Using rapid expansion of the Beijing subway from 2000 to 2018, we analyze its impact on collaborative matches in innovations. We find that an hour reduction in travel time between a pair of locations in Beijing brought 14.85% to 37.69% increase in collaborated patents. Far-apart location pairs were more affected, and the local average causal response is approximately 34.92% to 82.29%. The effect is mainly driven by increased matches among highly productive innovators. The entry of new innovators, relocation of existing innovators, and collaborations among low-productive innovators also contribute to the increase in collaborative matches, especially in the long run.

This paper examines the effects of work experience acquired while youth were in high school (and college) on young men's wage rates. Previous studies have found sizeable and persistent rates of return to working while enrolled in school, especially high school, on subsequent wage growth. We evaluate the extent to which these estimates represent causal effects by assessing the robustness of prior findings to controls for unobserved heterogeneity and sample selectivity. We explore more-general econometric methods for dealing with the dynamic of selection and apply them to data on young men from the 1979 National Longitudinal Survey of Youth (NLSY79). We find that the estimated returns to working while in high school or college are dramatically diminished in magnitude and are not statistically significant when one applies dynamic selection methods.

Urban forests are ubiquitous, yet their impacts and values remain largely unknown. We study a massive urban afforestation policy in Beijing that planted 1/3 of a million acres of greenery in less than a decade. We conduct a remote-sensing audit of the program, finding that it contributes to a substantial greening up of the city. This causes significant downwind air quality improvement, reducing average PM2.5 concentration at city population hubs by 4.2%. Rapid vegetation growth unexpectedly led to a 7.4% increase in pollen exposure. Analysis of medical claims data shows that increased aeroallergens triggered emergency room visits, mirroring pollution effects though much less severe. Monetized net health benefits of the program amount to 1.5% of the city’s GDP. Urban forests are only partially capitalized in housing values, with buyers mainly appreciating proximity to green spaces but not the air quality improvements they bring.