@phdthesis{Schmitz2023,
  author    = {Schmitz, Se{\´a}n},
  title     = {Using low-cost sensors to gather high resolution measurements of air quality in urban environments and inform mobility policy},
  doi       = {10.25932/publishup-60105},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-601053},
  school      = {Universit{\"a}t Potsdam},
  pages     = {180},
  year      = {2023},
  abstract  = {Air pollution has been a persistent global problem in the past several hundred years. While some industrialized nations have shown improvements in their air quality through stricter regulation, others have experienced declines as they rapidly industrialize. The WHO's 2021 update of their recommended air pollution limit values reflects the substantial impacts on human health of pollutants such as NO2 and O3, as recent epidemiological evidence suggests substantial long-term health impacts of air pollution even at low concentrations. Alongside developments in our understanding of air pollution's health impacts, the new technology of low-cost sensors (LCS) has been taken up by both academia and industry as a new method for measuring air pollution. Due primarily to their lower cost and smaller size, they can be used in a variety of different applications, including in the development of higher resolution measurement networks, in source identification, and in measurements of air pollution exposure. While significant efforts have been made to accurately calibrate LCS with reference instrumentation and various statistical models, accuracy and precision remain limited by variable sensor sensitivity. Furthermore, standard procedures for calibration still do not exist and most proprietary calibration algorithms are black-box, inaccessible to the public. This work seeks to expand the knowledge base on LCS in several different ways: 1) by developing an open-source calibration methodology; 2) by deploying LCS at high spatial resolution in urban environments to test their capability in measuring microscale changes in urban air pollution; 3) by connecting LCS deployments with the implementation of local mobility policies to provide policy advice on resultant changes in air quality. In a first step, it was found that LCS can be consistently calibrated with good performance against reference instrumentation using seven general steps: 1) assessing raw data distribution, 2) cleaning data, 3) flagging data, 4) model selection and tuning, 5) model validation, 6) exporting final predictions, and 7) calculating associated uncertainty. By emphasizing the need for consistent reporting of details at each step, most crucially on model selection, validation, and performance, this work pushed forward with the effort towards standardization of calibration methodologies. In addition, with the open-source publication of code and data for the seven-step methodology, advances were made towards reforming the largely black-box nature of LCS calibrations. With a transparent and reliable calibration methodology established, LCS were then deployed in various street canyons between 2017 and 2020. Using two types of LCS, metal oxide (MOS) and electrochemical (EC), their performance in capturing expected patterns of urban NO2 and O3 pollution was evaluated. Results showed that calibrated concentrations from MOS and EC sensors matched general diurnal patterns in NO2 and O3 pollution measured using reference instruments. While MOS proved to be unreliable for discerning differences among measured locations within the urban environment, the concentrations measured with calibrated EC sensors matched expectations from modelling studies on NO2 and O3 pollution distribution in street canyons. As such, it was concluded that LCS are appropriate for measuring urban air quality, including for assisting urban-scale air pollution model development, and can reveal new insights into air pollution in urban environments. To achieve the last goal of this work, two measurement campaigns were conducted in connection with the implementation of three mobility policies in Berlin. The first involved the construction of a pop-up bike lane on Kottbusser Damm in response to the COVID-19 pandemic, the second surrounded the temporary implementation of a community space on B{\"o}ckhstrasse, and the last was focused on the closure of a portion of Friedrichstrasse to all motorized traffic. In all cases, measurements of NO2 were collected before and after the measure was implemented to assess changes in air quality resultant from these policies. Results from the Kottbusser Damm experiment showed that the bike-lane reduced NO2 concentrations that cyclists were exposed to by 22 ± 19\%. On Friedrichstrasse, the street closure reduced NO2 concentrations to the level of the urban background without worsening the air quality on side streets. These valuable results were communicated swiftly to partners in the city administration responsible for evaluating the policies' success and future, highlighting the ability of LCS to provide policy-relevant results. As a new technology, much is still to be learned about LCS and their value to academic research in the