Search

The World Health Organization estimates that over 90% of the world's population is exposed to hazardous levels of local air pollution. Air pollution is markedly worse in low- and middle-income countries, yet air-quality monitoring is typically sparse. In 2008, the US Embassy in Beijing began tweeting hourly air-quality information from a newly installed pollution monitor, dramatically improving the information on air quality available to Beijing residents. Since then, the United States has installed over 50 monitors around the world, tweeting real-time reports on air quality in those locations. Using spatially granular measurements of local air pollution from satellite data that span the globe, we employ variation in whether and when US embassies installed monitors to evaluate the impact of air-quality information on pollution. We estimate that embassy monitors led to reductions in fine particulate concentration levels in host countries of 2 to 4 µg/m 3 . Our central estimate of the annual monetized benefit of the decrease in premature mortality due to this reduction in pollution is $127 million for the median city in 2019. Our findings point to the substantial benefits of improving the availability and salience of air-quality information in low- and middle-income countries.

Regional quarantine policies, in which a portion of a population surrounding infections is locked down, are an important tool to contain disease. However, jurisdictional governments-such as cities, counties, states, and countries-act with minimal coordination across borders. We show that a regional quarantine policy's effectiveness depends on whether 1) the network of interactions satisfies a growth balance condition, 2) infections have a short delay in detection, and 3) the government has control over and knowledge of the necessary parts of the network (no leakage of behaviors). As these conditions generally fail to be satisfied, especially when interactions cross borders, we show that substantial improvements are possible if governments are outward looking and proactive: triggering quarantines in reaction to neighbors' infection rates, in some cases even before infections are detected internally. We also show that even a few lax governments-those that wait for nontrivial internal infection rates before quarantining-impose substantial costs on the whole system. Our results illustrate the importance of understanding contagion across policy borders and offer a starting point in designing proactive policies for decentralized jurisdictions., Competing Interests: The authors declare no competing interest.

Emissions of most pollutants that result in fine particulate matter (PM 2.5 ) formation have been decreasing in the United States. However, this trend has not been uniform across all sectors or regions of the economy. We use integrated assessment models (IAMs) to compute marginal damages for PM 2.5 -related emissions for each county in the contiguous United States and match location-specific emissions with these marginal damages to compute economy-wide gross external damage (GED) due to premature mortality. We note 4 key findings: First, economy-wide, GED has decreased by more than 20% from 2008 to 2014. Second, while much of the air pollution policies have focused to date on the electricity sector, damages from farms are now larger than those from utilities. Indeed, farms have become the largest contributor to air pollution damages from PM 2.5 -related emissions. Third, 4 sectors, comprising less than 20% of the national gross domestic product (GDP), are responsible for ∼75% of GED attributable to economic activities. Fourth, uncertainty in GED estimates tends to be high for sectors with predominantly ground-level emissions because these emissions are usually estimated and not measured. These findings suggest that policymakers should target further emissions reductions from such sectors, particularly in transportation and agriculture., Competing Interests: The authors declare no conflict of interest.

Many studies find that women are more risk averse than men. Why does such a gender gap exist, and how malleable is this gender gap in risk aversion? The paper takes advantage of a rare setting in which children of the matrilineal Mosuo and the traditionally patriarchal Han attend the same schools in Yunnan, China to shed light on these questions. In particular, we exploit the fact that children would experience a shock in gender norms when they start to intermingle with children from other ethnic groups with the opposite gender norms at school. Using survey and field experiments, we elicit risk attitudes from Mosuo and Han elementary and middle school students. We find that, at the time when they first enter school, Mosuo and Han children exhibit opposite gender norms-Mosuo girls take more risks than Mosuo boys, while Han girls are more risk averse than Han boys, reflecting cultural differences. However, after Mosuo students spend more time with Han students, Mosuo girls become more and more risk averse. By age 11, Mosuo girls are also more risk averse than Mosuo boys. We also observe a shrinking gap in risk aversion for Han over time. Using random roommate assignment for boarding middle school students, we find Mosuo boys who have fewer Mosuo roommates behave more similarly to Han boys. This shows that risk preferences are shaped by culture and malleable in response to new environments., Competing Interests: The authors declare no conflict of interest., (Copyright © 2019 the Author(s). Published by PNAS.)