@article{SchneidemesserSibiyaCaseiroetal.2021,
  author    = {Schneidemesser, Erika von and Sibiya, Bheki and Caseiro, Alexandre and Butler, Tim and Lawrence, Mark and Leitao, Joana and Lupa{\c{s}}cu, Aura and Salvador, Pedro},
  title     = {Learning from the COVID-19 lockdown in Berlin},
  series = {Atmospheric environment: X},
  volume    = {12},
  journal   = {Atmospheric environment: X},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {2590-1621},
  doi       = {10.1016/j.aeaoa.2021.100122},
  pages     = {13},
  year      = {2021},
  abstract  = {Urban air pollution is a substantial threat to human health. Traffic emissions remain a large contributor to air pollution in urban areas. The mobility restrictions put in place in response to the COVID-19 pandemic provided a large-scale real-world experiment that allows for the evaluation of changes in traffic emissions and the corresponding changes in air quality. Here we use observational data, as well as modelling, to analyse changes in nitrogen dioxide, ozone, and particulate matter resulting from the COVID-19 restrictions at the height of the lockdown period in Spring of 2020. Accounting for the influence of meteorology on air quality, we found that reduction of ca. 30-50 \% in traffic counts, dominated by changes in passenger cars, corresponded to reductions in median observed nitrogen dioxide concentrations of ca. 40 \% (traffic and urban background locations) and a ca. 22 \% increase in ozone (urban background locations) during weekdays. Lesser reductions in nitrogen dioxide concentrations were observed at urban background stations at weekends, and no change in ozone was observed. The modelled reductions in median nitrogen dioxide at urban background locations were smaller than the observed reductions and the change was not significant. The model results showed no significant change in ozone on weekdays or weekends. The lack of a simulated weekday/weekend effect is consistent with previous work suggesting that NOx emissions from traffic could be significantly underestimated in European cities by models. These results indicate the potential for improvements in air quality due to policies for reducing traffic, along with the scale of reductions that would be needed to result in meaningful changes in air quality if a transition to sustainable mobility is to be seriously considered. They also confirm once more the highly relevant role of traffic for air quality in urban areas.},
  language  = {en}
}
@article{WegerCoenenLeitaoLawrence2021,
  author    = {Weger Coenen, Lindsey and Leit{\~a}o, Joana and Lawrence, Mark},
  title     = {Expected impacts on greenhouse gas and air pollutant emissions due to a possible transition towards a hydrogen economy in German road transport},
  series = {International journal of hydrogen energy : official journal of the International Association for Hydrogen Energy},
  volume    = {46},
  journal   = {International journal of hydrogen energy : official journal of the International Association for Hydrogen Energy},
  number    = {7},
  publisher = {Elsevier},
  address   = {Oxford},
  issn      = {0360-3199},
  doi       = {10.1016/j.ijhydene.2020.11.014},
  pages     = {5875 -- 5890},
  year      = {2021},
  abstract  = {Transitioning German road transport partially to hydrogen energy is among the possibilities being discussed to help meet national climate targets. This study investigates impacts of a hypothetical, complete transition from conventionally-fueled to hydrogen-powered German transport through representative scenarios. Our results show that German emissions change between -179 and +95 MtCO(2)eq annually, depending on the scenario, with renewable-powered electrolysis leading to the greatest emissions reduction, while electrolysis using the fossilintense current electricity mix leads to the greatest increase. German energy emissions of regulated pollutants decrease significantly, indicating the potential for simultaneous air quality improvements. Vehicular hydrogen demand is 1000 PJ annually, requiring 446-525 TWh for electrolysis, hydrogen transport and storage, which could be supplied by future German renewable generation, supporting the potential for CO2-free hydrogen traffic and increased energy security. Thus hydrogen-powered transport could contribute significantly to climate and air quality goals, warranting further research and political discussion about this possibility.},
  language  = {en}
}