We investigate the effect of subway system openings on urban air pollution. On average, particulate concentrations are unchanged by subway openings. For cities with higher initial pollution levels, subway openings reduce particulates by 4 percent in the area surrounding a city center. The effect decays with distance to city center and persists over the longest time horizon that we can measure with our data, about four years. For highly polluted cities, we estimate that a new subway system provides an external mortality benefit of about $1 billion per year. For less polluted cities, the effect is indistinguishable from zero. Back of the envelope cost estimates suggest that reduced mortality due to lower air pollution offsets a substantial share of the construction costs of subways. (JEL I12, L92, O13, O18, Q51, Q53, R41)

中文翻译：

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地铁与城市空气污染


我们研究了地铁系统开口对城市空气污染的影响。平均而言，颗粒物浓度不会随地铁开口的变化而变化。对于初始污染水平较高的城市，地铁开口可将市中心周边区域的颗粒物减少 4%。这种影响随着距市中心的距离而减弱，并在我们可以用数据测量的最长时间范围内持续存在，大约四年。对于污染严重的城市，我们估计新的地铁系统每年可带来约 10 亿美元的外部死亡率效益。对于污染较轻的城市来说，影响几乎为零。粗略的成本估算表明，空气污染降低所带来的死亡率降低抵消了地铁建设成本的很大一部分。 (JEL I12、L92、O13、O18、Q51、Q53、R41)