Mid-21st century air quality at the urban scale under the influence of changed climate and emissions – case studies for Paris and Stockholm

Abstract

Abstract. Ozone, PM 10 and PM 2.5 concentrations over Paris, France and Stockholm, Sweden were modelled at 4 and 1 km horizontal resolutions respectively for the present and 2050 periods employing decade-long simulations. We account for large-scale global climate change (RCP-4.5) and fine-resolution bottom-up emission projections developed by local experts and quantify their impact on future pollutant concentrations. Moreover, we identify biases related to the implementation of regional-scale emission projections by comparing modelled pollutant concentrations between the fine-and coarse-scale simulations over the study areas. We show that over urban areas with major regional contribution (e.g. the city of Stockholm) the bias related to coarse-scale projections may be significant and lead to policy misclassification. Our results stress the need to better understand the mechanism of bias propagation across the modelling scales in order to design more successful local-scale strategies. We find that the impact of climate change is spatially homogeneous in both regions, implying strong regional influence. The climate benefit for ozone (daily mean and maximum) is up to −5 % for Paris and −2 % for Stockholm city. The climate benefit on PM 2.5 and PM 10 in Paris is between −5 and −10 %, while for Stockholm we estimate mixed trends of up to 3 % depending on season and size class. In Stockholm, emission mitigation leads to concentration reductions up to 15 % for daily mean and maximum ozone and 20 % for PM. Through a sensitivity analysis we show that this response is entirely due to changes in emissions at the regional scale. On the contrary, over the city of Paris (VOC-limited photochemical regime), local mitigation of NO x emissions increases future ozone concentrations due to ozone titration inhibition. This competing trend between the respective roles of emission and climate change, results in an increase in 2050 daily mean ozone by 2.5 % in Paris. Climate and not emission change appears to be the most influential factor for maximum ozone concentration over the city of Paris, which may be particularly interesting from a health impact perspective.

Reanalysis of and attribution to near-surface ozone concentrations in Sweden during 1990–2013

“…In the following sections we briefly describe the utilized input data. Further details of MATCH in the present model version and its ability to simulate near-surface O 3 can be found in separate publications, for example Markakis et al (2016), Lacressoniere et al (2016) and Watson et al (2015Watson et al ( , 2016.…”

“…5 km height, which is the model's standard configuration for pan-European simulations. The selected setup has been demonstrated (e.g., Andersson et al, 2007;Langner et al, 2012a;Markakis et al, 2016) to be adequate for describing near-surface O 3 across Europe although trends in stratospheric chemistry or physically driven changes in stratospheric-tropospheric exchanges will likely not be captured.…”

Ozone and heat-related mortality in Europe in 2050 significantly affected by changes in climate, population and greenhouse gas emission

“…This means that ozone exposure was likely overestimated close to where high emissions occur (e.g. Markakis et al 2016), but underestimated in suburban areas in the outskirts of city centres where local emissions could increase near-surface ozone. Measures to reduce NO emissions locally may have the counter-benefit of increasing ozone exposure.…”

“…The methods for calculating European-wide (EU-27, Norway, Switzerland) near-surface temperature and ozone concentrations are described elsewhere (Lacressonnière et al 2016, Markakis et al 2016, Watson et al 2016. In summary, both climate and air pollution were modelled at a horizontal resolution of 0.44°× 0.44°(ca 50 km×50 km) covering Europe (the full domain is the EURO-CORDEX domain, which is slightly larger than that which is shown in this analysis).…”

“…The CLE describes enforcement of all current legislative measures until 2030, but no additional measures, and has smaller decreases in precursor emissions compared to the MTF. Projections of future near-surface ozone concentrations, based on such future emission scenarios, result in a strong decrease in future ozone concentrations in Europe (Markakis et al 2016, Watson et al 2016.…”