AP) — The U.N. weather agency says the world — and especially urban areas — experienced a brief, sharp drop in emissions of air pollutants last year amid lockdown measures and related travel restrictions put in place over the coronavirus pandemic.

The World Meteorological Organization, releasing its first ever Air Quality and Climate Bulletin on Friday, cautioned that the reductions in pollution were patchy — and many parts of the world showed levels that outpaced air quality guidelines. Some types of pollutants continued to emerge at regular or even higher levels.

"COVID-19 proved to be an unplanned air-quality experiment, and it did lead to temporary localized improvements," said Petteri Taalas, the WMO secretary-general. "But a pandemic is not a substitute for sustained and systematic action to tackle major drivers of both population and climate change and so safeguard the health of both people and planet."

The Geneva-based agency noted an "unprecedented decrease" in pollutant emissions as many governments restricted gatherings, closed schools, and imposed lockdowns.

WMO cited in particular drops of up to nearly 70% in average nitrous oxide levels during full lockdown measures last year, compared to the same periods from 2015 to 2019. But ozone levels, for example, stayed at similar levels or even rose.