文 | YE Qianlin
本文继续应景“穹顶之下”所引发的环境讨论。这个关于北京车辆限行对空气污染和经济活动的研究从09年就开始了,但多年后才发出来,多么不容易呀。个人认为,这篇文章从微观层面验证了短期内减轻污染和增加经济活动(labor supply)之间的确存在trade-off,但cost-benefit ananlysis显示收益大于成本,主要是因为reduced pollution提高了人们的健康水平。但治理污染会损害经济增长吗?我认为理论上这需要建立一个structual model,实证上需要长期的跨国宏观数据。柴静在“穹顶之下”中提到,英国大烟雾事件后,治理污染的同时并没有出现经济下行,GDP反而番了四倍,就业人数也增长了。但经济学家如果可以用structual model给出counterfactual results(不治理环境会怎么样),对我而言会更有说服力。
This paper identified the causal effects of Beijing’s Odd-Even and One-Day-Per-Week driving restrictions on reduced pollution (particular matters) and reduced economic activities (labor supply). To see the effect on aggregate pollution, they used an RD design to exploit both time-series and spatial variation. Their point estimates indicated that the every-other-day restrictions reduced particulate matter by 18% and one-day-a-week restrictions by 21%.
To measure the effect on labor supply, they divided workers into two categories: self-employed and hourly workers. The proxy for working time is TV viewership, which biases the effect because the reduced auto congestion and pollution may make outdoor activities more attractive relative to indoor TV viewership. Therefore, they considered viewership during restricted hours and outside hours separately. For self-employed workers, viewership increases by 8.9 to 16.9% during the restricted hours of the one-day-a-week policy while viewership changes little outside the restricted hours ruling out the possibility that longer daily working hours offset fewer working days. Since hourly worker cannot adjust their schedule flexibly, their viewership during the restricted hours should be unaffected. But there is a decrease in their viewership due to fewer at-home sick days resulting from reduced pollution. Changes outside restricted hours are minor, too.
The high compliance of workers suggests the driving restrictions’ success. But lessons from other countries show that the effects may be compensated by buying more cars to throw off the shackles. At the end of the paper, it's emphasized that the effects are short-run. On the long run, as income in China increases, the compensating response is likely.
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