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Bees and other pollinators find flowers partly by smell, and ozone and nitrogen oxides (NOx) can chemically alter the scent compounds flowers release. In controlled tests, bees recognized or were attracted to altered floral scents less often. A October 2026 University of Reading news release summarizing 22 experimental studies reported average pollinator-performance reductions of 42% under elevated ozone, 46% under NOx, and 68% where both pollutants were present together. The combined figure needs careful reading, because only a few studies tested the two pollutants together, and the extra harm they found was smaller than the averages suggest.
Why air pollution interferes with a flower’s scent
A flower’s smell is not one chemical. It is a blend of volatile organic compounds, and a pollinator learns the specific mix of a flower it has visited before. Pollinators detect that blend and use it to choose which flowers to approach.
Ozone and NOx are reactive. When they meet floral volatiles in the air, they can break those compounds down or change their chemistry. The result is not simply a weaker smell or a smell hidden under other odors. The blend itself can change, so a bee that learned the original pattern may no longer match it to the flower.
What the 2026 review found
The University of Reading summary combined results from 22 experimental studies. Its averages were:
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- Elevated ozone: an average 42% reduction in pollinator performance.
- NOx: an average 46% reduction.
- Ozone and NOx together: an average 68% reduction.
These are averages across studies that measured different things under different conditions, so they are not a single measured effect. Only a few of the 22 studies tested both pollutants together. Those studies found the additional harm from the combination was smaller than the averages imply, because the two gases react with each other in the air and partly cancel out. The combined exposure should therefore not be read as the sum of the single-pollutant effects. The summary also notes that specialist pollinators that depend on one plant’s scent may be more at risk than generalist species that visit many plants.
Evidence from controlled scent tests
Oilseed rape blend and diesel exhaust (2013)
In a 2013 controlled experiment, researchers exposed a synthetic blend of eight floral chemicals, based on those identified from oilseed rape, to diesel exhaust. Within one minute, four of the chemicals fell significantly and two became undetectable. Honeybees trained on the original blend recognized the altered blend less well. The study identified the NOx fraction of the exhaust as a key driver of the change at environmentally relevant levels.
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Black mustard and buff-tailed bumblebees (ozone)
A study of black mustard (Brassica nigra) found that ozone changed the relative composition of the flower’s scent and reduced its attractiveness to buff-tailed bumblebees (Bombus terrestris). The exposure reported was 120 ppb ozone over 4.5 m.
Ozone plume experiment (2023)
A 2023 study of an ozone plume measured how often honeybees recognized a floral blend. For the plume-centre blend, recognition was 52% at 6 m and 38% at 12 m. For the more degraded plume-edge blend, recognition fell to 32% at 6 m and 10% at 12 m. The pattern shows that the more the blend is altered, the less reliably bees recognize it.
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Evidence from field experiments
Lab recognition tests isolate the scent effect, but they do not show what happens to a whole pollinator community. Field studies do.
Field fumigation with diesel exhaust and ozone (2022)
A 2022 Environmental Pollution study fumigated plots of a self-fertile test plant with elevated diesel exhaust and/or ozone. The treatments were described as below the air-quality standards in force at the time. The study reported 62–70% fewer locally occurring wild and managed pollinators, 83–90% fewer flower visits, and 14–31% reductions across three pollination and yield measures for the test plant.
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Two-summer field-scale study
A separate field-scale study ran over two summers and reported pollinator abundance reductions of up to 48% under ozone and diesel exhaust exposure. The adverse effects appeared when flowers were available, which is consistent with flowers’ own scent cues playing a role.
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How the studies compare
The studies measured different outcomes, so their percentages should not be compared directly.
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| Study | Pollutant or exposure | Design | Outcome measured | Reported result |
|---|---|---|---|---|
| University of Reading synthesis (2026), 22 studies | Ozone; NOx; both together | Pooled experimental studies | Pollinator performance | Average 42% (ozone), 46% (NOx), 68% (both); combined harm smaller than averages suggest |
| Oilseed rape blend study (2013) | Diesel exhaust, NOx fraction | Controlled chemical and honeybee recognition test | Blend composition; recognition | Four chemicals fell significantly, two undetectable within one minute; recognition reduced |
| Black mustard study | Ozone at 120 ppb over 4.5 m | Controlled scent and bumblebee attraction | Scent composition; attractiveness | Composition changed; attractiveness reduced |
| Ozone plume study (2023) | Ozone plume | Honeybee recognition test | Recognition of floral blend | Plume-centre: 52% (6 m), 38% (12 m); plume-edge: 32% (6 m), 10% (12 m) |
| Field fumigation (2022) | Diesel exhaust and/or ozone, below then-current standards | Field fumigation of a self-fertile test plant | Pollinator numbers; flower visits; pollination and yield | 62–70% fewer pollinators; 83–90% fewer visits; 14–31% reductions in three pollination/yield measures |
| Two-summer field study | Ozone and diesel exhaust | Field-scale exposure over two summers | Pollinator abundance | Up to 48% reduction; effects when flowers were available |
What the evidence does and does not show
- It shows a mechanism. Ozone and NOx can alter the scent blend that pollinators use to find and recognize flowers, and controlled tests have measured this change and the drop in recognition or attraction that follows.
- It shows field effects under experimental exposure. The 2022 and two-summer field studies recorded fewer pollinators and visits under the pollution treatments.
- It does not give one number for all bees. The effects differ by species, by flower, and by how many pollutants are present. Specialist pollinators may be more exposed than generalists.
- It does not establish a global crop-yield figure. The field study yield measures came from one self-fertile test plant. They do not by themselves quantify crop losses or food-supply effects across farming systems.
In short, the evidence supports concern about pollinator foraging under air pollution, and it identifies scent disruption as a plausible route. The sizes of the effects depend on the pollutant, the species, and the test design, and no single percentage captures them.
The combined-pollutant question remains the least settled part of the picture. The averages suggest a larger effect when ozone and NOx occur together, but the studies that tested the mixture found that the extra harm was smaller than adding the single-pollutant averages would predict.
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