The health burden of air pollution in the UK: a modelling study using updated exposure-risk associations.

BACKGROUND: Long-term exposure to ambient air pollution, in particular fine particles or PM2·5, is a leading global disease burden. PM2·5 in the UK, dominated by agricultural emissions of ammonia (NH3), 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 PM2·5 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. METHODS: For this modelling study, we used the GEOS-Chem model nested over the UK to simulate ambient PM2·5 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 PM2·5 and risk for PM2·5 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. FINDINGS: We estimated that adult premature mortality attributable to exposure to ambient PM2·5 in the UK totalled 48 625 deaths in 2019 (95% CI 45 118-52 595); 15 000-20 000 more deaths than those estimated using outdated health-risk assessment models.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). INTERPRETATION: According to our findings, PM2·5 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 PM2·5, in particular the unregulated agricultural sector. FUNDING: Department for the Environment, Food and Rural Affairs (DEFRA).

Impact of Legislated and Best Available Emission Control Measures on UK Particulate Matter Pollution, Premature Mortality, and Nitrogen-Sensitive Habitats.

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.

Abrupt but smaller than expected changes in surface air quality attributable to COVID-19 lockdowns.

The COVID-19 lockdowns led to major reductions in air pollutant emissions. Here, we quantitatively evaluate changes in ambient NO2, O3, and PM2.5 concentrations arising from these emission changes in 11 cities globally by applying a deweathering machine learning technique. Sudden decreases in deweathered NO2 concentrations and increases in O3 were observed in almost all cities. However, the decline in NO2 concentrations attributable to the lockdowns was not as large as expected, at reductions of 10 to 50%. Accordingly, O3 increased by 2 to 30% (except for London), the total gaseous oxidant (O x = NO2 + O3) showed limited change, and PM2.5 concentrations decreased in most cities studied but increased in London and Paris. Our results demonstrate the need for a sophisticated analysis to quantify air quality impacts of interventions and indicate that true air quality improvements were notably more limited than some earlier reports or observational data suggested.

Chemistry of Atmospheric Fine Particles During the COVID-19 Pandemic in a Megacity of Eastern China.

Air pollution in megacities represents one of the greatest environmental challenges. Our observed results show that the dramatic NOx decrease (77%) led to significant O3 increases (a factor of 2) during the COVID-19 lockdown in megacity Hangzhou, China. Model simulations further demonstrate large increases of daytime OH and HO2 radicals and nighttime NO3 radical, which can promote the gas-phase reaction and nocturnal multiphase chemistry. Therefore, enhanced NO3 - and SO4 2- formation was observed during the COVID-19 lockdown because of the enhanced oxidizing capacity. The PM2.5 decrease was only partially offset by enhanced aerosol formation with its reduction reaching 50%. In particular, NO3 - decreased largely by 68%. PM2.5 chemical analysis reveals that vehicular emissions mainly contributed to PM2.5 under normal conditions in Hangzhou. Whereas, stationary sources dominated the residual PM2.5 during the COVID-19 lockdown. This study provides evidence that large reductions in vehicular emissions can effectively mitigate air pollution in megacities.

Variation in Concentration and Sources of Black Carbon in a Megacity of China During the COVID-19 Pandemic.

Black carbon (BC) not only warms the atmosphere but also affects human health. The nationwide lockdown due to the Coronavirus Disease 2019 (COVID-19) pandemic led to a major reduction in human activity during the past 30 years. Here, the concentration of BC in the urban, urban-industry, suburb, and rural areas of a megacity Hangzhou were monitored using a multiwavelength Aethalometer to estimate the impact of the COVID-19 lockdown on BC emissions. The citywide BC decreased by 44% from 2.30 to 1.29 µg/m3 following the COVID-19 lockdown period. The source apportionment based on the Aethalometer model shows that vehicle emission reduction responded to BC decline in the urban area and biomass burning in rural areas around the megacity had a regional contribution of BC. We highlight that the emission controls of vehicles in urban areas and biomass burning in rural areas should be more efficient in reducing BC in the megacity Hangzhou.