FLOWERS become harder to smell for bees, moths and other pollinating insects in polluted air, according to research led by the University of Reading.
Scientists analysed 22 experimental studies on how the air pollutants ozone and nitrogen oxides (NOx) affect pollinators. Both pollutants make it harder for pollinators to find flowers by breaking down or altering the scents that flowers give off.
The new research, published in the journal Frontiers in Ecology and the Environment, found that elevated ozone reduced pollinator performance by an average of 42%, while NOx cut performance by 46%. When the two pollutants occurred together, the average reduction was 68%.
Only a few studies tested both pollutants together, and in those the extra harm from combining them was smaller than the averages suggest.
This is because the two gases react with each other in the air and partly cancel each other out.
Diesel vehicles produce most NOx pollution and can stay on roads for more than 20 years after the last new one is sold.
The UK’s delayed ban on new petrol and diesel cars, pushed from 2030 to 2035 risks extending the damage to pollinators.
The study also found that specialist pollinators reliant on one plant’s scent, such as some moths, are more at risk than generalists like many bees.
It also discovered that day-active pollinators such as bees and butterflies face higher ozone levels, while night-active pollinators (including many moths) encounter higher nitrogen oxides.
Dr James Ryalls, lead author of the study at the University of Reading, said: “Ozone levels are projected to keep rising until around 2050, even as NOx emissions begin to fall as the world moves away from fossil fuels.
This creates a difficult period for pollinators over the next two-to-three decades. Once cleaner fuels take over fully, ozone levels should decline, giving pollinators a chance to recover.
“How quickly that recovery happens depends on the choices governments make now. Cutting NOx emissions faster, especially from diesel vehicles, could shorten the difficult period and speed up recovery.
“Most of the food we grow depends on healthy pollinators, so protecting them from pollution cannot wait until 2050.”
