Atmospheric-based greenhouse gas measurements approaches can help cities achieve their climate and sustainability goals

Abstract:

A credible assessment of a city’s greenhouse gas (GHG) mitigation policies requires accurate and consistent emission data at scales that align with human activity and decision making. Presently, cities base their GHG climate mitigation policies mainly on self-reported inventories (SRIs) constructed from protocol guidelines developed by non-governmental organizations. But protocol guidelines, when practically implemented, may not yield emission information that is accurate or consistent enough to track progress toward mitigation goals. Additionally, protocols only outline the steps needed to develop a snapshot of city-wide sectoral emission information for a given year. Although useful for broad initiatives, this snapshot is often of limited use to city managers looking to develop targeted mitigation policies. To address some of these shortcomings, the research community has been developing atmospheric measurement-based approaches for estimating GHG emissions at the city scale. These approaches integrate hourly, street-level, activity-based emission information with local GHG atmospheric measurements by simulating how emissions disperse in the atmosphere. Since the emission estimates are consistent with atmospheric observations, they provide a reality check that is currently missing from protocol guidelines. In addition, because the resulting estimates are on fine time and spatial scales, they can enable targeted mitigation policies. Here, we examine the limitations of protocol guidelines for helping cities reach their mitigation objectives, demonstrate the value of quantified GHG emissions using atmospheric measurement-based approaches, and discuss future pathways for development. We focus on the City of Indianapolis to show the usefulness of quantified GHG estimates in terms of ascertaining whole-city annual trends. When compared to the city’s SRI, we show an average yearly difference of 35% over time. Ultimately, evolving city-scale emission estimation methods will require finding complementary aspects of both the protocol and measurement-based approaches to form an internationally recognized, multi-faceted reference framework. Such a structure will help avoid duplication, ensure uniformity, and provide accuracy of city-scale emissions needed to tackle climate change.