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Abstract. We examine the impact of model horizontal resolution on simulated concentrations of surface ozone (O 3 ) and particulate matter less than 2.5 µm in diameter (PM 2.5 ), and the associated health impacts over Europe, using the HadGEM3-UKCA chemistry-climate model to simulate pollutant concentrations at a coarse (∼ 140 km) and a finer (∼ 50 km) resolution. The attributable fraction (AF) of total mortality due to long-term exposure to warm season daily maximum 8 h running mean (MDA8) O 3 and annual-average PM 2.5 concentrations is then calculated for each European country using pollutant concentrations simulated at each resolution. Our results highlight a seasonal variation in simulated O 3 and PM 2.5 differences between the two model resolutions in Europe. Compared to the finer resolution results, simulated European O 3 concentrations at the coarse resolution are higher on average in winter and spring (∼ 10 and ∼ 6 %, respectively). In contrast, simulated O 3 concentrations at the coarse resolution are lower in summer and autumn (∼ −1 and ∼ −4 %, respectively). These differences may be partly explained by differences in nitrogen dioxide (NO 2 ) concentrations simulated at the two resolutions. Compared to O 3 , we find the opposite seasonality in simulated PM 2.5 differences between the two resolutions. In winter and spring, simulated PM 2.5 concentrations are lower at the coarse compared to the finer resolution (∼ −8 and ∼ −6 %, respectively) but higher in summer and autumn (∼ 29 and ∼ 8 %, respectively). Simulated PM 2.5 values are also mostly related to differences in convective rainfall between the two resolutions for all seasons. These differences between the two resolutions exhibit clear spatial patterns for both pollutants that vary by season, and exert a strong influence on country to country variations in estimated AF for the two resolutions. Warm season MDA8 O 3 levels are higher in most of southern Europe, but lower in areas of northern and eastern Europe when simulated at the coarse resolution compared to the finer resolution. Annual-average PM 2.5 concentrations are higher across most of northern and eastern Europe but lower over parts of southwest Europe at the coarse compared to the finer resolution. Across Europe, differences in the AF associated with long-term exposure to population-weighted MDA8 O 3 range between −0.9 and +2.6 % (largest positive differences in southern Europe), while differences in the AF associated with long-term exposure to populationweighted annual mean PM 2.5 range from −4.7 to +2.8 % (largest positive differences in eastern Europe) of the total mortality. Therefore this study, with its unique focus on Europe, demonstrates that health impact assessments calculated using modelled pollutant concentrations, are sensitive to a change in model resolution by up to ∼ ±5 % of the total mortality across Europe.

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The start of 2020 has been characterized by emission reductions in various countries across the globe following the implementation of different lock-down measures to control the transmission of the SARS-CoV-2 (COVID-19). Consequently, these reductions influenced the air quality globally. In this study, we focus on daily nitrogen dioxide (NO2) as well as ozone (O3) concentrations measured across the Maltese Islands between January and mid-October 2020. Changes in air quality are generally difficult to detect due to the complex composition and interactions occurring within the atmosphere. To quantify changes in NO2 and O3 concentrations during the COVID-19 period, we use a random forest machine learning algorithm to determine a business as usual counterfactual scenario. Results highlight a decrease in monthly mean NO2 concentrations by up to 54% in the traffic site of Msida (~21 μg m−3). In contrast, the monthly mean O3 concentrations during the COVID-19 months are up to 61% higher compared to a business as usual scenario in Msida (~28 μg m−3). In this study, we also estimate the differences in attributable fraction (AF) associated with short-term exposure to NO2 and O3 concentrations. In Msida, the AF is up to 0.9% lower and 0.8% higher for measured NO2 and O3 concentrations, respectively. Our results highlight the favorable effects of decreasing traffic-related emissions on NO2 concentrations however, we also note increases in other pollutants for example O3 concentrations which especially in the short-term can lead to various adverse health effects.

