@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{MarUngerWalderdorffetal.2022,
  author    = {Mar, Kathleen A. and Unger, Charlotte and Walderdorff, Ludmila and Butler, Tim},
  title     = {Beyond CO2 equivalence},
  series = {Environmental science \& policy},
  volume    = {134},
  journal   = {Environmental science \& policy},
  publisher = {Elsevier},
  address   = {Oxford},
  issn      = {1462-9011},
  doi       = {10.1016/j.envsci.2022.03.027},
  pages     = {127 -- 136},
  year      = {2022},
  abstract  = {In this article we review the physical and chemical properties of methane (CH4) relevant to impacts on climate, ecosystems, and air pollution, and examine the extent to which this is reflected in climate and air pollution governance. Although CH4 is governed under the UNFCCC climate regime, its treatment there is limited to the ways in which it acts as a "CO2 equivalent" climate forcer on a 100-year time frame. The UNFCCC framework neglects the impacts that CH4 has on near-term climate, as well its impacts on human health and ecosystems, which are primarily mediated by methane's role as a precursor to tropospheric ozone. Frameworks for air quality governance generally address tropospheric ozone as a pollutant, but do not regulate CH4 itself. Methane's climate and air quality impacts, together with its alarming rise in atmospheric concentrations in recent years, make it clear that mitigation of CH4 emissions needs to be accelerated globally. We examine challenges and opportunities for further progress on CH4 mitigation within the international governance landscapes for climate change and air pollution.},
  language  = {en}
}
@article{BorckSchrauth2020,
  author    = {Borck, Rainald and Schrauth, Philipp},
  title     = {Population density and urban air quality},
  series = {Regional science and urban economics},
  volume    = {86},
  journal   = {Regional science and urban economics},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {0166-0462},
  doi       = {10.1016/j.regsciurbeco.2020.103596},
  pages     = {24},
  year      = {2020},
  abstract  = {We use panel data from Germany to analyze the effect of population density on urban air pollution (nitrogen oxides, particulate matter, ozone, and an aggregate index for bad air quality [AQI]). To address unobserved heterogeneity and omitted variables, we present long difference/fixed effects estimates and instrumental variables estimates, using historical population and soil quality as instruments. Using our preferred estimates, we find that the concentration increases with density for NO2 with an elasticity of 0.25 and particulate matter with elasticity of 0.08. The O-3 concentration decreases with density with an elasticity of -0.14. The AQI increases with density, with an elasticity of 0.11-0.13. We also present a variety of robustness tests. Overall, the paper shows that higher population density worsens local air quality.},
  language  = {en}
}