atmospheric sciences. Nevertheless, this work has advanced the state of the art in several ways. First, it contributed a novel open-source calibration methodology that can be used by a LCS end-users for various air pollutants. Second, it strengthened the evidence base on the reliability of LCS for measuring urban air quality, finding through novel deployments in street canyons that LCS can be used at high spatial resolution to understand microscale air pollution dynamics. Last, it is the first of its kind to connect LCS measurements directly with mobility policies to understand their influences on local air quality, resulting in policy-relevant findings valuable for decisionmakers. It serves as an example of the potential for LCS to expand our understanding of air pollution at various scales, as well as their ability to serve as valuable tools in transdisciplinary research.},
  language  = {en}
}
@techreport{BorckSchrauth2022,
  type      = {Working Paper},
  author    = {Borck, Rainald and Schrauth, Philipp},
  title     = {Urban pollution},
  series = {CEPA Discussion Papers},
  journal   = {CEPA Discussion Papers},
  number    = {60},
  issn      = {2628-653X},
  doi       = {10.25932/publishup-57204},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-572049},
  pages     = {48},
  year      = {2022},
  abstract  = {We use worldwide satellite data to analyse how population size and density affect urban pollution. We find that density significantly increases pollution exposure. Looking only at urban areas, we find that population size affects exposure more than density. Moreover, the effect is driven mostly by population commuting to core cities rather than the core city population itself. We analyse heterogeneity by geography and income levels. By and large, the influence of population on pollution is greatest in Asia and middle-income countries. A counterfactual simulation shows that PM2.5 exposure would fall by up to 36\% and NO2 exposure up to 53\% if within countries population size were equalized across all cities.},
  language  = {en}
}
@techreport{GohlSchrauth2022,
  type      = {Working Paper},
  author    = {Gohl, Niklas and Schrauth, Philipp},
  title     = {Ticket to Paradise?},
  series = {CEPA Discussion Papers},
  journal   = {CEPA Discussion Papers},
  number    = {50},
  issn      = {2628-653X},
  doi       = {10.25932/publishup-55846},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-558466},
  pages     = {20},
  year      = {2022},
  abstract  = {This paper provides novel evidence on the impact of public transport subsidies on air pollution. We obtain causal estimates by leveraging a unique policy intervention in Germany that temporarily reduced nationwide prices for regional public transport to a monthly flat rate price of 9 Euros. Us-ing DiD estimation strategies on air pollutant data, we show that this intervention causally reduced a benchmark air pollution index by more than six percent. Our results illustrate that public transport subsidies - especially in the context of spatially constrained cities - offer a viable alterna-tive for policymakers and city planers to improve air quality, which has been shown to crucially affect health outcomes.},
  language  = {en}
}
@techreport{BorckSchrauth2019,
  type      = {Working Paper},
  author    = {Borck, Rainald and Schrauth, Philipp},
  title     = {Population density and urban air quality},
  series = {CEPA Discussion Papers},
  journal   = {CEPA Discussion Papers},
  number    = {8},
  issn      = {2628-653X},
  doi       = {10.25932/publishup-42771},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-427719},
  pages     = {53},
  year      = {2019},
  abstract  = {We use panel data from Germany to analyze the effect of population density on urban air pollution (nitrogen oxides, particulate matter and ozone). 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. Our preferred estimates imply that a one-standard deviation increase in population density increases air pollution by 3-12\%.},
  language  = {en}
}
@phdthesis{GohlGreenaway2023,
  author    = {Gohl-Greenaway, Niklas},
  title     = {Essays in public economics},
  doi       = {10.25932/publishup-60902},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-609026},
  school      = {Universit{\"a}t Potsdam},
  pages     = {10, 291},
  year      = {2023},
  abstract  = {This cumulative dissertation uses economic theory and micro-econometric tools and evaluation methods to analyse public policies and their impact on welfare and individual behaviour. In particular, it focuses on policies in two distinct areas that represent fundamental societal challenges in the 21st century: the ageing of society and life in densely-populated urban agglomerations. Together, these areas shape important financial decisions in a person's life, impact welfare, and are driving forces behind many of the challenges in today's societies. The five self-contained research chapters of this thesis analyse the forward looking effects of pension reforms, affordable housing policies as well as a public transport subsidy and its effect on air pollution.},
  language  = {en}
}