Large rates of urbanisation come with externalities arising from density. These are particularly pronounced in the case of uncontrolled trash disposal. Low enforcement and fiscal capacity make local governments slow to respond to these challenges and leave space for unregulated private provision, which fails to address vast environmental and health damages. We develop a smartphone application and conduct surveys with households and informal waste collectors, to map the whole market and infrastructure for trash collection and disposal in Accra, Ghana. Leveraging experimental variation and our rich bespoke data, we estimate a structural model that captures the decisions of households, informal collectors, and disposal site operators. Counterfactual results show that halving fees at waste transfer stations correct unpriced externalities up to the social planner's choice. Welfare gains exceed policy implementation costs, but these are substantial, reaching 55% of the current budget for solid waste management. The construction of planned new infrastructure achieves lower effectiveness and requires higher costs than pricing policies. In settings with low fiscal and regulatory capacity, where direct provision, bans, or first-best pollution taxes are not feasible, limited second-best regulation can internalise environmental costs, providing a path for public service delivery through informal markets.

Do industrial policies that promote clean energy offer a "ray of hope" increasing a country's economic growth and welfare whilst simultaneously reducing carbon emissions? We study the impact of Chinese solar subsidies whose implementation by cities coincided with a dramatic fall in global solar prices. We construct new panel data on city-level solar policies, patenting and output. Using synthetic-difference-in-differences between 2004-2020, we find that production and innovation subsidies were more effective than demand-side (installation) subsidies in generating large and persistent increases in local innovation, firm numbers, output and exports. However, demand policies are most effective at reducing pollution. We build and estimate a quantitative model with endogenous innovation that takes into account business stealing and knowledge spillovers. Through the lens of this model we show that: (i) the local effects remain substantial at the aggregate level; (ii) Industrial policy explain almost two-fifths of the decline in the global cost of solar panels and over a third of the increase in Chinese innovation; (iii) Innovation subsidies are much more cost-effective than demand and production subsidies; and (iv) solar industrial policies increased Chinese welfare by 1% to 2.3%, almost as much as existing estimates of WTO Accession.

The internal structure of cities is shaped by localised production and residential externalities. Lack of sanitation gives rise to negative externalities in the form of pollution and disease transmission. Sanitation investments might therefore be essential to allow for people to tolerate density and for positive agglomeration externalities to emerge; thereby turning population density from a downside into an upside. To investigate this hypothesis, we assemble an address-level data set spanning the entire construction period of the Parisian sewage network during the 19th century. We first present event studies examining changes in firm density, residential density, land values, and disease incidences. We then leverage an urban model to estimate the impact of sewers on the strength of agglomeration and city structure. Through counterfactual analyses we examine the impact, cost-benefit, and alternative placements of sewers. Finally, we asses the extent to which sewers displaced pollution to the Parisian suburbs, affecting their long-term development.

Economic growth involves the spatial and sectoral reallocation of people and firms. How much should governments plan this reallocation, and what makes spatial planning successful? South Korea rose from poverty to become a leading industrialised economy today in a remarkably condensed timeline. The "Miracle on the Han" involved rapid urbanisation, industrial modernisation, and rural productivity growth, alongside aggressive spatial planning policies in the form of regional industrial parks, highway construction, and rural infrastructure development. We are creating a new historical database tracking all facets of South Korea's structural transformation from the mid- to late-20th century. Utilising newly digitised historical micro data on output, firms, employment, population, urbanisation, and infrastructure, we study the policies and channels through which the country achieved its remarkable transformation.

Electricity is a crucial input for modern production, yet its quality across time and space varies substantially. In this project, we ask how the endogenous allocation of electricity affects firm productivity and agglomeration. We build a unique spatial dataset combining administrative data on electricity consumption, engineering records on electricity outages, and a detailed firm panel from a national census. With this data in hand, we use a machine learning algorithm to predict the spatial allocation of outages following exogenous supply shocks. Using this as an instrument, we obtain reduced-form causal estimates of how firms respond to outages. Lastly, leveraging a dynamic spatial general equilibrium model, we compare the current equilibrium observed in the data to counterfactuals where outages are (i) reduced and, (ii) optimally adjusted to maximise welfare, taking into account the spatial misallocation in firm entry and growth across the country.

Using geolocated information on over 400,000 water points and a variety of health surveys across Sub-Saharan Africa, we document that access to functioning water and improved sanitation increases villages' resilience to high temperatures, reducing mortality and disease incidence. Leveraging machine learning techniques and rich information on the characteristics of water points, we identify that whether maintenance is private, communal, or institutional is a key determinant for a water point functional status. We design an intervention to improve the maintenance of water points when its responsibility is assigned at the community-level.