Forests accompany the cities we build. There are an estimated 5.5 billion urban trees in the United States. Globally, about 25 percent of urban land is covered by tree canopy. This study examines urban forests as a policy tool for air pollution mitigation. We study an afforestation program in...

Microgiving, a new form of digital fundraising, operates by soliciting minuscule, recurring donations from large numbers of potential donors. We evaluate a charity subscription program operated by Alibaba, China's largest retail platform, which allows sellers to pledge a tiny portion of a...