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Past emission controls in the UK have substantially reduced precursor emissions of health‐hazardous fine particles (PM2.5) and nitrogen pollution detrimental to ecosystems. Still, 79% of the UK exceeds the World Health Organization (WHO) guideline for annual mean PM2.5 of 5 μg m−3 and there is no enforcement of controls on agricultural sources of ammonia (NH3). NH3 is a phytotoxin and an increasingly large contributor to PM2.5 and nitrogen deposited to sensitive habitats. Here we use emissions projections, the GEOS‐Chem model, high‐resolution data sets, and contemporary exposure‐risk relationships to assess potential human and ecosystem health co‐benefits in 2030 relative to the present day of adopting legislated or best available emission control measures. We estimate that present‐day annual adult premature mortality attributable to exposure to PM2.5 is 48,625 (95% confidence interval: 45,188–52,595), that harmful amounts of reactive nitrogen deposit to almost all (95%) sensitive habitat areas, and that 75% of ambient NH3 exceeds levels safe for bryophytes and lichens. Legal measures decrease the extent of the UK above the WHO guideline to 58% and avoid 6,800 premature deaths by 2030. This improves with best available measures to 36% of the UK and 13,300 avoided deaths. Both legal and best available measures are insufficient at reducing the extent of damage of nitrogen pollution to sensitive habitats. Far more ambitious reductions in nitrogen emissions (>80%) than is achievable with best available measures (34%) are required to halve the amount of excess nitrogen deposited to sensitive habitats. Plain Language Summary: Particulate matter pollution is detrimental to human health, nitrogen pollution offsets ecosystem balance of sensitive habitats, and ammonia is toxic to plants. Here we determine the potential public health and ecosystem benefits of adopting currently legislated or best available emission control measures. We use state‐of‐science air quality and exposure assessment models and high‐resolution data sets to estimate air pollution abundances and deposition and determine risk of human and ecosystem harm from air pollution in the UK. We find that substantial improvements to public health result from currently legislated measures, estimated as the number of avoided early deaths attributable to decline in particulate matter pollution. The number of avoided deaths doubles with best available emission control measures, as these also target particulate matter precursor emissions of ammonia from agricultural activity not mandated by existing legislation. The benefits to sensitive habitats of either legal or best available measures is near‐negligible. Mitigating harm to ecosystems will require major advances in emission mitigation technologies. Key Points: Efficacy of required and best available emission control technologies tested with the GEOS‐Chem model and new exposure‐harm relationshipsBoth reduce public exposure to particulate matter pollution and avoid 6,800 adult early deaths with legislation and 13,300 with technologyNeither is sufficient at lessening sensitive habitat exposure to harmful loads of nitrogen and concentrations of phytotoxic ammonia [ABSTRACT FROM AUTHOR]

Long-term exposure to ambient air pollution, in particular fine particles or PM 2·5 , is a leading global disease burden. PM 2·5 in the UK, dominated by agricultural emissions of ammonia (NH 3), has been estimated to be responsible for 29 000–34 000 adult early deaths a year. These estimates use models that relate exposure to health risk that predate cohort studies that have identified a supralinear relationship between exposure and risk at relatively low PM 2·5 concentrations typical of the UK (5–12 mg m−3). Here we used this new knowledge to estimate adult premature mortality in the UK in 2019. For this modelling study, we used the GEOS-Chem model nested over the UK to simulate ambient PM 2·5 concentrations, UK Office for National Statistics (ONS) health data provided by the Global Burden of Disease (GBD), and a hybrid health-risk assessment model. The hybrid model fuses a well established linear relationship between PM 2·5 and risk for PM 2·5 exceeding 10 mg m−3 with a supralinear curve at lower concentrations that is constrained with cohort studies conducted in Canada and confirmed with similar relationships from cohort studies in the USA and Europe. We estimated that adult premature mortality attributable to exposure to ambient PM 2·5 in the UK totalled 48 625 deaths in 2019 (95% CI 45 118–52 595); 15 000–20 000 more deaths than those estimated using outdated health-risk assessment models. Older people (aged 65 years or older) account for most UK deaths (86%). All adult premature mortality (in people aged 25 years and older) in Greater London (4861, 95% CI 4549–5247) exceeded that in Scotland (3673, 3214–4073), Wales (2462, 2270–2660), and Northern Ireland (1052, 934–1156). According to our findings, PM 2·5 is more hazardous to UK adults than previously reported, but a supralinear exposure-response curve also suggests that there are substantial public health gains in targeting dominant source contributors to PM 2·5 , in particular the unregulated agricultural sector. Department for the Environment, Food and Rural Affairs (DEFRA). [ABSTRACT FROM AUTHOR]