Developing megacities face severe congestion externalities but lack the fiscal and enforcement capacity for textbook regulation. In its absence, unregulated private provision emerges across services like waste, sanitation, water, and transport. We ask whether limited, feasible regulation can leverage these informal markets to deliver public services at scale, focusing on trash collection in Accra, Ghana. Using novel data, we document an imperfect but functioning market: households pay informal tricycle collectors for door-to-door service, yet prices remain too high for universal access, and final disposal occurs largely at illegal dumpsites. We identify a single feasible lever — subsidies for formal, environmentally controlled disposal — and evaluate it using a new structural model of urban waste collection and disposal. To estimate the model, we combine survey experiments eliciting household demand, a custom app recording transactions and tricycle routes, and a field experiment randomising dumping fees. A modest subsidy captures roughly 80% of the first-best welfare gain, substantially reducing environmental damages and generating larger gains at lower cost than planned infrastructure expansion. Limited price-based regulation can align informal private initiative with social objectives even where state capacity is weak.

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.

Urban density promises agglomeration benefits but also exacerbates pollution and disease transmission. Sanitation infrastructure may therefore be essential for cities to sustain dense concentrations of economic activity. To study how sanitation investments shape urban development, we compile a novel address-level dataset covering the construction of the Parisian sewer network in the nineteenth century. Exploiting within-neighbourhood variation in the timing of sewer connections in an event-study design, we find that connecting a parcel to the sewer network increases both population and firm counts. Sewer connections in nearby locations generate additional increases, with larger spillovers in more densely populated areas. We incorporate these findings into a quantitative urban model and estimate that sewer access increases residential amenity values by 2.5% and firm productivity by 5% in connected locations. The analysis further reveals that, in unsewered areas, the marginal effect of additional people on others’ utility turns negative as neighbourhoods densify and pollution costs intensify. Sewers eliminate this downturn. Counterfactuals indicate that sewerage investments account for 30% of Paris’ population growth in the second half of the nineteenth century. One-quarter of this effect operates through reductions in negative sanitation externalities, while the remainder reflects the private benefits of sewer access. These findings highlight how addressing waste pollution can lower the costs of proximity and sustain urban growth.