Timing matters: Intra-day shifts of economic activity and ambient ozone concentrations
中文摘要
已有研究表明，短期暴露于近地面臭氧会产生显著的负面健康外部性，因此自20世纪70年代以来，美国《清洁空气法》一直对其进行规制。臭氧并非直接排放，而是在阳光和温暖气温条件下，由多种空气污染物以一种复杂的、类似列昂惕夫的组合方式形成，导致其浓度在日间中段较高、夜间较低。尽管这一关系已广为人知，美国环境保护署的规制主要考虑臭氧前体物的排放总量，而不考虑这些排放发生的时间。利用1980年至2017年美国时区边界附近环境臭氧的逐小时数据，我们提供的证据表明，边界两侧一小时的时差会导致一天中某些时段的臭氧水平发生不可忽视的变化。随后，我们考察了一项针对臭氧前体物排放的总量控制与交易计划——氮氧化物预算计划，发现尽管该计划总体上降低了臭氧水平，但并未对这些排放的发生时点产生经济上显著的影响。最后，我们概述了一种可能的政策方案，以将臭氧前体物减排价值随时间变化的特征纳入考量。
Abstract
Ground-level ozone has been shown to have significant negative health externalities from short-term exposure, and as such has been regulated by the U.S. Clean Air Act since the 1970s. Ozone is not emitted directly; instead formation occurs due to a complex Leontief-like combination of air pollutants, under sunlight and warm temperatures, that results in high levels mid-day and low levels at night. Despite this known relationship, EPA regulations mostly consider the total emissions of ozone precursors and not when these emissions occur. Using hourly data on ambient ozone from 1980 to 2017 near the U.S. time zone borders, we provide evidence that the 1-hour time difference on either side of a border leads to a nontrivial change in ozone levels in certain hours of the day. We then examine a cap-and-trade program targeting ozone precursor emissions – the NOx Budget Program – finding that while it reduced ozone overall it did not have an economically significant effect on the timing of those emissions. We conclude by outlining a possible policy approach to account for the time-varying value of reductions in ozone precursor emissions.