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A response to: Thurston, G.D., Chen, L.C., Campen, M. (2022). Particle toxicity’s role in air pollution. Science, 375(6580), 506-506.

Fine particulate matter (PM2.5, particles with a mass median aerodynamic diameter of less than 2.5 micrometers) in the atmosphere is associated with severe negative impacts on human health, and the gases sulfur dioxide, nitrogen oxides, and ammonia are the main PM2.5 precursors. However, their contribution to global health impacts has not yet been analyzed. Here, we show that nitrogen accounted for 39% of global PM2.5 exposure in 2013, increasing from 30% in 1990 with rising reactive nitrogen emissions and successful controls on sulfur dioxide. Nitrogen emissions to air caused an estimated 23.3 million years of life lost in 2013, corresponding to an annual welfare loss of 420 billion United States dollars for premature death. The marginal abatement cost of ammonia emission is only 10% that of nitrogen oxides emission globally, highlighting the priority for ammonia reduction.

Source apportionment and the effect of reducing individual sources is important input for the development of strategies to address air pollution. The UK Integrated Assessment Model, UKIAM, has been developed for this purpose as a flexible framework, combining information from different atmospheric dispersion models to cover different pollutant contributions, and span the range from European to local scale. In this paper we describe the UKIAM as developed for SO2, NOx, NH3, PM2.5 and VOCs. We illustrate its versatility and application with assessment of current PM2.5 concentrations and exposure of the UK population, as a case-study that has been used as the starting point to investigate potential improvement towards attainment of the WHO guideline of 10 µg/m3.

Air pollution presents a major risk to human health, resulting in premature deaths and reduced quality of life. Quantifying the role of vegetation in reducing air pollution concentrations is an important contribution to urban natural capital accounting. However, most current methods to calculate pollution removal are static, and do not represent atmospheric transport of pollutants, or interactions among pollutants and meteorology. An additional challenge is defining urban extent in a way that captures the green and blue infrastructure providing the service in a consistent way. We developed a refined urban morphology layer which incorporates urban green and blue space. We then applied an atmospheric chemistry transport model (EMEP4UK) to calculate pollutant removal by urban natural capital for pollutants including PM2.5, NO2, SO2, O3. We calculated health benefits directly from the change in pollutant concentrations (i.e. exposure) rather than from tonnes of pollutant removed. Urban natural capital across Britain removes 28,700 tonnes of PM2.5, NO2, SO2, O3. The economic value of the health benefits are substantial: £136 million in 2015, resulting from 900 fewer respiratory hospital admissions, 220 fewer cardiovascular hospital admissions, 240 fewer deaths and 3600 fewer Life Years Lost.

Air pollution presents a major risk to human health, resulting in premature deaths and reduced quality of life. Vegetation can play a role in reducing concentrations of air pollutants, but estimates of the service that vegetation provides are highly variable. The majority of methods used to calculate pollution removal are driven with static concentrations and therefore ignore the feedback of removal on concentrations, and interactions with wet deposition processes and between compounds. In this study we applied an atmospheric chemistry and transport model (EMEP4UK) to calculate the amount of pollutant removal in the UK by current vegetation for PM2.5, but also gaseous pollutants (NO2, NH3, SO2, O3) by comparing a model run with current landcover to a baseline scenario in which vegetation was replaced by bare soil. From these data we calculated the health benefits from the changes in pollutant concentrations (i.e. change in exposure) induced by the additional pollution removal by the vegetation. Results show that current UK vegetation as a whole reduces concentrations of PM2.5 by around 10%, far greater than in previous studies. The economic value of the health benefits are substantial: £1 billion in avoided health costs estimated for 2015, resulting from 1900 avoided deaths, 27,000 avoided life years lost, 5,800 fewer respiratory hospital admissions and 1,300 fewer cardiovascular hospital admissions. We also show that the benefits do not always occur in the same location as the pollutant removal. In other words the benefits, defined in terms of reduced pollutant concentrations, are also transported in the atmosphere. Copyright © 2018 by the International Aerosol Conference (IAC).