In this study we examine the meteorological drivers resulting in concurrent high levels of ozone (O3) and particulate matter smaller than 2.5 µm in diameter (PM2.5) during two five-day air pollution episodes in 2006 (1 st-5 th July and 18 th-22 nd July) using an air quality model (AQUM) at 12 km horizontal resolution to simulate air pollutant concentrations. The resultant UK health burden associated with short-term exposure to simulated maximum daily 8-hour O3 (MDA8 O3) and daily mean PM2.5 is estimated at the national and regional level. Both episodes were found to be driven by anticyclonic conditions with light easterly and south easterly winds and high temperatures that aided pollution build up in the UK. The estimated total mortality burden associated with short-term exposure to MDA8 O3 is similar during the chosen episodes with about 70 daily deaths brought forward (summed across the UK) during the first and second episode, respectively. The estimated health burden associated with short-term exposure to daily mean PM2.5 concentrations differs between the first and second episode resulting in about 43 and 36 daily deaths brought forward, respectively. The corresponding percentage of all-cause mortality due to short-term exposure to MDA8 O3 and daily mean PM2.5 during these two episodes and across the UK regions, ranges from 3.4% to 5.2% and from 1.6% to 3.9%, respectively. The attributable percentage of all-cause mortality differs between the regions depending on the pollution levels in each episode, but the overall estimated health burdens are highest in regions with higher population totals. We estimate that during these episodes the short-term exposure to MDA8 O3 and daily mean PM2.5 is between 36-38% and 39-56% higher, respectively, than if the pollution levels represented typical 2 seasonal-mean concentrations. This highlights the potential of air pollution episodes to have substantial short-term impacts on public health.

Estimating evapotranspiration is crucial for better management of catchment water resources. In this study, the FAO CropWat model was used to estimate reference evapotranspiration (ETo), crop evapotranspiration (ETc), and total gross water requirements for three economically important agricultural crops grown in Malta: potatoes, wheat, and vineyards for three years representative of a typically wet (2003), average (2009), and dry (2013) year. In addition, changes in ETc due to changes in land use were estimated for 2009 and 2013 relative to a 2003 baseline. Across all three years and crops, the average ETo rates were estimated to range between 3.7 mm day -1 (2003) and 4.0 mm day-1 (2013) while average ETc rates were estimated to range between 1.6 mm day-1 and 5.3 mm day-1, respectively. For all three years, the highest total gross water requirement was estimated for wheat, reaching a maximum of 1450 mm in 2013. The results suggest that changes in land use between 2003 and 2013 were the main driver for changes in crop water demand. Differences in water demand compared to 2003 were estimated to range between -38% and 60%. This could have a substantial impact on the future sustainability of Malta’s increasingly constrained water resources.

Abstract.We examine the impact of model horizontal resolution on simulated surface ozone (O3) and particulate matter less 10 than 2.5 μm (PM2.5) concentrations, and the associated health impacts over Europe, using the HadGEM3-UKCA chemistryclimate model to simulate pollutant concentrations over Europe at a global (~ 140 km) and a regional (~ 50 km) resolution.The attributable fraction (AF) of total mortality due to long-term exposure to warm season daily maximum 8-hour running mean (MDA8) O3 and annual-average PM2.5 concentrations is then calculated for each European country using pollutant concentrations simulated at each resolution. Our results highlight a strong seasonal variation in simulated O3 and PM2.5 15 differences between the two model resolutions in Europe. Compared to the regional resolution results, simulated European O3 concentrations at the global resolution are on average higher in winter and spring (10% and 6%, respectively). In contrast, simulated O3 concentrations at the global resolution are lower in summer and autumn (-1% and -4%, respectively). These differences may partly be explained by differences in nitrogen dioxide (NO2) concentrations simulated at the two resolutions.Compared to O3, we find the opposite seasonality in simulated PM2.5 differences between the two resolutions. In winter and 20 spring, simulated PM2.5 concentrations are lower at the global compared to the regional resolution (-8% and -27%, respectively) but higher in summer and autumn (29% and 8%, respectively) and are mostly related to differences in convective rainfall between the two resolutions for all seasons. These differences between the two resolutions exhibit clear spatial patterns for both pollutants that vary by season, and exert a strong influence on country to country variations in estimated AF for the two resolutions. Warm season MDA8 O3 levels are higher in most of southern Europe, but lower in areas of northern and eastern 25Europe when simulated at the global resolution compared to the regional resolution. Annual-average PM2.5 concentrations are higher across most of northern and eastern Europe but lower over parts of southwest Europe at the global compared to the regional resolution. Across Europe, differences in the AF associated with long-term exposure to population-weighted MDA8 O3 range between -0.9 % and +2.6 % (largest positive differences in southern Europe) while differences in the AF associated with long-term exposure to population-weighted annual mean PM2.5 range from -4.7% to +2.8% (largest positive differences 30Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-1074 Manuscript under review for journal Atmos. Chem. Phys. Discussion started: 28 November 2017 c Author(s) 2017. CC BY 4.0 License. 2 in eastern Europe) of the total mortality. Therefore this study, with its unique focus on Europe, demonstrates that health impact assessments calculated using modelled pollutant concentrations, are sensitive to a change in model resolution by up to ±5% of the total mortality across Europe.

No abstract